MAX6581ATG9A+ - Maxim Integrated

19-5260; Rev 4; 2/19

General Description

The MAX6581 precision multichannel temperature

sensor monitors its own temperature and the temperatures

of up to seven external diode-connected transistors. All

temperature channels have programmable alert and over-

temperature thresholds. When the measured temperature

of a channel crosses the respective threshold, a status bit

is set in one of the status registers. Two open-drain alarm

outputs (ALERT and OVERT) assert corresponding to

these bits in the status register(s).

Resistance cancellation is available for all channels and

compensates for high series resistance in circuit-board

traces and thermal diodes.

The 2-wire serial interface accepts SMBus protocols

(write byte, read byte, send byte, and receive byte) for

reading the temperature data and programming the alarm

thresholds.

The MAX6581 is specified for an operating temperature

range of -40°C to +125°C and is available in a 24-pin,

4mm x 4mm thin QFN package with an exposed pad.

Features

●Eight Channels to Measure Seven Remote and One

Local Temperature

●11-Bit, 0.125°C Resolution

●High Accuracy of ±1°C (max) from +60°C to +100°C

(Remote Channels)

●-64°C to +150°C Remote Temperature Range

●Programmable Undertemperature/Overtemperature

Alerts

●SMBus/I2C-Compatible Interface

●Two Open-Drain Alarm Outputs (ALERT and OVERT)

●Resistance Cancellation on All Remote Channels

Applications

●Desktop Computers

●Notebook Computers

●Workstations

●Servers

●Data Communications

Typical Application Circuit appears at end of data sheet.

Note: All devices are specified over the -40°C to +125°C operating temperature range.

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

**Future product—contact factory for availability.

PART SLAVE ADDRESS PIN-PACKAGE OPERATING

TEMPERATURE RANGE

MEASURED

TEMPERATURE RANGE

MAX6581TG9A+ 0X9A 24 TQFN-EP* -40°C to +125°C -64°C to +150°C

MAX6581TG9C+** 0X9C 24 TQFN-EP* -40°C to +125°C -64°C to +150°C

MAX6581TG9E+** 0X9E 24 TQFN-EP* -40°C to +125°C -64°C to +150°C

MAX6581TG98+** 0X98 24 TQFN-EP* -40°C to +125°C -64°C to +150°C

Click here for production status of specic part numbers.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

Ordering Information/Selector Guide

EVALUATION KIT AVAILABLE

(Note 1)

(All voltages referenced to GND.)

VCC, SMBCLK, SMBDATA, ALERT,

OVERT, STBY to GND ........................................ -0.3V to +4V

DXP_ to GND ........................................... -0.3V to (VCC + 0.3V)

DXN_ to GND ........................................... -0.3V to (VCC + 0.3V)

SMBDATA, ALERT, OVERT Current.................. -1mA to +50mA

DXN_ Current ..................................................................... ±1mA

Continuous Power Dissipation (TA = +70°C)

TQFN (derate 27.8mW/°C above +70°C)..................2222mW

ESD Protection (All Pins, Human Body Model) ..................±2kV

Operating Temperature Range ......................... -40°C to +125°C

Junction Temperature ...................................................... +150°C

Storage Temperature Range ........................... -65°C to +150°C

Lead Temperature (soldering, 10s) ................................+300°C

Soldering Temperature (reflow) ....................................... +260°C

TQFN

Junction-to-Ambient Thermal Resistance (θJA) ......36.0°C/W

Junction-to-Case Thermal Resistance (θJC) ..............3.0°C/W

(VCC = +3.0V to +3.6V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage VCC 3.0 3.6 V

Standby Supply Current ISS SMBus static 4 15 µA

Operating Current ICC1 During conversion, RC o󰀨 500 600 µA

ICC2 During conversion, RC on 550 650

Temperature Resolution 11 Bits

0.125 °C

3-Sigma Temperature Accuracy

(Remote Channels 1–7) VCC = 3.3V

TA = +30°C to +85°C,

TRJ = +60°C to +100°C -0.85 +0.85

°CTA, TRJ = -40°C to +125°C -1.2 +1.2

TA = +30°C to +85°C,

TRJ = +100°C to +150°C -2.5 +2.5

3-Sigma Temperature Accuracy

(Local) VCC = 3.3V

TA = +30°C to +85°C -1 +1

°CTA = -40°C to +125°C -2 +2

TA = 0°C to +150°C -3 +3

6-Sigma Temperature Accuracy

(Remote Channels 1–7) VCC = 3.3V

TA = +30°C to +85°C,

TRJ = +60°C to +100°C -1 +1

°CTA, TRJ = -40°C to +125°C -2 +2

TA = +30°C to +85°C,

TRJ = +100°C to +125°C -2.75 +2.75

6-Sigma Temperature Accuracy

(Local) VCC = 3.3V

TA = +30°C to +85°C -1.5 +1.5

°CTA = -40°C to +125°C -2.5 +2.5

TA = 0°C to +150°C -3.5 +3.5

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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Absolute Maximum Ratings

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these

or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect

device reliability.

Electrical Characteristics

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer

board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.

Package Thermal Characteristics

(VCC = +3.0V to +3.6V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Sensitivity of Temperature

Accuracy ±0.2 °C/V

Conversion Time per Channel tCONV

Resistance cancellation mode o󰀨 95 125 156

Resistance cancellation mode on or beta

compensation on 190 250 312

Remote-Diode Source Current IRJ

High level Resistance cancellation

mode o󰀨

80 100 120

µA

Low level 8 10 12

High level Resistance cancellation

mode on or beta

compensation on

160 200 240

Low level 16 20 24

DXP_ and DXN_ Leakage Current Standby mode 100 nA

Undervoltage Lockout Threshold UVLO Falling edge of VCC disables ADC 2.25 2.80 2.95 V

Undervoltage Lockout Hysteresis 90 mV

Power-On-Reset (POR)

Threshold VCC falling edge 1.3 2.0 2.2 V

POR Threshold Hysteresis 90 mV

ALERT and OVERT

Output Low Voltage VOL

ISINK = 1mA 0.01 V

ISINK = 6mA 0.3

Input Leakage Current ILEAK -1 +1 µA

SMBus INTERFACE, STBY

Logic Input Low Voltage VIL VCC = 3.6V 0.8 V

Logic Input High Voltage VIH VCC = 3.0V 2.2 V

Input Leakage Current -1 +1 µA

Output Low Voltage VOL ISINK = 6mA 0.1 V

Input Capacitance CIN 5 pF

SMBus-COMPATIBLE TIMING (Figures 3 and 4) (Note 3)

Serial-Clock Frequency fSMBCLK (Note 4) 400 kHz

Bus Free Time Between STOP

and START Condition tBUF fSMBCLK = 400kHz 1.6 µs

START Condition Setup Time fSMBCLK = 400kHz 0.6 µs

Repeated START Condition

Setup Time tSU:STA 90% of SMBCLK to 90% of SMBDATA,

fSMBCLK = 400kHz 50 ns

START Condition Hold Time tHD:STA

10% of SMBDATA to 90% of SMBCLK,

fSMBCLK = 400kHz 0.6 µs

STOP Condition Setup Time tSU:STO

90% of SMBCLK to 90% of SMBDATA,

fSMBCLK = 400kHz 0.6 µs

Clock Low Period tLOW 10% to 10%, fSMBCLK = 400kHz 1 µs

Clock High Period tHIGH 90% to 90% 0.6 µs

Data-In Hold Time tHD:DAT 0 0.9 µs

Data-In Setup Time tSU:DAT (Note 5) 100 ns

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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Electrical Characteristics (continued)

(VCC = +3.0V to +3.6V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25°C.) (Note 2)

Note 2: All parameters are tested at TA = +85°C. Specifications over temperature are guaranteed by design.

Note 3: Timing specifications are guaranteed by design.

Note 4: The serial interface resets when SMBCLK is low for more than tTIMEOUT.

Note 5: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling

edge.

(VCC = +3.3V, VSTBY = VCC, TA = +25°C, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Receive SMBCLK/SMBDATA

Rise Time tR300 ns

Receive SMBCLK/SMBDATA Fall

Time tF300 ns

Data-Out Hold Time tDH 50 ns

Pulse Width of Spike Suppressed tSP 0 50 ns

SMBus Timeout tTIMEOUT SMBDATA low period for interface reset 25 37 45 ms

AVERAGE OPERATING SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6581 toc02

SUPPLY VOLTAGE (V)

AVERAGE OPERATING SUPPLY CURRENT (µA)

3.53.43.1 3.2 3.3

365

370

375

380

385

390

395

400

360

3.0 3.6

RESISTANCE

CANCELLATION OFF

REMOTE-DIODE TEMPERATURE ERROR

vs. REMODE-DIODE TEMPERATURE

MAX6581 toc03

REMOTE-DIODE TEMPERATURE (°C)

REMOTE-DIODE TEMPERATURE ERROR (°C)

1109050 703010

-3

-2

-1

-4

-5

-6

-7

-8

-9

-10 -10 130

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX6581 toc01

SUPPLY VOLTAGE (V)

STANDBY SUPPLY CURRENT (µA)

3.53.43.33.23.1

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

3.0 3.6

HARDWARE OR SOFTWARE

STANDBY SUPPLY CURRENT

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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Electrical Characteristics (continued)

Typical Operating Characteristics

(VCC = +3.3V, VSTBY = VCC, TA = +25°C, unless otherwise noted.)

LOCAL TEMPERATURE ERROR

vs. DIE TEMPERATURE

MAX6581 toc04

DIE TEMPERATURE (°C)

LOCAL TEMPERATURE ERROR (°C)

908060 7010 20 30 40 500

-4

-3

-2

-1

-5

-10 100

REMOTE-DIODE TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6581 toc05

POWER-SUPPLY NOISE FREQUENCY (MHz)

REMOTE-DIODE TEMPERATURE ERROR (°C)

10.10.01

-4

-3

-2

-1

-5

0.001 10

100mVP-P

TRJ = +85°C

LOCAL TEMPERATURE ERROR

vs. POWER-SUPPLY NOISE FREQUENCY

MAX6581 toc06

POWER-SUPPLY NOISE FREQUENCY (MHz)

LOCAL TEMPERATURE ERROR (°C)

10.10.01

-4

-3

-2

-1

-5

0.001 10

100mVP-P

REMOTE-DIODE TEMPERATURE ERROR

vs. CAPACITANCE

MAX6581 toc07

CAPACITANCE (nF)

REMOTE-DIODE TEMPERATURE ERROR (°C)

-4

-3

-2

-1

-5

1 100

100mVP-P

TRJ = +85°C

REMOTE-DIODE TEMPERATURE ERROR

vs. RESISTANCE

MAX6581 toc08

RESISTANCE (Ω)

REMOTE-DIODE TEMPERATURE ERROR (°C)

908060 7020 30 40 5010

-5

0 100

TRJ = +85°C

RESISTANCE

CANCELLATION OFF

RESISTANCE

CANCELLATION ON

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

Maxim Integrated

│

www.maximintegrated.com

Typical Operating Characteristics (continued)

PIN NAME FUNCTION

1 DXP2

Combined Current Source and ADC Positive Input for Channel 2 Remote Diode. Connect DXP2 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP2 unconnected or

connect to DXN2 if a remote diode is not used. Connect a 100pF capacitor between DXP2 and DXN2

for noise ltering.

2 DXN2

Cathode Input for Channel 2 Remote Diode. Connect the cathode of the channel 2 remote-diode-

connected transistor to DXN2. If the channel 2 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN2. Leave DXN2 unconnected or connect to DXP2 if a remote

diode is not used. Connect a 100pF capacitor between DXP2 and DXN2 for noise ltering.

3 DXP3

Combined Current Source and ADC Positive Input for Channel 3 Remote Diode. Connect DXP3 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP3 unconnected or

connect to DXN3 if a remote diode is not used. Connect a 100pF capacitor between DXP3 and DXN3

for noise ltering.

4 DXN3

Cathode Input for Channel 3 Remote Diode. Connect the cathode of the channel 3 remote-diode-

connected transistor to DXN3. If the channel 3 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN3. Leave DXN3 unconnected or connect to DXP3 if a remote

diode is not used. Connect a 100pF capacitor between DXP3 and DXN3 for noise ltering.

5 DXP4

Combined Current Source and ADC Positive Input for Channel 4 Remote Diode. Connect DXP4 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP4 unconnected or

connect to DXN4 if a remote diode is not used. Connect a 100pF capacitor between DXP4 and DXN4

for noise ltering.

6, 22 N.C. No Connection. Connect to other N.C. or leave unconnected.

DXN2

DXN3

DXP4

N.C.

DXP2

VCC

I.C.

STBY

ALERT

DXP7

1 2

N.C.

4 5 6

1718 16 14 13

DXP1

DXN1

DXN6

DXN5

DXP5

DXN4

MAX6581

DXP3 OVERT

GND

20 11 DXP6

SMBCLK

19 12 DXN7

SMBDATA

TOP VIEW

*EP = EXPOSED PAD, CONNECT TO GND

*EP

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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Pin Description

Pin Conguration

PIN NAME FUNCTION

7 DXN4

Cathode Input for Channel 4 Remote Diode. Connect the cathode of the channel 4 remote-diode-

connected transistor to DXN4. If the channel 4 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN4. Leave DXN4 unconnected or connect to DXP4 if a remote

diode is not used. Connect a 100pF capacitor between DXP4 and DXN4 for noise ltering.

8 DXP5

Combined Current Source and ADC Positive Input for Channel 5 Remote Diode. Connect DXP5 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP5 unconnected or

connect to DXN5 if a remote diode is not used. Connect a 100pF capacitor between DXP5 and DXN5

for noise ltering.

9 DXN5

Cathode Input for Channel 5 Remote Diode. Connect the cathode of the channel 5 remote-diode-

connected transistor to DXN5. If the channel 5 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN5. Leave DXN5 unconnected or connect to DXP5 if a remote

diode is not used. Connect a 100pF capacitor between DXP5 and DXN5 for noise ltering.

10 DXN6

Cathode Input for Channel 6 Remote Diode. Connect the cathode of the channel 6 remote-diode-

connected transistor to DXN6. If the channel 6 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN6. Leave DXN6 unconnected or connect to DXP6 if a remote

diode is not used. Connect a 100pF capacitor between DXP6 and DXN6 for noise ltering.

11 DXP6

Combined Current Source and ADC Positive Input for Channel 6 Remote Diode. Connect DXP6 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP6 unconnected or

connect to DXN6 if a remote diode is not used. Connect a 100pF capacitor between DXP6 and DXN6

for noise ltering.

12 DXN7

Cathode Input for Channel 7 Remote Diode. Connect the cathode of the channel 7 remote-diode-

connected transistor to DXN7. If the channel 7 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN7. Leave DXN7 unconnected or connect to DXP7 if a remote

diode is not used. Connect a 100pF capacitor between DXP7 and DXN7 for noise ltering.

13 DXP7

Combined Current Source and ADC Positive Input for Channel 7 Remote Diode. Connect DXP7 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP7 unconnected or

connect to DXN7 if a remote diode is not used. Place a 100pF capacitor between DXP7 and DXN7 for

noise ltering.

14 STBY Active-Low Standby Input. Drive STBY logic-low to place the MAX6581 in standby mode, or logic-high

for normal mode. Temperature and threshold data are retained in standby mode.

15 I.C. Internally Connected. I.C. is internally connected to VCC. Connect I.C. to VCC or leave unconnected.

16 OVERT Overtemperature Active-Low, Open-Drain Output. OVERT asserts low when the temperature of any

remote channel exceeds the programmed threshold limit.

17 VCC Supply Voltage Input. Bypass to GND with a 0.1µF capacitor.

18 ALERT SMBus Alert (Interrupt), Active-Low, Open-Drain Output. ALERT asserts low when the temperature of

any channel crosses a programmed ALERT high or low threshold.

19 SMBDATA SMBus Serial-Data Input/Output. Connect SMBDATA to a pullup resistor.

20 SMBCLK SMBus Serial-Clock Input. Connect SMBCLK to a pullup resistor.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Pin Description (continued)

Detailed Description

The MAX6581 is a precision multichannel tempera-

ture monitor that features one local and seven remote

temperature-sensing channels with a programmable alert

threshold for each temperature channel and a program-

mable overtemperature threshold for channels 1–7 (see

Figure 1). Communication with the MAX6581 is achieved

through the SMBus serial interface and a dedicated alert

pin (ALERT). The alarm outputs, (OVERT and ALERT)

assert if the software-programmed temperature thresh-

olds are exceeded. ALERT also asserts if the measured

temperature falls below the ALERT low limits. ALERT

typically serves as an interrupt, while OVERT can be

connected to a fan, system shutdown, or other thermal-

management circuitry.

ADC Conversion Sequence

The MAX6581 starts the conversion sequence by

measuring the temperature on channel 1, followed by 2,

local channel, 3–7. The conversion result for each active

channel is stored in the corresponding temperature data

does not have a diode.

Low-Power Standby Mode

Enter software-standby mode by setting the STOP bit to

1 in the Configuration register. Enter hardware-standby

by pulling STBY low. Software-standby mode disables

the ADC and reduces the supply current to approximately

4µA. During either software or hardware standby, data is

retained in memory. During hardware standby, the SMBus

interface is inactive. During software standby, the SMBus

interface is active and listening for commands. The time-

out is enabled if a START condition is recognized on

SMBus. Activity on the SMBus causes the supply current

to increase. If a standby command is received while a

conversion is in progress, the conversion cycle is inter-

rupted, and the temperature registers are not updated.

The previous data is not changed and remains available.

Operating-Current Calculation

The MAX6581 operates at different operating-current

levels depending on how many external channels are in

use and how many of those are in resistance cancellation

(RC) mode. The average operating current is:

AV CC1 CC2

NR NR

N 1 2N

II I

N 2N 1 N 2N 1

+×

= +×

+× + +× +

where:

NN = the number of remote channels that are operating

in normal mode.

NR = the number of remote channels that are in RC mode.

IAV = the average operating power-supply current over a

complete series of conversions.

ICC1 = the average operating power-supply current

during a conversion in normal mode.

ICC2 = the average operating power-supply current

during a conversion in RC mode.

PIN NAME FUNCTION

21 GND Ground

23 DXP1

Combined Current Source and ADC Positive Input for Channel 1 Remote Diode. Connect DXP1 to

the anode of a remote-diode-connected, temperature-sensing transistor. Leave DXP1 unconnected or

connect to DXN1 if a remote diode is not used. Connect a 100pF capacitor between DXP1 and DXN1

for noise ltering.

24 DXN1

Cathode Input for Channel 1 Remote Diode. Connect the cathode of the channel 1 remote-diode-

connected transistor to DXN1. If the channel 1 remote transistor is a substrate pnp (e.g., on a CPU

die), connect the base of the pnp to DXN1. Leave DXN1 unconnected or connect to DXP1 if a remote

diode is not used. Connect a 100pF capacitor between DXP1 and DXN1 for noise ltering.

— EP Exposed Pad. Connect EP to GND.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Pin Description (continued)

Figure 1. Internal Block Diagram

VCC

DXN2

DXP2

DXN1

DXP1

DXN3

DXP3

DXN4

DXP4

DXN5

DXP5

DXN6

DXP6

LOCAL

TRANSISTOR

SMBCLK SMBDATA

INPUT

BUFFER

REF

COUNTER

SMBus INTERFACE

COUNT

DXN7

DXP7

IRJ

COMMAND BYTE

REMOTE TEMPERATURES

LOCAL TEMPERATURES

STBY

OVERT

ALERT THRESHOLD

OVERT THRESHOLD

ALERT RESPONSE ADDRESS

ALERT

ALARM

ALU

MAX6581

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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SMBus Digital Interface

From a software perspective, the MAX6581 appears

as a series of 8-bit registers that contain temperature-

measurement data, alarm threshold values, and control

bits. A standard SMBus-compatible, 2-wire serial inter-

face is used to read temperature data and write control

bits and alarm threshold data. The same SMBus slave

address also provides access to all functions.

The MAX6581 employs four standard SMBus protocols:

write byte, read byte, send byte, and receive byte (Figure 2).

The shorter receive-byte protocol allows quicker trans-

fers, provided that the correct data register was previously

selected by a read-byte instruction. Use caution with the

shorter protocols in multimaster systems, since a second

master could overwrite the command byte without inform-

ing the first master. Figure 3 is the SMBus write timing

diagram and Figure 4 is the SMBus read timing diagram.

The remote-diode-measurement channels provide

11 bits of data (1 LSB = 0.125°C). The eight most

significant bits (MSBs) can be read from the local tem-

perature and remote temperature registers. The remain-

ing 3 bits for remote can be read from the extended

temperature register. If extended resolution is desired,

the extended-resolution register should be read first. This

prevents the MSBs from being overwritten by new conver-

sion results until they have been read. If the MSBs have

not been read within a SMBus timeout period (nominally

37ms), normal updating continues. Table 1 shows the

main temperature register (high-byte) data format and

Table 2 shows the extended-resolution register (low-byte)

data format.

Figure 2. SMBus Protocols

S ADDRESS WR ACK ACK PDATA ACKCOMMAND

7 BITS 18 BITS8 BITS

SLAVE ADDRESS: EQUIVALENT

TO CHIP-SELECT LINE OF

A 3-WIRE INTERFACE

DATA BYTE: DATA GOES INTO THE REGISTER

SET BY THE COMMAND BYTE (TO SET

THRESHOLDS, CONFIGURATION MASKS, AND

SAMPLING RATE)

WRITE-BYTE FORMAT

S ADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND

7 BITS 7 BITS 8 BITS8 BITS

READ-BYTE FORMAT

SLAVE ADDRESS: EQUIVALENT

TO CHIP SELECT LINE

COMMAND BYTE: SELECTS

WHICH REGISTER YOU ARE

READING FROM

S PADDRESS WR ACK ACKCOMMAND

7 BITS 8 BITS

SEND-BYTE FORMAT

COMMAND BYTE: SENDS COMMAND

WITH NO DATA, USUALLY

USED FOR ONE-SHOT COMMAND

S PADDRESS RD ACK ///DATA

7 BITS 8 BITS

RECEIVE-BYTE FORMAT

DATA BYTE: READS DATA FROM

THE REGISTER COMMANDED

BY THE LAST READ-BYTE OR

WRITE-BYTE TRANSMISSION;

ALSO USED FOR SMBus ALERT

RESPONSE RETURN ADDRESS

SLAVE ADDRESS: REPEATED

DUE TO CHANGE IN DATA-

FLOW DIRECTION

DATA BYTE: READS FROM

THE REGISTER SET BY THE

COMMAND BYTE

S = START CONDITION

P = STOP CONDITION

SHADED = SLAVE TRANSMISSION

/// = NOT ACKNOWLEDGED

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Figure 3. SMBus Write Timing Diagram

Figure 4. Read-Timing Diagram

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

A B C D EF G H I J

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tSU:STO tBUF

L MK

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO SLAVE

H = LSB OF DATA CLOCKED INTO SLAVE

I = SLAVE PULLS DATA LINE LOW

J = ACKNOWLEDGE CLOCKED INTO MASTER

K = ACKNOWLEDGE CLOCK PULSE

L = STOP CONDITION

M = NEW START CONDITION

SMBCLK

A B C D EF G H I

SMBDATA

tSU:STA tHD:STA

tLOW tHIGH

tSU:DAT tHD:DAT tSU:STO tBUF

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Table 1. Main Temperature Register (High-Byte) Data Format

Table 2. Extended-Resolution Temperature Register (Low-Byte) Data Format

X = Don’t care.

TEMPERATURE (°C)

DIGITAL OUTPUT

NORMAL FORMAT

EXTRANGE = 0

EXTENDED FORMAT

EXTRANGE = 1

Diode fault (open or short) 1111 1111 1111 1111

> +254 1111 1111 1111 1111

+254 1111 1110 1111 1111

+191 1011 1111 1111 1111

+190 1011 1110 1111 1110

+125 0111 1101 1011 1101

+85 0101 0101 1001 0101

+25 0001 1001 0101 1001

0 0000 0000 0100 0000

-1 0000 0000 0011 1111

-40 0000 0000 0001 1000

-63 0000 0000 0000 0001

-64 0000 0000 0000 0000

< -64 0000 0000 0000 0000

TEMPERATURE (°C) DIGITAL OUTPUT

0 000X XXXX

+0.125 001X XXXX

+0.250 010X XXXX

+0.375 011X XXXX

+0.500 100X XXXX

+0.625 101X XXXX

+0.750 110X XXXX

+0.875 111X XXXX

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Table 3. Command Byte Register Bit Assignment

(HEX)

POR

VALUE

(HEX)

READ/

WRITE DESCRIPTION

Remote 1 01 00 R Read channel 1 remote temperature

Remote 2 02 00 R Read channel 2 remote temperature

Remote 3 03 00 R Read channel 3 remote temperature

Remote 4 04 00 R Read channel 4 remote temperature

Remote 5 05 00 R Read channel 5 remote temperature

Remote 6 06 00 R Read channel 6 remote temperature

Local 07 00 R Read local temperature

Remote 7 08 00 R Read channel 7 remote temperature

Remote 1 Extended

Bits* 09 00 R Read channel 1 remote-diode extended temperature

Manufacturer ID 0A 4D R Read manufacturer ID

Revision ID 0F 00 R Read revision ID

Remote 1 ALERT High

Limit 11 7F R/W Read/write channel 1 remote-diode alert high-temperature

threshold limit

Remote 2 ALERT High

Limit 12 7F R/W Read/write channel 2 remote-diode alert high-temperature

threshold limit

Remote 3 ALERT High

Limit 13 64 R/W Read/write channel 3 remote-diode alert high-temperature

threshold limit

Remote 4 ALERT High

Limit 14 64 R/W Read/write channel 4 remote-diode alert high-temperature

threshold limit

Remote 5 ALERT High

Limit 15 64 R/W Read/write channel 5 remote-diode alert high-temperature

threshold limit

Remote 6 ALERT High

Limit 16 64 R/W Read/write channel 6 remote-diode alert high-temperature

threshold limit

Local ALERT High Limit 17 5A R/W Read/write local-diode alert high-temperature threshold limit

Remote 7 ALERT High

Limit 18 64 R/W Read/write channel 7 remote-diode alert high-temperature

threshold limit

Local OVERT High Limit 20 50 R/W Read/write channel local-diode overtemperature threshold limit

Remote 1 OVERT High

Limit 21 6E R/W Read/write channel 1 remote-diode overtemperature threshold limit

Remote 2 OVERT High

Limit 22 6E R/W Read/write channel 2 remote-diode overtemperature threshold limit

Remote 3 OVERT High

Limit 23 6E R/W Read/write channel 3 remote-diode overtemperature threshold limit

Remote 4 OVERT High

Limit 24 7F R/W Read/write channel 4 remote-diode overtemperature threshold limit

Remote 5 OVERT High

Limit 25 5A R/W Read/write channel 5 remote-diode overtemperature threshold limit

Remote 6 OVERT High

Limit 26 5A R/W Read/write channel 6 remote-diode overtemperature threshold limit

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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│

Table 3. Command Byte Register Bit Assignment (continued)

*Duplicate entries.

(HEX)

POR

VALUE

(HEX)

READ/

WRITE DESCRIPTION

Remote 7 OVERT High

Limit 27 5A R/W Read/write channel 7 remote-diode overtemperature threshold limit

ALERT Low Limits (all

channels) 30 00 R/W Read/write all channels alert low-temperature threshold limit

Conguration 41 00 R/W Read/write conguration

ALERT Mask 42 00 R/W Read/write ALERT mask

OVERT Mask 43 00 R/W Read/write OVERT mask

ALERT High Status 44 00 R Read ALERT high status

OVERT Status 45 00 R Read OVERT status

Diode Fault Status 46 00 R Read diode fault status

ALERT Low Status 47 00 R Read ALERT low status

ALERT Low Disable 48 FF R/W Read/write ALERT low disable

Resistance Cancellation 4A 00 R/W Read/write resistance cancellation enable bits (1 = On, 0 = O󰀨)

Transistor Ideality 4B 00 R/W Read/write ideality value for remote-sense transistor

Ideality Select 4C 00 R/W Read/write ideality value selection bits (1 = selected transistor

ideality, 0 = 1.008)

O󰀨set 4D 00 R/W Read/write temperature o󰀨set value

O󰀨set Select 4E 00 R/W Read/write o󰀨set value selection bits (1 = value in O󰀨set register,

0 = 0)

Remote 1 Extended

Bits* 51 00 R Read channel 1 remote extended temperature

Remote 2 Extended Bits 52 00 R Read channel 2 remote extended temperature

Remote 3 Extended Bits 53 00 R Read channel 3 remote extended temperature

Remote 4 Extended Bits 54 00 R Read channel 4 remote extended temperature

Remote 5 Extended Bits 55 00 R Read channel 5 remote extended temperature

Remote 6 Extended Bits 56 00 R Read channel 6 remote extended temperature

Local Extended Bits 57 00 R Read local channel extended temperature

Remote 7 Extended Bits 58 00 R Read channel 7 remote extended temperature

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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│

Diode Fault Detection

If a channel’s input DXP_ and DXN_ are left open or are

shorted, the MAX6581 detects a diode fault. An open

diode fault does not cause either ALERT or OVERT to

assert. A bit in the status register for the corresponding

channel is set to 1 and the temperature data for the chan-

nel is stored as all 1s (FFh). It takes approximately 4ms

for the MAX6581 to detect a diode fault. Once a diode

fault is detected, the MAX6581 goes to the next channel

in the conversion sequence.

Alarm Threshold Registers

There are 17 alarm threshold registers that store over-

temperature and undertemperature ALERT and OVERT

threshold values. Nine of these registers are dedicated

to storing one local alert overtemperature threshold limit,

seven remote alert overtemperature threshold limits, and

one shared alert undertemperature temperature thresh-

old limit (see the ALERT Interrupt Mode section). The

remaining eight registers are dedicated to storing one

local overtemperature threshold limit and seven remote

channels to store overtemperature threshold limits (see

the OVERT Overtemperature Alarms section). Access to

these registers is provided through the SMBus interface.

ALERT Interrupt Mode

ALERT interrupts occur when the internal or external tem-

perature reading exceeds a high-temperature limit (user

programmable) or a low-temperature limit. The ALERT

interrupt output signal can be cleared by reading the sta-

tus register(s) associated with the fault(s) or by success-

fully responding to an alert response address transmis-

sion by the master. In both cases, the alert is cleared but

is reasserted at the end of the next conversion if the fault

condition still exists. The interrupt does not halt automatic

conversions. The ALERT output is open-drain so that

multiple devices can share a common interrupt line. All

ALERT interrupts can be masked using the ALERT Mask

in Table 3.

ALERT Responses Address

The SMBus alert response interrupt pointer provides

quick fault identification for simple slave devices that lack

the complex logic necessary to be a bus master. Upon

receiving an interrupt signal, the host master can broad-

cast a receive-byte transmission to the alert response

slave address (19h). Then, any slave device that gener-

ated an interrupt attempts to identify itself by putting its

own address on the bus.

The alert response can activate several different slave

devices simultaneously, similar to the I2C general call. If

more than one slave attempts to respond, bus arbitration

rules apply, and the device with the lower address code

wins. The losing device does not generate an acknowl-

edgment and continues to hold the ALERT line low until

cleared (the conditions for clearing an alert vary depending

on the type of slave device.) Successful completion of the

alert response protocol clears the output latch. If the condi-

tion that caused the alert still exists, the MAX6581 reas-

serts the ALERT interrupt at the end of the next conversion.

OVERT Overtemperature Alarms

The MAX6581 has eight overtemperature registers that

store alarm threshold data for the OVERT output. OVERT

is asserted when a channel’s measured temperature is

greater than the value stored in the corresponding thresh-

old register. OVERT remains asserted until the tempera-

ture drops below the programmed threshold minus 4°C

hysteresis. An overtemperature output can be used to

activate a cooling fan, send a warning, initiate clock throt-

tling, or trigger a system shutdown to prevent component

damage. See Table 3 for the POR state of the overtem-

perature threshold registers.

Command Byte Register Functions

The 8-bit Command Byte register (Table 3) is the master

index that points to the various other registers within the

MAX6581. This register’s POR state is 0000 0000 (00h).

Conguration Register (41h)

The Configuration register (Table 4) has several

functions. Bit 7 (MSB) is used to put the MAX6581

either in software-standby mode (STOP) or continuous-

conversion mode. Bit 6 resets all registers to their POR

conditions and then clears itself. Bit 5 disables the SMBus

timeout. Bit 1 sets the extended range of the remote tem-

perature diodes. The remaining bits of the Configuration

0000 0000 (00h).

ALERT Mask Register (42h)

The ALERT Mask register functions are described

in Table 5. Bits [7:0] are used to mask the ALERT

interrupt output. Bit 6 masks the local alert interrupt and

the remaining bits mask the remote alert interrupts. The

power-up state of this register is 0000 0000 (00h).

OVERT Mask Register (43h)

Table 6 describes the OVERT Mask register. Bit 7 and

the remaining bits mask the OVERT interrupt output for

all channels. The power-up state of this register is 0000

0000 (00h).

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Table 4. Configuration Register (41h)

Table 5. ALERT Mask Register (42h)

Table 6. OVERT Mask Register (43h)

BIT NAME POR

VALUE FUNCTION

7 (MSB) STOP 0 Standby-Mode Control Bit. If STOP is set to logic 1, the MAX6581 stops converting and

enters standby mode.

6 POR 0 Reset Bit. Set to logic 1 to put the device into its power-on state. This bit is self-clearing.

5TIMEOUT 0 Timeout Enable Bit. Set to logic 0 to enable SMBus timeout.

4 RESERVED 0 Reserved. Must be set to 0.

3 RESERVED 0 Reserved. Must be set to 0.

2 RESERVED 0 Reserved. Must be set to 0.

1 EXTRANGE 0 Extended-Range Enable Bit. Set bit 1 to logic 1 to set the temperature and limit data

range to -64°C to +191°C. Set bit 1 to logic 0 to set the range to 0°C to +255°C.

0 RESERVED 0 Reserved. Must be set to 0.

BIT NAME POR

VALUE FUNCTION

7 (MSB) Mask ALERT 7 0 Channel 7 Alert Mask. Set to logic 1 to mask channel 7 ALERT.

6Mask Local

ALERT 0 Local Alert Mask. Set to logic 1 to mask local channel ALERT.

5 Mask ALERT 6 0 Channel 6 Alert Mask. Set to logic 1 to mask channel 6 ALERT.

4 Mask ALERT 5 0 Channel 5 Alert Mask. Set to logic 1 to mask channel 5 ALERT.

3 Mask ALERT 4 0 Channel 4 Alert Mask. Set to logic 1 to mask channel 4 ALERT.

2 Mask ALERT 3 0 Channel 3 Alert Mask. Set to logic 1 to mask channel 3 ALERT.

1 Mask ALERT 2 0 Channel 2 Alert Mask. Set to logic 1 to mask channel 2 ALERT.

0 Mask ALERT 1 0 Channel 1 Alert Mask. Set to logic 1 to mask channel 1 ALERT.

BIT NAME POR

VALUE FUNCTION

7 (MSB) Mask Local

OVERT 0 Local Overt Mask. Set to logic 1 to mask local channel OVERT.

6 Mask OVERT 7 0 Channel 7 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 7 OVERT.

5 Mask OVERT 6 0 Channel 6 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 6 OVERT.

4 Mask OVERT 5 0 Channel 5 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 5 OVERT.

3 Mask OVERT 4 0 Channel 4 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 4 OVERT.

2 Mask OVERT 3 0 Channel 3 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 3 OVERT.

1 Mask OVERT 2 0 Channel 2 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 2 OVERT.

0 Mask OVERT 1 0 Channel 1 Remote-Diode OVERT Mask Bit. Set to logic 1 to mask channel 1 OVERT.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Status Register Functions

There are four status registers (see Tables 7–10). The

ALERT High Status register indicates whether a mea-

sured local or remote temperature has exceeded the

associated threshold limit set in an ALERT High Limit

a measured temperature has exceeded the associated

threshold limit set in an OVERT High Limit register. The

Diode Fault Status register indicates whether there is a

diode fault (open or short) in any of the remote-sensing

channels. The ALERT Low Status register indicates

whether the measured temperature has fallen below the

threshold limit set in the ALERT Low Limits register for the

local or remote-sensing diodes.

Bits in the alert status registers are cleared by a success-

ful read, but set again after the next conversion unless

the fault is corrected, either by a drop in the measured

temperature or a change in the threshold temperature.

The ALERT interrupt output follows the status flag bit.

Once the ALERT output is asserted, it can be deasserted

by either reading the ALERT High Status register or by

successfully responding to an alert response address. In

both cases, the alert is cleared even if the fault condition

exists, but the ALERT output reasserts at the end of the

next conversion.

The bits indicating OVERT faults clear only when the

measured temperature drops below the temperature

threshold minus the hysteresis value (4°C), or when the

trip temperature is set to a value at least 4°C above the

current temperature.

Table 7. ALERT High Status Register (44h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Remote ALERT

High 7 0

Channel 7 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 7

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 7 ALERT High Limit register.

6Local ALERT

High 0Local Channel High-Alert Bit. This bit is set to logic 1 when the local temperature

exceeds the temperature threshold limit in the Local ALERT High Limit register.

5Remote ALERT

High 6 0

Channel 6 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 6

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 6 ALERT High Limit register.

4Remote ALERT

High 5 0

Channel 5 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 5

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 5 ALERT High Limit register.

3Remote ALERT

High 4 0

Channel 4 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 4

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 4 ALERT High Limit register.

2Remote ALERT

High 3 0

Channel 3 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 3

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 3 ALERT High Limit register.

1Remote ALERT

High 2 0

Channel 2 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 2

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 2 ALERT High Limit register.

0Remote ALERT

High 1 0

Channel 1 Remote-Diode High-Alert Bit. This bit is set to logic 1 when the channel 1

remote-diode temperature exceeds the programmed temperature threshold limit in the

Remote 1 ALERT High Limit register.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Table 8. OVERT Status Register (45h)

Table 9. Diode Fault Status Register (46h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Local OVERT 0

Local Channel Overtemperature Status Bit. This bit is set to logic 1 when the local

temperature exceeds the temperature threshold limit in the Local OVERT High Limit

6 Remote OVERT 7 0

Channel 7 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 7 remote-diode temperature exceeds the temperature threshold limit in the

Remote 7 OVERT High Limit register.

5 Remote OVERT 6 0

Channel 6 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 6 remote-diode temperature exceeds the temperature threshold limit in the

Remote 6 OVERT High Limit register.

4 Remote OVERT 5 0

Channel 5 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 5 remote-diode temperature exceeds the temperature threshold limit in the

Remote 5 OVERT High Limit register.

3 Remote OVERT 4 0

Channel 4 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 4 remote-diode temperature exceeds the temperature threshold limit in the

Remote 4 OVERT High Limit register.

2 Remote OVERT 3 0

Channel 3 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 3 remote-diode temperature exceeds the temperature threshold limit in the

Remote 3 OVERT High Limit register.

1 Remote OVERT 2 0

Channel 2 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 2 remote-diode temperature exceeds the temperature threshold limit in the

Remote 2 OVERT High Limit register.

0 Remote OVERT 1 0

Channel 1 Remote-Diode Overtemperature Status Bit. This bit is set to logic 1 when

the channel 1 remote-diode temperature exceeds the temperature threshold limit in the

Remote 1 OVERT High Limit register.

BIT NAME POR

STATE FUNCTION

7 (MSB) RESERVED 0 —

6 Diode Fault 7 0 Channel 7 Remote-Diode Fault Bit. This bit is set to 1 when DXP7 and DXN7 are open

circuit or when DXP7 is connected to VCC.

5 Diode Fault 6 0 Channel 6 Remote-Diode Fault Bit. This bit is set to 1 when DXP6 and DXN6 are open

circuit or when DXP6 is connected to VCC.

4 Diode Fault 5 0 Channel 5 Remote-Diode Fault Bit. This bit is set to 1 when DXP5 and DXN5 are open

circuit or when DXP5 is connected to VCC.

3 Diode Fault 4 0 Channel 4 Remote-Diode Fault Bit. This bit is set to 1 when DXP4 and DXN4 are open

circuit or when DXP4 is connected to VCC.

2 Diode Fault 3 0 Channel 3 Remote-Diode Fault Bit. This bit is set to 1 when DXP3 and DXN3 are open

circuit or when DXP3 is connected to VCC.

1 Diode Fault 2 0 Channel 2 Remote-Diode Fault Bit. This bit is set to 1 when DXP2 and DXN2 are open

circuit or when DXP2 is connected to VCC.

0 Diode Fault 1 0 Channel 1 Remote-Diode Fault Bit. This bit is set to 1 when DXP1 and DXN1 are open

circuit or when DXP1 is connected to VCC.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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E󰀨ect of Ideality Factor

The accuracy of the remote temperature measurements

depends on the ideality factor (n) of the remote “diode”

(actually a transistor). The default value for the MAX6581

is n = 1.008 (channels 1–7). A thermal diode on the

substrate of an IC is normally a pnp with the base and

emitter brought out and the collector (diode connection)

grounded. DXP_ must be connected to the anode (emit-

ter) and DXN_ must be connected to the cathode (base)

of this pnp. If a sense transistor with an ideality factor

other than 1.008 is used, the output data is different

from the data obtained with the optimum ideality factor. If

necessary, a different ideality factor value can be chosen

using the Transistor Ideality register (see Table 11). The

Ideality Select register allows each channel to have the

default ideality of 1.008 or the value programmed in the

Transistor Ideality register.

Table 10. ALERT Low Status Register (47h)

BIT NAME POR

STATE FUNCTION

7 (MSB) Remote ALERT

Low 7 0

Channel 7 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 7

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 7 ALERT Low Limit register.

6 Local ALERT Low 0

Local Channel Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the local

channel remote-diode temperature falls below the programmed temperature threshold

limit in the Local ALERT Low Limit register.

5Remote ALERT

Low 6 0

Channel 6 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 6

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 6 ALERT Low Limit register.

4Remote ALERT

Low 5 0

Channel 5 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 5

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 5 ALERT Low Limit register.

3Remote ALERT

Low 4 0

Channel 4 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 4

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 4 ALERT Low Limit register.

2Remote ALERT

Low 3 0

Channel 3 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 3

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 3 ALERT Low Limit register.

1Remote ALERT

Low 2 0

Channel 2 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 2

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 2 ALERT Low Limit register.

0Remote ALERT

Low 1 0

Channel 1 Remote-Diode Low-Alert Bit. This bit is set to logic 1 when the channel 1

remote-diode temperature falls below the programmed temperature threshold limit in

the Remote 1 ALERT Low Limit register.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Table 11. Transistor Ideality Register

X = Don’t care.

FACTOR HEX

0x4B

X X X 0 0 0 0 0 .999 0x00

X X X 0 0 0 0 1 1.000 0x01

X X X 0 0 0 1 0 1.001 0x02

X X X 0 0 0 1 1 1.002 0x03

X X X 0 0 1 0 0 1.003 0x04

X X X 0 0 1 0 1 1.004 0x05

X X X 0 0 1 1 0 1.005 0x06

X X X 0 0 1 1 1 1.006 0x07

X X X 0 1 0 0 0 1.007 0x08

X X X 0 1 0 0 1 1.008 0x09

X X X 0 1 0 1 0 1.009 0x0A

X X X 0 1 0 1 1 1.010 0x0B

X X X 0 1 1 0 0 1.011 0x0C

X X X 0 1 1 0 1 1.012 0x0D

X X X 0 1 1 1 0 1.013 0x0E

X X X 0 1 1 1 1 1.014 0x0F

X X X 1 0 0 0 0 1.015 0x10

X X X 1 0 0 0 1 1.016 0x11

X X X 1 0 0 1 0 1.017 0x12

X X X 1 0 0 1 1 1.018 0x13

X X X 1 0 1 0 0 1.019 0x14

X X X 1 0 1 0 1 1.020 0x15

X X X 1 0 1 1 0 1.021 0x16

X X X 1 0 1 1 1 1.022 0x17

X X X 1 1 0 0 0 1.023 0x18

X X X 1 1 0 0 1 1.024 0x19

X X X 1 1 0 1 0 1.025 0x1A

X X X 1 1 0 1 1 1.026 0x1B

X X X 1 1 1 0 0 1.027 0x1C

X X X 1 1 1 0 1 1.028 0x1D

X X X 1 1 1 1 0 1.029 0x1E

X X X 1 1 1 1 1 1.030 0x1F

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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│

Series-Resistance Cancellation

Some thermal diodes on high-power ICs have exces-

sive series resistance that can cause temperature-mea-

surement errors when used with conventional remote-

temperature sensors. Channels 1–7 of the MAX6581

have a series-resistance cancellation feature (enabled

by bits [7:0] of the Resistance Cancellation register)

that eliminates the effect of diode series resistance and

interconnection resistance. Set these bits to 1 if the series

resistance is large enough to affect the accuracy of the

channels. The series-resistance cancellation function

increases the conversion time for the remote channels by

125ms (typ). This feature cancels the bulk resistance of

the sensor and any other resistance in series (e.g., wire,

contact resistance, etc.). The cancellation range is from

0Ω to 100Ω.

Table 12. Resistance Cancellation Register (4Ah)

X = Don’t care.

BIT NAME POR

STATE FUNCTION

7 (MSB) X 0 —

6Resistance

Cancellation 7 0Channel 7 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

5Resistance

Cancellation 6 0Channel 6 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

4Resistance

Cancellation 5 0Channel 5 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

3Resistance

Cancellation 4 0Channel 4 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

2Resistance

Cancellation 3 0Channel 3 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

1Resistance

Cancellation 2 0Channel 2 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

0Resistance

Cancellation 1 0Channel 1 Resistance Cancellation Enable Bit. Set this bit to logic 1 to enable

resistance cancellation. Set this bit to logic 0 to disable resistance cancellation.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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O󰀨set and O󰀨set Select Registers

(4Dh and 4Eh)

To compensate for remote temperature reporting errors

due to issues with the board layout, the Offset register

(4Dh) and Offset Enable register (4Eh) allow for a two’s-

complement value to be added to the final ADC conver-

sion output. The Offset register (4Dh) contains the value

for the shared temperature offset (i.e., the same offset is

applied to all selected remote channels) and has a pro-

grammable ±31.75°C range.

The Offset Enable register (4Eh) allows the offset to be

selectively enabled for each remote channel.

If EXTRANGE = 0, the minimum digital output values are

clamped at 00h (0°C), regardless of any applied offset.

If EXTRANGE = 1, the maximum digital output values

are clamped at FFh (+191°C), regardless of any applied

offset.

Table 13. Offset Register (4Dh)

Table 14. Offset Select Register (4Eh)

BIT NAME POR

STATE FUNCTION

7 (MSB) SIGN 0 Digital O󰀨set Polarity

6 16°C 0 Digital O󰀨set (Weighted)

5 8°C 0 Digital O󰀨set (Weighted)

4 4°C 0 Digital O󰀨set (Weighted)

3 2°C 0 Digital O󰀨set (Weighted)

2 1°C 0 Digital O󰀨set (Weighted)

1 0.5°C 0 Digital O󰀨set (Weighted)

0 0.25°C 0 Digital O󰀨set (Weighted)

BIT NAME POR

STATE FUNCTION

7 (MSB) X 0 —

6 Channel 7 0 Remote 7 O󰀨set Enable

5 Channel 6 0 Remote 6 O󰀨set Enable

4 Channel 5 0 Remote 5 O󰀨set Enable

3 Channel 4 0 Remote 4 O󰀨set Enable

2 Channel 3 0 Remote 3 O󰀨set Enable

1 Channel 2 0 Remote 2 O󰀨set Enable

0 Channel 1 0 Remote 1 O󰀨set Enable

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

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Applications Information

Remote-Diode Selection

The MAX6581 directly measures the die temperature of

CPUs and other ICs that have on-chip temperature-sensing

diodes (see the Typical Application Circuit), or it can measure

the temperature of a discrete diode-connected transistor.

Discrete Remote Diodes

When the remote-sensing diode is a discrete transistor,

its collector and base must be connected together. Table

13 lists examples of discrete transistors that are appropriate for

use with the MAX6581. The transistor must be a small-

signal type with a relatively high forward voltage;

otherwise, the A/D input-voltage range can be violated.

The forward voltage at the highest expected temperature

must be greater than 0.25V at 10µA, and at the lowest

expected temperature the forward voltage must be less

than 0.95V at 100µA. Large power transistors must not be

used. Also, ensure that the base resistance is less than

100Ω. Tight specifications for forward-current gain (e.g.,

50 < ß < 150) indicate that the manufacturer has good

process controls and that the devices have consistent

VBE characteristics. Manufacturers of discrete transis-

tors do not normally specify or guarantee ideality factor.

This normally is not a problem since good-quality discrete

transistors tend to have ideality factors that fall within a

relatively narrow range. Variations in remote temperature

readings of less than ±2°C with a variety of discrete tran-

sistors have been observed. However, it is good design

practice to verify good consistency of temperature read-

ings with several discrete transistors from any supplier

under consideration.

Unused Diode Channels

If one or more of the remote-diode channels is not needed,

disconnect the DXP_ and DXN_ inputs for that channel, or

connect the DXP_ to the corresponding DXN_. The status

channel is ignored during the temperature-measurement

sequence. It is also good practice to mask any unused

channels immediately upon power-up by setting the appro-

priate bits in the ALERT Mask and OVERT Mask registers.

Table 15. Remote Sensors Transistor Suppliers (for Channels 1–7)

Note: Discrete transistors must be diode connected (base shorted to collector).

SUPPLIER MODEL NO.

PNP NPN

Central Semiconductor Corp. (USA) CMPT3906

2N3906

CMPT3904

2N3904

Fairchild Semiconductor (USA) MMBT3906

2N3906 2N3904

Inneon (Germany) SMBT3906 —

ON Semiconductor (USA) MMBT3906

2N3906 2N3904

ROHM Semiconductor (USA) SST3906 SST3904

Samsung (Korea) KST3906-TF KST3904-TF

Siemens (Germany) SMBT3906 SMBT3904

Zetex (England) FMMT3906CT-ND FMMT3904CT-ND

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

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Thermal Mass and Self-Heating

When sensing local temperature, the MAX6581 measures

the temperature of the PCB to which it is soldered. The

leads provide a good thermal path between the PCB

traces and the die. As with all IC temperature sensors,

thermal conductivity between the die and the ambient air

is poor by comparison, making air-temperature measure-

ments impractical. Since the thermal mass of the PCB is

far greater than that of the MAX6581, the device follows

temperature changes on the PCB with little or no perceiv-

able delay. When measuring the temperature of a CPU,

or other IC with an on-chip sense junction, thermal mass

has virtually no effect; the measured temperature of the

junction tracks the actual temperature within a conversion

cycle. When measuring temperature with discrete remote

transistors, the best thermal-response times are obtained

with transistors in small packages (i.e., SOT23 or SC70).

Take care to account for thermal gradients between the

heat source and the sensor, and ensure that stray air

currents across the sensor package do not interfere with

measurement accuracy. Self-heating does not significantly

affect measurement accuracy. Remote-sensor self-heating

due to the diode current source is negligible.

ADC Noise Filtering

The integrating ADC has good noise rejection for

low-frequency signals, such as power-supply hum. In

environments with significant high-frequency EMI,

connect an external 100pF capacitor between DXP_ and

DXN_. Larger capacitor values can be used for added

filtering; however, it can introduce errors due to the rise

time of the switched current source. High-frequency noise

reduction is needed for high-accuracy remote measure-

ments. Noise can be reduced with careful PCB layout as

discussed in the PCB Layout section.

Slave Address

The slave address for the MAX6581 is shown in Table 16.

PCB Layout

Follow the guidelines below to reduce the measurement

error when measuring remote temperature:

1) Place the MAX6581 as close as possible to the remote

diode. In noisy environments, such as a computer

motherboard, this distance is typically 4in to 8in. This

length can be increased if the worst-noise sources

are avoided. Noise sources include displays, clock

generators, memory buses, and PCI buses.

2) Do not route the DXP_–DXN_ lines next to the deflec-

tion coils of a CRT. Also, do not route the traces across

fast digital signals, which can easily introduce +30°C

error, even with good filtering.

3) Route the DXP_ and DXN_ traces in parallel and

in close proximity to each other. Each parallel pair

of traces should go to a remote diode. Route these

traces away from any higher voltage traces, such as

+12V DC. Leakage currents from PCB contamination

must be dealt with carefully since a 20MΩ leakage

path from DXP_ to ground causes approximately +1°C

error. If high-voltage traces are unavoidable, connect

guard traces to GND on either side of the DXP_–DXN_

traces (Figure 5).

4) Route through as few vias and crossunders as pos-

sible to minimize copper/solder thermocouple effects.

5) Use wide traces when possible (5-mil to 10-mil traces

are typical). Be aware of the effect of trace resistance

on temperature readings when using long, narrow

traces.

6) When the power supply is noisy, add a resistor (up to

47Ω) in series with VCC.

Table 16. Slave Address

Figure 5. Recommended DXP_–DXN_ PCB Traces. The two

outer guard traces are recommended if high-voltage traces are

near the DXN_ and DXP_ traces.

DEVICE ADDRESS

A7 A6 A5 A4 A3 A2 A1 A0

1 0 0 1 1 0 1 R/W

5–10 mils

MINIMUM

5–10 mils

GND

DXP_

DXN_

GND

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Twisted-Pair and Shielded Cables

Use a twisted-pair cable to connect the remote sensor for

remote-sensor distances longer than 8in or in very noisy

environments. Twisted-pair cable lengths can be between

6ft and 12ft before noise introduces excessive errors. For

longer distances, the best solution is a shielded twisted

pair such as those used for audio microphones. For

example, Belden #8451 works well for distances up to

100ft in a noisy environment. At the device, connect the

twisted-pair cables to DXP_ and DXN_ and the shielded

cable to GND. Leave the shielded cable unconnected at

the remote sensor. For very long cable runs, the cable’s

parasitic capacitance often provides noise filtering;

therefore the 100pF capacitor can often be removed or

reduced in value. Cable resistance also affects remote-

sensor accuracy. For every 1Ω of series resistance, the

error is approximately +0.5°C.

DXP2 ALERT

VCC

OVERT

STBY

DXP7

I.C.

24 23 22 21 20 19

DXN2

DXP1 N.C. GND

+3.3V

SMBCLK SMBDATA

CPU

FPGA

ASIC

100pF

DXP3

DXN3

DXN1

DXN7

100pF

100pF100pF

10 11

DXN6 DXP6

87 9

DXP5DXN4 DXN5

4.7kΩ4.7kΩ4.7kΩ4.7kΩ

TO µP

0.1µF

DXP4

N.C.

MAX6581

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Typical Application Circuit

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

24 TQFN-EP T2444+4 21-0139 90-0022

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Package Information

For the latest package outline information and land patterns

(footprints), go to www.maximintegrated.com/packages. Note

that a “+”, “#”, or “-” in the package code indicates RoHS status

only. Package drawings may show a different suffix character, but

the drawing pertains to the package regardless of RoHS status.

Chip Information

PROCESS: BiCMOS

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 8/10 Initial release —

1 2/13

Added the Package Thermal Characteristics section; updated Table 1; added 58h

section and related bit tables

2, 12, 14,

2 2/17 Updated Unused Diode Channels section 23

3 4/17 Updated Table 1 12

4 2/19 Updated OVERT Mask Register (43h) section, Table 6, and Table 8 15, 16, 18

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses

are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)

shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

MAX6581 ±1°C Accurate 8-Channel Temperature Sensor

│

Revision History

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