LM75BIMMX-3 - National Semiconductor

General Description

The LM75 temperature sensor includes a delta-sigma

analog-to-digital converter, and a digital overtempera-

ture detector. The host can query the LM75 through its

I2C interface to read temperature at any time. The

open-drain overtemperature output (OS) sinks current

when the programmable temperature limit is exceeded.

The OS output operates in either of two modes, com-

parator or interrupt. The host controls the temperature

at which the alarm is asserted (TOS) and the hysteresis

temperature below which the alarm condition is not

valid (THYST). Also, the LM75’s TOS and THYST regis-

ters can be read by the host. The address of the LM75

is set with three pins to allow multiple devices to work

on the same bus. Power-up is in comparator mode, with

defaults of TOS = +80°C and THYST = +75°C. The 3.0V

to 5.5V supply voltage range, low supply current, and

I2C interface make the LM75 ideal for many applica-

tions in thermal management and protection.

Applications

Thermal System Management

Thermal Protection

Test Equipment

Computers and Office Electronics

Features

♦SO (SOP) and µMAX®(µSOP) Packages

♦I2C Bus Interface

♦Separate Open-Drain OS Output Operates as

Interrupt or Comparator/Thermostat Input

♦Register Readback Capability

♦Power-Up Defaults Permit Stand-Alone Operation

as a Thermostat

♦3.0V to 5.5V Supply Voltage

♦Low Operating Supply Current 250µA (typ), 1mA

(max)

♦4µA (typ) Shutdown Mode Minimizes Power

Consumption

♦Up to Eight LM75s Can Be Connected to a Single

Bus

♦Pin- and/or Register-Compatible with Improved-

Performance Maxim Sensors Including MAX7500,

MAX6625, MAX6626, DS75LV, and DS7505

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

________________________________________________________________

Maxim Integrated Products

Functional Diagram

Ordering Information/Selector Guide

19-4385; Rev 0; 3/09

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

µMAX is a registered trademark of Maxim Integrated Products, Inc.

Note: Devices are specified over the -55°C to +125°C temperature range and include I

2C noise filter.

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

T&R = Tape and reel.

PART PIN-PACKAGE PKG SUPPLY VOLTAGE (V) TOP MARK

LM75BIM-3+ 8 SO (SOP) Bulk 3.3 LM75BIM-3

LM75BIMX-3+ 8 SO (SOP) T&R 3.3 LM75BIM-3

LM75BIMM-3+ 8 µMAX (µSOP) Bulk 3.3 T01B

LM75BIMMX-3+ 8 µMAX (µSOP) T&R 3.3 T01B

LM75BIM-5+ 8 SO (SOP) Bulk 5.0 LM75BIM-5

LM75BIMX-5+ 8 SO (SOP) T&R 5.0 LM75BIM-5

LM75BIMM-5+ 8 µMAX (µSOP) Bulk 5.0 T00B

LM75BIMMX-5+ 8 µMAX (µSOP) T&R 5.0 T00B

SDA

SCL

+VS = 3.0V to 5.5V

SILICON

BANDGAP

TEMPERATURE

SENSOR

9-BIT DELTA-

SIGMA ADC

CONFIGURATION

TOS SET POINT

THYST SET

POINT REGISTER

SET POINT

COMPARATOR W/

HYSTERESIS

2-WIRE INTERFACE

POINTER

8816 16 16

+VS

A2GND

SCL

SDA

LM75

μMAX (μSOP), SO

TOP VIEW

Pin Configuration

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS (Note 1)

ELECTRICAL CHARACTERISTICS

(+VS= +3.0V to +5.5V, unless otherwise noted. Temperature accuracy specifications apply for +VS= 3.3V for versions with “-3” in

the suffix and for +VS= 5V for versions with “-5” in the suffix. TA= -55°C to +125°C, unless otherwise noted. Typical values are at

+VS= +5V, TA= +25°C.) (Notes 4, 5)

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.

+VSto GND ...........................................................-0.3V to +6.0V

OS, SDA, SCL to GND...........................................-0.3V to +6.0V

All Other Pins to GND.................................-0.3V to (+VS+ 0.3V)

Input Current at Any Pin (Note 2)..........................................5mA

Package Input Current (Note 2)..........................................20mA

OS Output Sink Current ......................................................10mA

Continuous Power Dissipation (TA= +70°C) (Note 3)

8-Pin µMAX (µSOP)

(derate 4.5mW/°C above +70°C)..................................362mW

8-Pin SO (SOP) (derate 5.9mW/°C above +70°C) ........471mW

Junction-to-Case Thermal Resistance (θJC) (Note 3)

8-Pin µMAX (µSOP).......................................................42°C/W

8-Pin SO (SOP)..............................................................40°C/W

Junction-to-Ambient Thermal Resistance (θJA) (Note 3)

8-Pin µMAX (µSOP).....................................................221°C/W

8-Pin SO (SOP)............................................................170°C/W

ESD Protection

Human Body Model (RD= 1.5kΩ, CS= 100pF)

All Pins to GND .................................................................±2kV

Operating Temperature Range .........................-55°C to +125°C

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

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

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

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

-25°C ≤ TA ≤ +100°C -2.0 +2.0

Accuracy (Six-Sigma) -55°C ≤ TA ≤ +125°C -3.0 +3.0 °C

-25°C ≤ TA ≤ +100°C -1.5 +1.5

Accuracy (Three-Sigma) (Note 6) -55°C ≤ TA ≤ +125°C -2.0 +2.0 °C

Resolution 9 Bits

Temperature Conversion Time (Note 7) 100 300 ms

I2C inactive 0.25 0.5 mA

Shutdown mode, +VS = 3V 4

Quiescent Supply Current

Shutdown mode, +VS = 5V 6 µA

+VS Supply Voltage Range 3.0 5.5 V

OS Output Saturation Voltage IOUT = 4.0mA (Note 8) 0.8 V

OS Delay (Note 9) 1 6 Conver-

sions

OS Output Fall Time tOF CL = 400pF, IO = 3mA (Note 10) 250 ns

TOS Default Temperature (Note 11) 80 °C

THYST Default Temperature (Note 11) 75 °C

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifica-

tions do not apply when operating the device beyond its rated operating conditions.

Note 2: When the input voltage (VI) at any pin exceeds the Absolute Maximum Ratings limits (VI< GND, VI> 6V or VI> +VS), the

current at that pin should be limited to 5mA. The 20mA maximum package input current rating limits the number of pins that

can safely exceed the power supplies with an input current of 5mA to four.

Note 3: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a single-

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

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

_______________________________________________________________________________________ 3

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

LOGIC (SDA, SCL, A0, A1, A2)

Input High Voltage V

0.7

0.5 V

Input Low Voltage V

-0.3 +V

0.3 V

Input High Current I

= 5V 0.005 1.0 µA

Input Low Current I

= 0V -1.0 -0.005 µA

Input Capacitance C

All digital inputs 20 pF

Output High Current V

= 5V 10 µA

Output Low Voltage I

= 3mA 0.4 V

C-COMPATIBLE TIMING (Notes 12, 13)

(Clock) SCL Period t

SCL

Bus timeout inactive 2.5 µs

Data In Setup Time to SCL High t

SU:DAT

10% of SDA to 10% of SCL 100 ns

Data Out Stable After SCL Low t

HD:DAT

10% of SCL to 10% of SDA 0 µs

Start Condition Setup Time

(SDA Low to SCL Low) t

SU:STA

90% of SCL to 90% of SDA 100 ns

STOP Condition Hold Time t

HD:STO

100 ns

SDA Time Low for Reset of Serial

Interface t

TIMEOUT

(Note 14) 75 325 ms

ELECTRICAL CHARACTERISTICS (continued)

(+VS= +3.0V to +5.5V, unless otherwise noted. Temperature accuracy specifications apply for +VS= 3.3V for versions with “-3” in

the suffix and for +VS= 5V for versions with “-5” in the suffix. TA= -55°C to +125°C, unless otherwise noted. Typical values are at

+VS= +5V, TA= +25°C.) (Notes 4, 5)

Note 4: All parts operate properly over the 3V to 5.5V supply voltage range. The devices are tested and specified for rated

accuracy at their nominal supply voltage.

Note 5: All parameters are measured at TA= +25°C. Values over the temperature range are guaranteed by design.

Note 6: There is no industry-wide standard for temperature accuracy specifications. Maxim’s standard is six-sigma. The three-

sigma specification is included to allow easier comparison to products built by manufacturers who use different standards.

Note 7: This specification indicates how often temperature data is updated. The devices can be read at any time without regard to

conversion state, while yielding the last conversion result.

Note 8: For best accuracy, minimize output loading. Higher sink currents can affect sensor accuracy due to internal heating.

Note 9: OS delay is user programmable up to 6 over-limit conversions before OS is set to minimize false tripping in noisy environ-

ments.

Note 10: Guaranteed by design.

Note 11: Default values set at power-up.

Note 12: All timing specifications are guaranteed by design.

Note 13: Unless otherwise noted, these specifications apply for +VS= +5VDC for LM75BIM-5 and LM75BIMM-5 and +VS=

+3.3VDC for LM75BIM-3 and LM75BIMM-3. CL(load capacitance) on output lines = 80pF, unless otherwise specified.

The switching characteristics of the LM75 fully meet or exceed the published specifications of the I2C bus. These parame-

ters are the timing relationships between SCL and SDA signals related to the LM75. They are not I2C bus specifications.

Note 14: Holding the SDA line low for a time greater than tTIMEOUT causes the device to reset SDA to the IDLE state of the

serial bus communication (SDA set high).

QUIESCENT SUPPLY CURRENT

vs. TEMPERATURE

LM75 toc01

TEMPERATURE (°C)

QUIESCENT SUPPLY CURRENT (μA)

9565355-25

240

250

260

270

280

290

300

230

-55 125

+VS = +5V

+VS = +3V

SHUTDOWN SUPPLY CURRENT (μA)

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

LM75 toc02

TEMPERATURE (°C)

9565355-25-55 125

+VS = +5V

+VS = +3V

ACCURACY vs. TEMPERATURE

ACCURACY (°C)

-1.5

-1.0

-0.5

0.5

1.0

1.5

2.0

-2.0

LM75 toc03

TEMPERATURE (°C)

9565355-25-55 125

4 TYPICAL PARTS

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

4 _______________________________________________________________________________________

Pin Description

PIN NAME FUNCTION

1 SDA Serial-Data Input/Output Line. Open drain. Connect SDA to a pullup resistor.

2 SCL Serial Clock Input. Open drain. Connect SCL to a pullup resistor.

3 OS Overtemperature Shutdown Output. Open drain. Connect OS to a pullup resistor.

4 GND Ground

5A2

2-Wire Interface Address Input. Connect A2 to GND or +VS to set the desired I2C bus address. Do not

leave unconnected (see Table 1).

6A1

2-Wire Interface Address Input. Connect A1 to GND or +VS to set the desired I2C bus address. Do not

leave unconnected (see Table 1).

7A0

2-Wire Interface Address Input. Connect A0 to GND or +VS to set the desired I2C bus address. Do not

leave unconnected (see Table 1).

8+V

SPositive Supply Voltage Input. Bypass to GND with a 0.1µF bypass capacitor.

Detailed Description

The LM75 temperature sensor measures temperature

and converts the data into digital form using a band-

gap type temperature sensor and a 9-bit delta-sigma

ADC. An I2C-compatible 2-wire serial interface allows

access to conversion results. The LM75 accepts stan-

dard I2C commands to read the data, set the overtem-

perature alarm (OS) trip thresholds, and configure other

characteristics. While reading the Temperature register,

any changes in temperature are ignored until the read

is completed. The Temperature register is updated for

the new temperature measurement upon completion of

the read operation.

OS Output, TOS, and THYST Limits

In comparator mode (see Figure 1), the open-drain OS

output asserts when the temperature rises above the

limit programmed into the TOS register, and becomes

high impedance when the temperature falls below the

limit set in the THYST register. In this mode the LM75

operates as a thermostat, and the OS output can be

used to take action to reduce the temperature (e.g.,

turn on a cooling fan, reduce clock speed, or shut

down the system).

In interrupt mode, exceeding TOS also asserts OS. OS

remains asserted until a read operation is performed on

any of the registers. Once OS has asserted due to

crossing above TOS and is then reset, it is asserted

again only when the temperature drops below THYST.

The output then remains asserted until it is reset by a

read. It is then asserted again if the temperature rises

above TOS, and so on. Putting the LM75 into shutdown

mode also resets OS.

Power-Up and Power-Down

The LM75 powers up to a known state, as indicated in

Table 2. Some of these settings are summarized as fol-

lowing:

• Comparator mode

• TOS = +80°C

• THYST = +75°C

• OS active low

• Command byte pointer = 0x00

C-Compatible Bus Interface

From a software perspective, the LM75 appears as a set

of byte-wide registers that contain temperature data,

alarm threshold values, and control bits. A standard I2C-

compatible, 2-wire serial interface reads temperature

data and writes control bits and alarm threshold data.

Each device responds to its own I2C slave address,

which is selected using A0, A1, and A2. See Table 1.

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

_______________________________________________________________________________________ 5

TOS

THYST

OS OUTPUT

(COMPARATOR MODE)

OS SET ACTIVE LOW

OS OUTPUT

(INTERRUPT MODE)

OS SET ACTIVE LOW READ

OPERATION

READ

OPERATION

READ

OPERATION

TEMPERATURE

Figure 1. OS Output Temperature Response Diagram

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

1 0 0 1 A2A1A0R/W

Table 1. Slave Address

(hex)

POR STATE

(hex) POR STATE (binary) POR STATE (°C) READ/

WRITE

Temperature 00 000X 0000 0000 0XXX XXXX — Read only

Configuration 01 00 0000 0000 — R/W

THYST 02 4B0X 0100 1011 0XXX XXXX 75 R/W

TOS 03 500X 0101 0000 0XXX XXXX 80 R/W

Table 2. Register Functions

X = Don’t care.

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

6 _______________________________________________________________________________________

tBUF

tSU:STO

tHD:STA

tSU:STA

tHD:DAT

tHIGH

tLOW

tSU:DAT

tHD:STA

SCL

SDA

ACKNOWLEDGE

(A)

STOP

CONDITION

(P)

START

CONDITION

(S)

START

CONDITION

(S)

REPEATED START

CONDITION

(SR)

PARAMETERS ARE MEASURED FROM 10% TO 90%.

Figure 2. Serial Bus Timing

UPPER BYTE LOWER BYTE

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Sign bit

1= Negative

0 = Positive

MSB

64°C32°C 16°C 8°C 4°C 2°C 1°C LSB

0.5°C XXXXXXX

Table 3. Temperature, THYST, and TOS Register Definition

X = Don’t care.

DIGITAL OUTPUT

TEMPERATURE (°C) BINARY HEX

+125 0111 1101 0XXX XXXX 7D0X

+25 0001 1001 0XXX XXXX 190X

+0.5 0000 0000 1XXX XXXX 008X

0 0000 0000 0XXX XXXX 000X

-0.5 1111 1111 1XXX XXXX FF8X

-25 1110 0111 0XXX XXXX E70X

-55 1100 1001 0XXX XXXX C90X

Table 4. Temperature Data Output Format

0111 1101 0

0001 1001 0

0000 0000 1

0000 0000 0

1111 1111 1

1110 0111 0

1100 1001 0

-55 -25 -0.5 0 +0.5 +25 +125

LOCAL

BINARY OUTPUT CODE (9MSB)

Figure 3. Temperature-to-Digital Transfer Function

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

_______________________________________________________________________________________ 7

Figure 4. I2C-Compatible Timing Diagram (Read)

ADDRESS

BYTE

ADDRESS BYTE

ADDRESS

BYTE

ADDRESS

BYTE

DATA

BYTE

(a) TYPICAL 2-BYTE READ FROM PRESET POINTER LOCATION SUCH AS TEMP, THIGH, TLOW.

(b) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FOR 2-BYTE REGISTER SUCH AS TEMP, THIGH, TLOW.

MOST SIGNIFICANT

DATA BYTE

LEAST SIGNIFICANT

DATA BYTE

POINTER BYTE

MOST SIGNIFICANT

DATA BYTE

LEAST SIGNIFICANT

DATA BYTE

ACK BY

LM75

ACK BY

MASTER

ACK BY

LM75

ACK BY

LM75

ACK BY

MASTER

ACK BY

LM75

ACK BY

MASTER

START

MASTER

START

MASTER

REPEAT

START

MASTER

START

MASTER

STOP

COND BY

MASTER

STOP

COND BY

MASTER

STOP

COND BY

MASTER

NO ACK BY

MASTER

ACK BY

MASTER

ACK BY

MASTER

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

8 _______________________________________________________________________________________

ADDRESS

BYTE

ADDRESS

BYTE

ADDRESS

BYTE

(a) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FROM CONFIGURATION REGISTER

(b) CONFIGURATION REGISTER WRITE

POINTER

BYTE

POINTER

BYTE

POINTER

BYTE

MOST SIGNIFICANT

DATA BYTE

LEAST SIGNIFICANT

DATA BYTE

CONFIGURATION

BYTE

ADDRESS

BYTE

DATA

BYTE

ACK BY

LM75

ACK BY

LM75

ACK BY

LM75

ACK BY

LM75

ACK BY

LM75

ACK BY

LM75

ACK BY

LM75

START

MASTER

START

MASTER

START

MASTER

REPEAT

START

MASTER

ACK BY

MASTER

STOP

COND BY

MASTER

ACK BY

LM75

ACK BY

LM75

STOP

COND BY

MASTER

STOP

COND BY

MASTER

ACK BY

LM75

Figure 5. I2C-Compatible Timing Diagram (Write)

Temperature Data Format

Temperature data is stored in the Temperature, TOS Set

Point, and THYST Set Point registers. The temperature

data format is 9 bits, two’s complement, and the register

is read out in 2 bytes: an upper byte and a lower byte.

Bits D15–D7 contain the temperature data, with the LSB

representing 0.5°C and the MSB representing the sign

bit (see Table 3). The MSB is transmitted first. The last 7

bits of the lower byte, bits D6–D0, are don’t cares.

Shutdown

Set bit D0 in the Configuration register to 1 to place the

LM75 in shutdown mode and reduce supply current to

4µA. In interrupt mode, entering shutdown resets the

OS output. While in shutdown, the I2C remains active

and TOS and THYST limit registers along with the

Configuration register remain accessible to the master.

Fault Queue

The fault queue prevents OS false tripping in noisy

environments. The number of faults set in the queue (up

to 6) must occur to trip the OS output.

Comparator/Interrupt Mode

The events that trigger OS are identical between com-

parator and interrupt modes. In comparator mode, OS

is asserted when the temperature rises above the TOS

value. OS is deasserted when the temperature drops

below the THYST value. In interrupt mode, OS is assert-

ed when the temperature rises above the TOS value or

falls below the THYST value. OS is deasserted only after

performing a read operation.

OS Output

The OS output is an open-drain output without an inter-

nal pullup. Connect a pullup resistor from OS to +VS.

Using larger resistance values reduces any tempera-

ture errors due to self heating from current entering OS.

OS Polarity

The OS polarity can be programmed for active-low or

active-high operation. In active-low operation, OS goes

low when triggered by a temperature event.

Internal Registers

The LM75’s Pointer register selects between four data

registers (see Figure 6). At power-up, the pointer is set

to read the Temperature register at address 0x00. The

Pointer register latches the last location to which it was

set. All registers are read and write, except the

Temperature register, which is read only.

Write to the Configuration register by writing an address

byte, a data pointer byte, and a data byte. If 2 data

bytes are written, the second data byte overrides the

first. The TOS and THYST registers require 1 address

byte, 1 pointer byte, and 2 data bytes. If only 1 data

byte is written, it is saved in bits D15–D8 of the respec-

tive register. If more than 2 data bytes are written, only

the first 2 bytes are recognized while the remaining

bytes are ignored.

Read from the LM75 in one of two ways. If the location

latched in the Pointer register is set from the previous

read, the new read consists of an address byte, fol-

lowed by retrieving the corresponding number of data

bytes. If the Pointer register needs to be set to a new

address, perform a read operation by writing an

address byte, pointer byte, repeat start, and another

address byte.

An inadvertent 8-bit read from a 16-bit register, with the

D7 bit low, can cause the device to stop in a state

where the SDA line is held low. Ordinarily, this would

prevent any further bus communication until the master

sends nine additional clock cycles or SDA goes high.

At that time, a stop condition resets the device. If the

additional clock cycles are not generated by the mas-

ter, the LM75 bus resets and unlocks after the bus time-

out period has elapsed.

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

_______________________________________________________________________________________ 9

SMBus is a trademark of Intel Corp.

Figure 6. Block Diagram

LM75

+VS

A2/RESET

SDA

SCL OS

SMBus™

INTERFACE

BLOCK

POINTER REGISTER

(SELECTS REGISTER

FOR COMMUNICATION)

DATA ADDRESS

GND

TEMPERATURE

(READ ONLY)

POINTER = 0000 0000

TOS SET POINT

(READ/WRITE)

POINTER = 0000 0011

THYST SET POINT

(READ/WRITE)

POINTER = 0000 0010

CONFIGURATION

(READ/WRITE)

POINTER = 0000 0001

Configuration Register

The 8-bit Configuration register sets the fault queue, OS

polarity, shutdown control, and whether the OS output

functions in comparator or interrupt mode. When writing

to the Configuration register, set bits D7, D6, and D5 to

zero (see Table 5).

Bits D4 and D3, the fault queue bits, determine the

number of faults necessary to trigger an OS condition

(see Table 6). The number of faults set in the queue

must occur consecutively to trip the OS output. The

fault queue prevents OS false tripping in noisy environ-

ments.

Set bit D2, the OS polarity bit, to zero to force the OS

output polarity to active low. Set bit D2 to 1 to set the

OS output polarity to active high. OS is an open-drain

output under all conditions and requires a pullup resis-

tor to output a high voltage (see Figure 1).

Set bit D1, the comparator/interrupt bit to zero to oper-

ate OS in comparator mode. In comparator mode, OS

is asserted when the temperature rises above the TOS

value. OS is deasserted when the temperature drops

below the THYST value (see Figure 1). Set bit D1 to 1 to

operate OS in interrupt mode. OS is asserted in inter-

rupt mode when the temperature rises above the TOS

value or falls below the THYST value. OS is deasserted

only after performing a read operation.

Set bit D0, the shutdown bit, to zero for normal opera-

tion. Set bit D0 to 1 to shutdown the LM75’s internal

blocks. The I2C interface remains active as long as the

shutdown bit is set. The TOS, THYST, and Configuration

registers can still be written to and read from while in

shutdown.

Applications Information

LM75 measures the temperature of its own die. The

thermal path between the die and the outside world

determines the accuracy of temperature measure-

ments. Most of the heat flows in to or out of the die

through the leads. Because of this, the LM75 most easi-

ly measures the PCB temperature. For ambient temper-

ature measurements, mount the LM75 on a separate

PCB away from high power sources. Temperature

errors due to self heating of the LM75 die is minimal

due to the low supply current.

Digital Noise Issues

The lowpass filters in the SCL and SDA digital lines miti-

gate the effects of bus noise, and make communica-

tions in noisy environments more robust. Good layout

practices also help. Keep switching power supplies

away from digital lines, and arrange for high-speed dig-

ital traces to cross SCL and SDA at right angles.

Properly terminate long PCB traces and bus traces

connected to multiple slaves.

Serial bus no-acknowledge (which causes unnecessary

bus traffic) is the most common symptom of excessive

noise coupling into the SDA and SCL lines. Noise with

amplitude greater than the LM75’s hysteresis (400mVP-P,

typ), overshoot greater than 300mV above +VS, and

undershoot more than 300mV below GND may prevent

successful serial communication.

Resistance can be added in series with the SDA and

SCL lines to help filter noise and ringing. A 5kΩresistor

placed in series with the SCL line and as close as pos-

sible to the SCL pin, with the 5pF to 10pF stray capaci-

tance of the device, provides a 6MHz to 12MHz

lowpass filter, which is sufficient filtering in many cases.

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

10 ______________________________________________________________________________________

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 Fault Queue Fault Queue OS Polarity Comparator/

Interrupt Shutdown

Table 5. Configuration Register Definition

D4 D3 NUMBER OF FAULTS

0 0 1 (POR state)

01 2

10 4

11 6

Table 6. Configuration Register Fault

Queue Bits

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

______________________________________________________________________________________ 11

3V to

5.5V

+VS

SCL

SDA

GND

or +V

Microcontroller

SCL

SDA

LM75

10kΩ

GND

Figure 7. I2C Controlled Temperature Sensor

3V to

5.5V

+Vs

LM75

10kΩ

GND

12V

N-CHANNEL MOSFET

12V 300mA

FAN MOTOR

Figure 8. Fan Control

Figure 9. Temperature Sensor with Audible Alarm

3V to

5.5V

+Vs

MAX4364

10kΩ

GND

LM75

0.1μF

6.8nF

200kΩ

SHDN

BIAS

IN+

IN-

OUT-

GND

VCC

OUT+

LM75

Digital Temperature Sensor and Thermal

Watchdog with 2-Wire Interface

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

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

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Package Information

For the latest package outline information and land patterns,

go to www.maxim-ic.com/packages.

Chip Information

PROCESS: CMOS

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

8 SO (SOP) S8-2 21-0041

8 µMAX (µSOP) U8-1 21-0036