DS1775R+T&R - Maxim Integrated Products, Inc.

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FEATURES

§ Temperature measurements require no

external components

§ Measures temperatures from –55°C to

+125°C. Fahrenheit equivalent is –67°F to

257°F

§ Thermometer accuracy is ±2.0°C

§ Thermometer resolution is configurable from

9 to 12 bits (0.5°C to 0.0625°C resolution)

§ Thermostat settings are user definable

§ Data is read from/written to via a 2–wire

serial interface

§ Wide power supply range (2.7V – 5.5V)

§ Software compatible with DS75 2–Wire

Thermal Watchdog in thermometer mode

§ Space–conscious SOT23–5 package with

low thermal time constant

PIN ASSIGNMENT

PIN DESCRIPTION

GND Ground

SCL 2–Wire Serial Clock

SDA 2–Wire Serial Data Input/Output

VDD Power Supply Voltage

O.S. Thermostat Output Signal

DESCRIPTION

The DS1775 SOT23-5 Digital Thermometer and Thermostat provides temperature readings which

indicate the temperature of the device. Thermostat settings and temperature readings are all

communicated to/from the DS1775 over a simple 2–wire serial interface. No additional components are

required; the device is truly a “temperature–to–digital” converter.

For applications that require greater temperature resolution, the user can adjust the readout resolution

from 9 to 12 bits. This is particularly useful in applications where thermal runaway conditions must be

detected quickly.

The open–drain thermal alarm output, O.S., becomes active when the temperature of the device exceeds a

user–defined temperature TOS. The number of consecutive faults required to set O.S. active is

configurable by the user. The device can also be configured in the interrupt or comparator mode, to

customize the method which clears the fault condition.

As a digital thermometer, the DS1775 is software compatible with the DS75 2–Wire Thermal Watchdog.

The DS1775 is assembled in a compact SOT23–5 package allowing for low–cost thermal

monitoring/control in space–constrained applications. The low thermal mass allows for time constants

previously only possible with thermistors.

Applications for the DS1775 include personal computers/servers/workstations, cellular telephones, office

equipment, or any thermally–sensitive system.

DS1775

SOT23-5 Digital Thermomete

and Thermostat

PRODUCT PREVIEW

www.maxim-ic.com

DS1775R

SOT23-5

SDA

VDD

SCL

GND

O.S.

DS1775

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ORDERING INFORMATION

PART ADDR MARKING DESCRIPTION

DS1775R+T&R 000 7750 (See note) DS1775R in Lead-Free 5-Pin SOT-23, 3000 Piece Tape-

and-Reel

DS1775R+U 000 7750 (See note) DS1775R in Lead-Free 5-Pin SOT-23

DS1775R/T&R 000 7750 DS1775R in 5-Pin SOT-23, 3000 Piece Tape-and-Reel

DS1775R-U 000 7750 DS1775R in Lead-Free 5-Pin SOT-23

DS1775R1+T&R 001 7751 (See note) DS1775R1 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R1+U 001 7751 (See note) DS1775R1 in Lead-Free 5-Pin SOT-23

DS1775R1/T&R 001 7751 DS1775R1 in 5-Pin SOT-23, 3000 Piece Tape-and-Reel

DS1775R1-U 001 7751 DS1775R1 in Lead-Free 5-Pin SOT-23

DS1775R2+T&R 010 7752 (See note) DS1775R2 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R2+U 010 7752 (See note) DS1775R2 in Lead-Free 5-Pin SOT-23

DS1775R2/T&R 010 7752 DS1775R2 in 5-Pin SOT-23, 3000 Piece Tape-and-Reel

DS1775R2-U 010 7752 DS1775R2 in Lead-Free 5-Pin SOT-23

DS1775R3+T&R 011 7753 (See note) DS1775R3 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R3+U 011 7753 (See note) DS1775R3 in Lead-Free 5-Pin SOT-23

DS1775R3/T&R 011 7753 DS1775R3 in 5-Pin SOT-23, 3000 Piece Tape-and-Reel

DS1775R3-U 011 7753 DS1775R3 in Lead-Free 5-Pin SOT-23

DS1775R4+T&R 100 7754 (See note) DS1775R4 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R4+U 100 7754 (See note) DS1775R4 in Lead-Free 5-Pin SOT-23

DS1775R4/T&R 100 7754 DS1775R4 in 5-Pin SOT-23, 3000 Piece Tape-and-

Reel

DS1775R4-U 100 7754 DS1775R4 in Lead-Free 5-Pin SOT-23

DS1775R5+T&R 101 7755 (See note) DS1775R5 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R5+U 101 7755 (See note) DS1775R5 in Lead-Free 5-Pin SOT-23

DS1775R5/T&R 101 7755 DS1775R5 in 5-Pin SOT-23, 3000 Piece Tape-and-

Reel

DS1775R5-U 101 7755 DS1775R5 in Lead-Free 5-Pin SOT-23

DS1775R6+T&R 110 7756 (See note) DS1775R6 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R6+U 110 7756 (See note) DS1775R6 in Lead-Free 5-Pin SOT-23

DS1775R6/T&R 110 7756 DS1775R6 in 5-Pin SOT-23, 3000 Piece Tape-and-

Reel

DS1775R6-U 110 7756 DS1775R6 in Lead-Free 5-Pin SOT-23

DS1775R7+T&R 111 7757 (See note) DS1775R7 in Lead-Free 5-Pin SOT-23, 3000 Piece

Tape-and-Reel

DS1775R7+U 111 7757 (See note) DS1775R7 in Lead-Free 5-Pin SOT-23

DS1775R7/T&R 111 7757 DS1775R7 in 5-Pin SOT-23, 3000 Piece Tape-and-

Reel

DS1775R7-U 111 7757 DS1775R7 in Lead-Free 5-Pin SOT-23

Note: A “+” will also be marked on the package.

DS1775

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DETAILED PIN DESCRIPTION Table 1

PIN SYMBOL DESCRIPTION

PIN 1 SCL Clock input/output pin for 2-wire serial communication port. This input

should be tied to GND for standalone thermostat operation.

PIN 2 GND Ground pin.

PIN 3 O.S. Thermostat output Open-drain output becomes active when temperature

exceeds TOS. Device configuration defines means to clear over-temperature

state.

PIN 4 VDD Supply Voltage 2.7V – 5.5V input power pin.

PIN 5 SDA Data input/output pin for 2-wire serial communication port. In the standalone

thermostat mode, this input selects hysteresis.

OVERVIEW

A block diagram of the DS1775 is shown in Figure 1. The DS1775 consists of five major components:

1. Precision temperature sensor

2. Analog–to–digital converter

3. 2–wire interface electronics

4. Data registers

5. Thermostat comparator

The factory–calibrated temperature sensor requires no external components. Upon power–up, the DS1775

begins temperature conversions with the default resolution of 9 bits (0.5°C resolution). The host can

periodically read the value in the temperature register, which contains the last completed conversion. As

conversions are performed in the background, reading the temperature register does not affect the

conversion in progress.

In power–sensitive applications the user can put the DS1775 into a shutdown mode, under which the

sensor will complete and store the conversion in progress and revert to a low–power standby state. In

applications where small incremental temperature changes are critical, the user can change the conversion

resolution from 9 bits to 10, 11, or 12. Each additional bit of resolution approximately doubles the

conversion time. This is accomplished by programming the configuration register. The configuration

thermostat output, number of consecutive faults to trigger an alarm condition, and the method to

terminate an alarm condition.

The user can also program over–temperature (TOS) and under–temperature (THYST) setpoints for

thermostatic operation. The power–up state of TOS is 80°C and that for THYST is 75°C. The result of each

temperature conversion is compared with the TOS and THYST setpoints. The DS1775 offers two modes for

temperature control, the comparator mode and the interrupt mode. This allows the user the flexibility to

customize the condition that would generate and clear a fault condition. Regardless of the mode chosen,

the O.S. output will become active only after the measured temperature exceeds the respective trippoint a

consecutive number of times; the number of consecutive conversions beyond the limit to generate an O.S.

is programmable. The power–up state of the DS1775 is in the comparator mode with a single fault

generating an active O.S.

Digital data is written to/read from the DS1775 via a 2–wire interface, and all communication is MSb

first.

DS1775

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DS1775 FUNCTIONAL BLOCK DIAGRAM Figure 1

OPERATION–Measuring Temperature

The core of DS1775 functionality is its direct–to–digital temperature sensor. The DS1775 measures

temperature through the use of an on–chip temperature measurement technique with an operating range

from –55°C to +125°C. Temperature conversions are initiated upon power–up, and the most recent result

is stored in the thermometer register. Conversions are performed continuously unless the user intervenes

by altering the configuration register to put the DS1775 into a shutdown mode. Regardless of the mode

used, the digital temperature can be retrieved from the temperature register by setting the pointer to that

location (00h, power–up default). The DS1775 power–up default has the sensor automatically performing

9–bit conversions continuously. Details on how to change the settings after power–up are contained in the

“OPERATION–Programming” section.

The resolution of the temperature conversion is configurable (9, 10, 11, or 12 bits), with 9–bit readings

the default state. This equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C.

Following each conversion, thermal data is stored in the thermometer register in two’s complement

format; the information can be retrieved over the 2–wire interface with the device pointer set to the

temperature register. Table 2 describes the exact relationship of output data to measured temperature. The

table assumes the DS1775 is configured for 12–bit resolution; if the device is configured in a lower

resolution mode, those bits will contain zeros. The data is transmitted serially over the 2–wire serial

interface, MSb first. The MSb of the temperature register contains the “sign” (S) bit, denoting whether the

temperature is positive or negative. For Fahrenheit usage, a lookup table or conversion routine must be

used.

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Temperature/Data Relationships Table 2

S 26 2

5 2

4 2

3 2

2 2

1 2

0 MSB

MSb (UNIT = °C) LSb

2-1 2

-2 2

-3 2

-4 0 0 0 0 LSB

TEMP DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT (Hex)

+125°C 0111 1101 0000 0000 7D00h

+25.0625°C 0000 1010 0010 0000 1910h

+10.125°C 0000 1010 0010 0000 0A20h

+0.5°C 0000 0000 1000 0000 0080h

+0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1000 0000 FF80h

-10.125°C 1111 0101 1110 0000 F5E0h

-25.0625°C 1110 0110 1111 0000 E6F0h

-55°C 1100 1001 0000 0000 C900h

OPERATION–Thermostat Control

In its comparator operating mode, the DS1775 functions as a thermostat with programmable hysteresis, as

shown in Figure 2. When the DS1775’s temperature meets or exceeds the value stored in the high

temperature trip register (TOS) a consecutive number of times, as defined by the configuration register, the

output becomes active and stays active until the first time that the temperature falls below the temperature

stored in the low temperature trigger register (THYST). In this way, any amount of hysteresis may be

obtained. The DS1775 powers up in the comparator mode with TOS=80°C and THYST=75°C and can be

used as a standalone thermostat (no 2–wire interface required) with those setpoints.

In the interrupt mode, the O.S. output will first become active following the programmed number of

consecutive conversions above TOS. The fault can only be cleared by either setting the DS1775 in a

shutdown mode or by reading any register (temperature, configuration, TOS, or THYST) on the device.

Following a clear, a subsequent fault can only occur if consecutive conversions fall below THYST. This

interrupt/clear process is thus cyclical (TOS, clear, THYST, clear, TOS, clear, THYST, clear, ...). Only the first

of multiple consecutive TOS violations will activate O.S., even if each fault is separated by a clearing

function. The same situation applies to multiple consecutive THYST events.

DS1775

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O.S. OUTPUT TRANSFER FUNCTION Figure 2

Regardless of the mode chosen, the O.S. output is open–drain and the active state is set in the

configuration register. The power–up default is active low. Refer to the “OPERATION–Programming”

section for instructions in adjusting the thermostat setpoints, thermostat mode, and O.S. active state.

OPERATION–Programming

There are three areas of interest in programming the DS1775: the configuration register, the TOS register,

and the THYST register. All programming is done via the 2–wire interface by setting the pointer to the

appropriate location. Table 3 illustrates the pointer settings for the four registers of the DS1775.

Pointer Register Structure Table 3

POINTER ACTIVE REGISTER

00h Temperature (default)

01h Configuration

02h THYST

03h TOS

The DS1775 will power up with the temperature register selected. If the host wishes to change the data

pointer it simply addresses the DS1775 in the write mode (R/ W=0), receives an acknowledge, and writes

the 8 bits that correspond to the new desired location. The last pointer location is always maintained so

that consecutive reads from the same register do not require the host to always provide a pointer address.

The only exception is at power–up, in which case the pointer will always be set to 00h, the temperature

DS1775

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address is currently selected. Please refer to the “2–Wire Serial Data Bus” section for details of the 2–

wire bus protocol.

Configuration Register Programming

The configuration register is accessed if the DS1775 pointer is currently set to the 01h location. Writing

to or reading from the register is determined by the R/W bit of the 2–wire control byte (See “2–wire

Serial Data Bus” section). Data is read from or written to the configuration register MSb first. The format

of the register is illustrated below in Figure 3. The effect each bit has on DS1775 functionality is

described below along with the power–up state of the bit. The user has read/write access to all bits in the

configuration register. The entire register is volatile, and thus it will power–up in the default state.

Configuration/Status Register Figure 3

0 R1 R0 F1 F0 POL TM SD

MSb LSb

SD = Shutdown bit. If SD is “0”, the DS1775 will continuously perform temperature conversions and

store the last completed result in the thermometer register. If SD is changed to “1”, the conversion in

progress will be completed and stored; then the device will revert to a low–power standby mode. The

O.S. output will be cleared if the device is in the interrupt mode and remain unchanged in the comparator

mode. The 2–wire port remains active. The power–up default state is “0” (continuous conversion mode).

TM = Thermostat mode. If TM=“0”, the DS1775 is in the comparator mode. TM=“1” sets the device to

the interrupt mode. See “OPERATION–Thermostat Control” section for a description of the difference

between the two modes. The power–up default state of the TM bit is “0” (comparator mode).

POL = O.S. Polarity Bit. If POL = “1”, the active state of the O.S. output will be high. A “0” stored in

this location sets the thermostat output to an active low state. The user has read/write access to the POL

bit, and the power–up default state is “0” (active low).

F0, F1 = O.S. Fault Tolerance bits. The fault tolerance defines the number of consecutive conversions

returning a temperature beyond limits is required to set the O.S. output in an active state. This may be

necessary to add margin in noisy environments. Table 4 below defines the four settings. The DS1775 will

power up with F0=F1=“0”, such that a single occurrence will trigger a fault.

Fault Tolerance Configuration Table 4

F1 F0 Consecutive conversions beyond limits to generate fault

0 0 1

0 1 2

1 0 4

1 1 6

R0, R1 = Thermometer resolution bits. Table 5 defines the resolution of the digital thermometer, based

on the settings of these two bits. There is a direct trade-off between resolution and conversion time, as

depicted in the AC Electrical Characteristics. The default state is R0="0" and R1="0" (9–bit conversions).

DS1775

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Thermometer Resolution Configuration Table 5

R1 R0 Thermometer Resolution Max Conversion Time

0 0 9-bit 0.1875s

0 1 10-bit 0.375s

1 0 11-bit 0.75s

1 1 12-bit 1.5s

Thermostat Setpoints Programming

The thermostat registers (TOS and THYST) can be programmed or read via the 2–wire interface. TOS is

accessed by setting the DS1775 data pointer to the 03h location, and to the 02h location for THYST.

The format of the TOS and THYST registers is identical to that of the Thermometer register; that is, 12–bit

2’s complement representation of the temperature in °C. The user can program the number of bits (9, 10,

11, or 12) for each TOS and THYST that corresponds to the thermometer resolution mode chosen. For

example, if the 9–bit mode is chosen the 3 least significant bits of TOS and THYST will be ignored by the

thermostat comparator. The format for both TOS and THYST is shown in Table 6. The power–up default

for TOS is 80°C and for THYST is 75°C.

Thermostat Setpoint (TOS/THYST) Format Table 6

S 26 2

5 2

4 2

3 2

2 2

1 2

0 MSB

MSb (UNIT = °C) LSb

2-1 2

-2 2

-3 2

-4 0 0 0 0 LSB

TEMPERATURE/DATA RELATIONSHIPS

TEMP DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT (Hex)

+80°C 0101 0000 0000 0000 5000h

+75°C 0100 1011 0000 0000 4B00h

+10.125°C 0000 1010 0010 0000 0A20h

+0.5°C 0000 0000 1000 0000 0080h

+0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1000 0000 FF80h

-10.125°C 1111 0101 1110 0000 F5E0h

-25.0625°C 1110 0110 1111 0000 E6F0h

-55°C 1100 1001 0000 0000 C900h

If the user does not wish to take advantage of the thermostat capabilities of the DS1775, the 24 bits can be

used for general storage of system data that need not be maintained following a power loss.

DS1775

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2–WIRE SERIAL DATA BUS

The DS1775 supports a bi–directional 2-wire bus and data transmission protocol. A device that sends data

onto the bus is defined as a transmitter, and a device receiving data as a receiver. The device that controls

the message is called a “master”. The devices that are controlled by the master are “slaves”. The bus must

be controlled by a master device which generates the serial clock (SCL), controls the bus access, and

generates the START and STOP conditions. The DS1775 operates as a slave on the two–wire bus.

Connections to the bus are made via the open–drain I/O lines SDA and SCL.

The following bus protocol has been defined (See Figure 4):

· Data transfer may be initiated only when the bus is not busy.

· During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in

the data line while the clock line is high will be interpreted as control signals.

Accordingly, the following bus conditions have been defined:

Bus not busy: Both data and clock lines remain HIGH.

Start data transfer: A change in the state of the data line, from HIGH to LOW, while the clock is HIGH,

defines a START condition.

Stop data transfer: A change in the state of the data line, from LOW to HIGH, while the clock line is

HIGH, defines the STOP condition.

Data valid: The state of the data line represents valid data when, after a START condition, the data line

is stable for the duration of the HIGH period of the clock signal. The data on the line must be changed

during the LOW period of the clock signal. There is one clock pulse per bit of data.

Each data transfer is initiated with a START condition and terminated with a STOP condition. The

number of data bytes transferred between START and STOP conditions is not limited, and is determined

by the master device. The information is transferred byte–wise and each receiver acknowledges with a

ninth bit.

Within the bus specifications a regular mode (100kHz clock rate) and a fast mode (400kHz clock rate) are

defined. The DS1775 works in both modes.

Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the

reception of each byte. The master device must generate an extra clock pulse which is associated with this

acknowledge bit.

A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a

way that the SDA line is stable LOW during the HIGH period of the acknowledge related clock pulse. Of

course, setup and hold times must be taken into account. A master must signal an end of data to the slave

by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this case,

the slave must leave the data line HIGH to enable the master to generate the STOP condition.

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DATA TRANSFER ON 2–WIRE SERIAL BUS Figure 4

Figure 5 details how data transfer is accomplished on the two–wire bus. Depending upon the state of the

R/W bit, two types of data transfer are possible:

1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the

master is the slave address. Next follows a number of data bytes. The slave returns an acknowledge

bit after each received byte.

2. Data transfer from a slave transmitter to a master receiver. The first byte (the slave address) is

transmitted by the master. The slave then returns an acknowledge bit. Next follows a number of data

bytes transmitted by the slave to the master. The master returns an acknowledge bit after all received

bytes other than the last byte. At the end of the last received byte, a ‘not acknowledge’ is returned.

The master device generates all of the serial clock pulses and the START and STOP conditions. A

transfer is ended with a STOP condition or with a repeated START condition. Since a repeated START

condition is also the beginning of the next serial transfer, the bus will not be released.

The DS1775 may operate in the following two modes:

1. Slave receiver mode: Serial data and clock are received through SDA and SCL. After each byte is

received, an acknowledge bit is transmitted. START and STOP conditions are recognized as the

beginning and end of a serial transfer. Address recognition is performed by hardware after reception

of the slave address and direction bit.

2. Slave transmitter mode: The first byte is received and handled as in the slave receiver mode.

However, in this mode, the direction bit will indicate that the transfer direction is reversed. Serial data

is transmitted on SDA by the DS1775 while the serial clock is input on SCL. START and STOP

conditions are recognized as the beginning and end of a serial transfer.

SLAVE ADDRESS

A control byte is the first byte received following the START condition from the master device. The

control byte consists of a four bit control code; for the DS1775, this is set as 1001 binary for read and

write operations. The next three bits of the control byte are the device select bits (A2, A1, A0). These bits

are set to 000 (A2="0", A1="0", A0="0") for the DS1775R/TRL and vary according to the device's part

number as specified in the "Ordering Information" section. They are used by the master device to select

which of eight devices are to be accessed. The set bits are in effect the three least significant bits of the

slave address. The last bit of the control byte (R/ W) defines the operation to be performed. When set to a

"1" a read operation is selected, and when set to a "0" a write operation is selected. Following the START

condition, the DS1775 monitors the SDA bus checking the device type identifier being transmitted. Upon

receiving the 1001 code and appropriate device select bits of 000, the DS1775 outputs an acknowledge

signal on the SDA line.

DS1775

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2–WIRE SERIAL COMMUNICATION WITH DS1775 Figure 5

DS1775

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ABSOLUTE MAXIMUM RATINGS*

Voltage on VDD, Relative to Ground –0.3V to +7.0V

Voltage on any other pin, Relative to Ground –0.3V to +7.0V

Operating Temperature –55°C to +125°C

Storage Temperature –55°C to +125°C

Soldering Temperature See J-STD-020A Specification

* This is a stress rating only and functional operation of the device at these or any other conditions above

those indicated in the operation sections of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods of time may affect reliability.

DC ELECTRICAL CHARACTERISTICS

(–55°C to +125°C; 2.7V £ VDD £ 5.5V)

PARAMETER

SYMBOL

CONDITION MIN

TYP

MAX UNITS NOTES

Supply Voltage VDD 2.7 5.5 V 1

Input Logic High VIH 0.7 VDD V

DD+0.5 V 1

Input Logic Low VIL -0.5 0.3VDD V 1

VOL1 3 mA sink

current

0 0.4 SDA Output Logic Low

Voltage

VOL2 6 mA sink

current

0 0.6

V 1

O.S. Saturation Voltage VOL 4 mA sink

current

0.8 V 1,9

Input current each I/O pin 0.4 < VI/O <

0.9VDD

-10 +10 mA 2

I/O Capacitance CI/O 10 pF

Standby Current IDD1 1

mA 3,4

Active Temp.

Conversions

1000 Active Current IDD

Communication

only

100

mA 3,4

ELECTRICAL CHARACTERISTICS:

DIGITAL THERMOMETER (–55°C to +125°C; 2.7V £ VDD £ 5.5V)

PARAMETER

SYMBOL

CONDITION MIN

TYP

MAX UNITS NOTES

Thermometer Error TERR

–10

C to +85

–55

C to 125

±2.0

±3.0

9, 10

Resolution 9 12 bits

9-bit

conversion

125 187.5

10-bit

conversion

250 375

11-bit

conversion

500 750

Conversion Time tCONVT

12-bit

conversion

1000 1500

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AC ELECTRICAL CHARACTERISTICS:

2–WIRE INTERFACE (–55°C to +125°C; VDD =2.7V to 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

SCL clock frequency fSCL Fast Mode

Standard Mode

400

100

KHZ

Bus free time between a

STOP and START

condition

tBUF Fast Mode

Standard Mode

1.3

4.7

Hold time (repeated)

START condition

tHD:STA Fast Mode

Standard Mode

0.6

4.0

ms 5

LOW period of SCL tLOW Fast Mode

Standard Mode

1.3

4.7

HIGH period of SCL tHIGH Fast Mode

Standard Mode

0.6

4.0

Set-up time for a

repeated START

tSU:STA Fast Mode

Standard Mode

0.6

4.7

Data hold time tHD:DAT Fast Mode

Standard Mode

0.9

ms 6

Data set-up time tSU:DAT Fast Mode

Standard Mode

100

250

ns 7

Rise time of both SDA and

SCL signals

tR Fast Mode

Standard Mode

20+

0.1CB

300

1000

ns 8

Fall time of both SDA and

SCL signals

tF Fast Mode

Standard Mode

20+

0.1CB

300

ns 8

Set-up time for STOP tSU:STO Fast Mode

Standard Mode

0.6

4.0

Capacitive load for each bus

line

Cb 400 pF 8

Input Capacitance CI 5 pF

NOTES:

1. All voltages are referenced to ground.

2. I/O pins of fast mode devices must not obstruct the SDA and SCL lines if VDD is switched off.

3. IDD specified with O.S. pin open.

4. IDD specified with VDD at 5.0V and SDA, SCL = 5.0V, 0°C to +70°C.

5. After this period, the first clock pulse is generated.

6. The maximum tHD:DAT has only to be met if the device does not stretch the LOW period (tLOW ) of the

SCL signal.

7. A fast mode device can be used in a standard mode system, but the requirement tSU:DAT ³ 250 ns must

then be met. This will automatically be the case if the device does not stretch the LOW period of the

SCL signal. If such a device does stretch the LOW period of the SCL signal, it must output the next

data bit to the SDA line tR MAX +tSU:DAT = 1000+250 = 1250 ns before the SCL line is released.

8. Cb – total capacitance of one bus line in pF.

9. Internal heating caused by O.S. loading will cause the DS1775 to read approximately 0.5ºC higher if

O.S. is sinking the max rated current.

10. Contact the factory in Dallas, (972) 371-4448, for operation requiring temperature readings greater

than 120°C.

DS1775

14 of 14

TIMING DIAGRAMS Figure 6