dallas semiconductor DS1775 service manual

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DS1775

SOT23-5 Digital Thermomete

www.maxim-ic.com

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

PIN ASSIGNMENT

SCL

GND

O.S.

DS1775R

SOT23-5

PIN DESCRIPTION

GND Ground
SCL 2–Wire Serial Clock
SDA 2–Wire Serial Data Input/Output
V

Power Supply Voltage

DD

O.S. Thermostat Output Signal

and Thermostat

1

2

3

SDA

5

V

4

DD

low thermal time constant

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.

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DS1775

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.

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DS1775

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 T

. Device configuration defines means to clear over-temperature

OS

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
register defines the conversion state, thermometer resolution/conversion time, active state of the
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 (T
thermostatic operation. The power–up state of T

temperature conversion is compared with the T

is 80°C and that for T

OS

and T

OS

setpoints. The DS1775 offers two modes for

HYST

is 75°C. The result of each

HYST

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.

) setpoints for

HYST

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DS1775 FUNCTIONAL BLOCK DIAGRAM Figure 1

DS1775

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

DS1775

0

MSB

MSb

2-1 2

-2

2

-3

2

(UNIT = °C)

-4

0 0 0 0 LSB

LSb

TEMP DIGITAL OUTPUT

DIGITAL OUTPUT (Hex)

(Binary)

+125°C

+25.0625°C

+10.125°C

+0.5°C

+0°C

-0.5°C

-10.125°C

-25.0625°C

-55°C

0111 1101 0000 0000 7D00h
0000 1010 0010 0000 1910h
0000 1010 0010 0000 0A20h
0000 0000 1000 0000 0080h
0000 0000 0000 0000 0000h
1111 1111 1000 0000 FF80h
1111 0101 1110 0000 F5E0h
1110 0110 1111 0000 E6F0h
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 (T
obtained. The DS1775 powers up in the comparator mode with TOS=80°C and T
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 T
Following a clear, a subsequent fault can only occur if consecutive conversions fall below T
interrupt/clear process is thus cyclical (T
of multiple consecutive T

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

OS

, clear, T

OS

function. The same situation applies to multiple consecutive T

). In this way, any amount of hysteresis may be

HYST

=75°C and can be

HYST

) on the device.

HYST

HYST

, clear, TOS, clear, T

HYST

HYST

events.

, clear, ...). Only the first

HYST

. This

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