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19-6687; Rev 5/13

GENERAL DESCRIPTION

The DS1775 digital thermometer and thermostat

provides temperature readings that indicate the

device’s temperature. 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 T

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 5-pin SOT23 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

• Personal Computers/Servers/Workstations

• Cell Phones

• Office Equipment

• Any Thermally-Sensitive System

FEATURES

• Temperature Measurements Require No

External Components

• Measures Temperatures from -55°C to

+125°C (-67°F to +257°F)

• ±2.0°C Thermometer Accuracy

• Thermometer Resolution is Configurable

from 9 Bits to 12 Bits (0.5°C to 0.0625°C

Resolution)

• User-Definable Thermostat Settings

• Data is Read From/Written to Through a

2-Wire Serial Interface

• 2.7V to 5.5V Wide Power-Supply Range

• Software Compatible with DS75 2-Wire

Thermal Watchdog in Thermometer Mode

• Space-Conscious 5-Pin SOT23 Package with

Low Thermal Time Constant

PIN CONFIGURATION

PIN DESCRIPTION

GND Ground

SCL 2-Wire Serial Clock

SDA 2-Wire Serial Data Input/Output

Power-Supply Voltage

O.S. Thermostat Output Signal

Ordering Information appears at end of data sheet.

DS1775

Digital Thermometer

and Thermostat in SOT23

SOT23

SDA

SCL

GND

O.S.

Summary of content (14 pages)

PAGE 1
DS1775 Digital Thermometer and Thermostat in SOT23 GENERAL DESCRIPTION FEATURES • The DS1775 digital thermometer and thermostat provides temperature readings that indicate the device’s temperature. 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-todigital” converter.
PAGE 2
DS1775 Table 1. Detailed Pin Description PIN NAME FUNCTION Clock Input/Output for 2-Wire Serial Communication Port. This input should 1 SCL be tied to GND for stand-alone thermostat operation. 2 GND Ground Thermostat Output. Open-drain output becomes active when temperature 3 O.S. exceeds TOS. Device configuration defines means to clear overtemperature state. 4 VDD Supply Voltage 2.7V to 5.5V Input Power Pin Data Input/Output for 2-Wire Serial Communication Port.
PAGE 3
DS1775 Figure 1. Block Diagram 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.
PAGE 4
DS1775 Table 2. Temperature/Data Relationships S 26 25 MSb 2-1 24 23 22 21 2-3 TEMPERATURE (°C) +125 +25.0625 +10.125 +0.5 0 -0.5 -10.125 -25.
PAGE 5
DS1775 Figure 2. O.S. Output Transfer Function 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. See the Programming section for instructions in adjusting the thermostat setpoints, thermostat mode, and O.S. active state. Programming There are three areas of interest in programming the DS1775: the configuration register, the TOS register, and the THYST register.
PAGE 6
DS1775 temperature register. The pointer address must always precede data in writing to a register, regardless of which address is currently selected. See 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 the 2-Wire Serial Data Bus section).
PAGE 7
DS1775 R0, R1 = Thermometer resolution bits. Table 6 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 shown in the AC Electrical Characteristics. The default state is R0 = 0 and R1 = 0 (9-bit conversions). Table 6. Thermometer Resolution Configuration THERMOMETER RESOLUTION R1 R0 (BITS) 0 0 9 0 1 10 1 0 11 1 1 12 MAX CONVERSION TIME (SECONDS) 0.1875 0.375 0.75 1.
PAGE 8
DS1775 2-WIRE SERIAL DATA BUS The DS1775 supports a bidirectional 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.
PAGE 9
DS1775 Figure 3. Data Transfer on 2-Wire Serial Bus Figure 3 details how data transfer is accomplished on the 2-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.
PAGE 10
DS1775 Figure 4.
PAGE 11
DS1775 ABSOLUTE MAXIMUM RATINGS (Voltages relative to ground.) Voltage Range on VDD Voltage Range on Any Other Pin Operating Temperature Range Storage Temperature Range Lead Temperature (soldering, 10s) Soldering Temperature (reflow) -0.3V to +7.0V -0.3V to +7.0V -55°C to +125°C -55°C to +125°C +300°C +260°C 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.
PAGE 12
DS1775 AC ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (VDD = 2.7V to 5.5V, TA = -55°C to +125°C, unless otherwise noted.) (Figure 5) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS NOTES Fast mode 400 SCL Clock Frequency fSCL kHz Standard mode 100 Bus Free Time Fast mode 1.3 Between a STOP and tBUF µs Standard mode 4.7 START Condition Fast mode 0.6 Hold Time (Repeated) tHD:STA 5 µs START Condition Standard mode 4.0 Fast mode 1.3 Low Period of SCL tLOW µs Standard mode 4.7 Fast mode 0.
PAGE 13
DS1775 Figure 5.
PAGE 14
DS1775 REVISION HISTORY REVISION DATE 5/13 DESCRIPTION Updated the Absolute Maximum Ratings, Ordering Information, Package Information sections PAGES CHANGED 12, 13 14 of 14 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 specifications without notice at any time.