Rainbow Electronics DS1722 User Manual

www.dalsemi.com

PRELIMINARY

DS1722

Digital Thermometer with

SPI/3-Wire Interface

FEATURES

PIN ASSIGNMENT

 Temperature measurements require no

external components

 Measures temperatures from -55°C to

+120°C. Fahrenheit equivalent is -67°F to +248°F

 Thermometer accuracy is ±2.0°C  Thermometer resolution is configurable from

DDD

SCLK

GND

1 2 3 4

DS1722S

8-Pin SOIC (150-mil)

V 7 6

SDI

SDO

V CE SCLK

GND

DDD

1 8 2 7 3 6

4 5

DS1722U

8-PIN

-SOP

DDA

SERMODE SDI

SDO

8 to 12 bits (1.0°C to 0.0625°C resolution)

 Data is read from/written to via a Motorola

Serial Peripheral Interface (SPI) or standard 3-wire serial interface

 Wide analog power supply range (2.65V -

5.5V)

 Separate digital supply allows for 1.8V logic  Available in an 8-pin SOIC (150 mil), 8-pin

uSOP, and flip chip package

PIN DESCRIPTION

SERMODE - Serial Interface Mode CE - Chip Enable SCLK - Serial Clock GND - Ground V

DDA

SDO - Serial Data Out SDI - Serial Data In V

DDD

- Analog Supply Voltage

- Digital Supply Voltage

DESCRIPTION

The DS1722 Digital Thermometer and Thermostat with SPI/3-Wire Interface provides temperature readings which indicate the temperature of the device. No additional components are required; the device is truly a temperature-to-digital converter. Temperature readings are communicated from the DS1722 over a Motorola SPI interface or a stand ard 3-wire serial interface. Th e choice of interface standa rd is selectable by the user.

For applications that require greater temperature resolution, the user can adjust the readout resolution from 8 to 12 bits. This is particularly useful in applications where thermal runaway conditions must be detected quickly.

For application flexibility, the DS1722 features a wide analog supply rail of 2.65V - 5.5V. A separate digital supply allows a range of 1.8V to 5.5V.

The DS1722 is available in an 8-pin SOIC (150-mil), 8-pin uSOP, and flip chip package.

Applications for the DS1722 include personal computers/servers/workstations, cellular telephones, office equipment, or any thermally-sensitive system.

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DETAILED PIN DESCRIPTION Table 1

SOIC SYMBOL DESCRIPTION PIN 1

PIN 2

PIN 3 PIN 4

PIN 5

PIN 6

PIN 7

PIN 8

DDD

SCLK

GND

SDO

SDI

SERMODE

DDA

Digital Supply Voltage 1.8V-5.5V. Defines the top rails for the digital inputs and outputs. Chip Enable Must be asserted high for communication to take place for either the SPI or 3-wire interface. Serial Clock Input Used to synchronize data movement on the serial interface for either the SPI or 3-wire interface.

Ground pin. Serial Data Output When SPI communication is selected, the SDO pin is

the serial data output for the SPI bus. When 3-wire communication is selected, this pin must be tied to the SDI pin (the SDI and SDO pins function as a single I/O pin when tied together.) Serial Data Input When SPI communication is selected, the SDI pin is the serial data input for the SPI bus. When 3-wire communication is selected, this pin must be tied to the SDO pin (the SDI and SDO pins function as a single I/O pin when tied together.) Serial Interface Mode Input This pin selects which interface standard will be used: SPI when connected to VCC ; standard 3-wire when connected to GND.

Analog Supply Voltage 2.65V – 5.5V input power pin.

DS1722

OVERVIEW

A block diagram of the DS1722 is shown in Figure 1. The DS1722 consists of four major components:

1. Precision temperature sensor

2. Analog-to-digital converter

3. SPI/3-wire interface electronics

4. Data registers

The factory-calibrated temperature sensor requires no external components. The DS1722 is in a powerconserving shutdown state upon power-up. After power-up, the user ma y alter the confi guration register to place the device in a continuous temperature conversion mode or in a one-shot conversion mode. In the continuous conversion mode, the DS1722 continuously converts the temperature and stores the result in the temperature register. As conversions are performed in the background, reading the temperature register does not affect the conversion in progress. In the one-shot temperature conversion mode, the DS1722 will perform one temperature conversion, store the result in the temperature register, and then return to the shutdown state. This conversion mode is ideal for power sensitive applications. More information on the configuration register is contained in the “OPERATION-Programming” section.

The temperature conversion results will have a default resolution of 9 bits. In applications where small incremental temperature changes are critical, the user can change the conversion resolution from 9 bits to 8, 10, 11, or 12. This is accomplished by programming the configuration register. Each additional bit of resolution approximately doubles the conversion time.

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DS1722

The DS1722 can communicate using either a Motorola Serial Peripheral Interface (SPI) or standard 3wire interface. The user can select ei the r comm unicat ion standa rd t hrou gh the SER MODE pin, tying it to V

for SPI and to ground for 3-wire.

DDD

The device contains both an analog supply voltage and a digital supply voltage (V

DDA

and V

DDD

respectively). The analog supply powers the device for operation while the digital supply provides the top rails for the digital inputs and outputs. The DS1722 was designed to be 1.8V Logic-Ready.

DS1722 FUNCTIONAL BLOCK DIAGRAM Figure 1

OPERATION-Measuring Temperature

The core of DS1722 functionality is its direct-to-digital temperature sensor. The DS1722 measures temperature through the use of an on-chip temperature measurem ent technique with an operating range from -55°=to +120°C. The device powers up in a power-conserving shutdown mode. After power-up, th e DS1722 may be placed in a continuous conversion mode or in a one-shot conversion mode. In the continuous conversion mode, the device continuously computes the temperature and stores the most recent result in the temperature register at addresses 01h (LSB) and 02h (MSB). In the one-shot conversion mode, the DS1722 performs one temperature conversion and then returns to the shutdown mode, storing temperature in the temperature register. Details on how to change the setting after powerup are contained in the “OPERATION-Programming” section.

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DS1722

The resolution of the temperature conversion is configurable (8, 9, 10, 11, or 12 bits), with 9-bit readings the default state. This equates to a temperature resolution of 1.0°C, 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 SPI or 3-wire interface with the address set to the temperature register, 01h (LSB) and then 02h (MSB). Table 2 describes the ex act relationship of output data to measured temperature. The table assumes the DS1722 is configured for 12-bit resolution; if the device is configured in a lower resolution mode, those bits will contain 0s. The data is transmitted serially over the digital interface, MSb first for SPI communication and LSb first for 3-wire communication. 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.

Temperature/Data Relationships Table 2

Address Location

S262

MSb (unit = °C) LSb

02h

-1

TEMPERATURE

-2

+120°C

+25.0625°C

+10.125°C

+0.5°C

0°C

-0.5°C

-10.125°C

-25.0625°C

-55°C

-3

-4

000001h

DIGITAL OUTPUT

(BINARY)

DIGITAL OUTPUT

(HEX)

0111 1000 0000 0000 7800h 0001 1001 0001 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-Programming

The area of interest in programming the DS1722 is the Configuration register. All programming is done via the SPI or 3-wire communication interface b y selecting the approp riate add ress of the desired register location. Table 3 illustrates the addresses for the two registers (configuration and temperature) of the DS1722.

Read Address Write Address Active Register

00h 80h Configuration 01h No access Temperature LSB 02h No access Temperature MSB

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