DS1722
Digital Thermometer with
SPI/3-Wire Interface
www.maxim-ic.com
FEATURES
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 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 SO (150mil) and 8-Pin
μMAX
package
V
DDD
CE
SCLK
GND
PIN ASSIGNMENT
1
2
3
4
8
7
6
5
V
DDA
SERMODE
SDI
SDO
V
DDD
CE
SCLK
GND
1*
2
3
4
8
7
6
5
V
DDA
SERMODE
SDI
SDO
DS1722S
8-Pin SO (150mil)
DS1722U
8-PIN µMAX
PIN DESCRIPTION
SERMODE
CE
SCLK
GND
V
DDA
SDO
SDI
V
DDD
- Serial Interface Mode
- Chip Enable
- Serial Clock
- Ground
- Analog Supply Voltage
- Serial Data Out
- Serial Data In
- 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 standard 3-wire serial interface. The choice of interface standard 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 SO (150mil) and 8-pin
μMAX
package.
Applications for the DS1722 include personal computers/servers/workstations, cellular telephones, office
equipment, or any thermally-sensitive system.
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022008
DS1722
ORDERING INFORMATION
Table 1
PART
DS1722S
DS1722S/T&R
DS1722S+
DS1722S+T&R
DS1722U
DS1722U/T&R
DS1722U+
MARKING
DS1722
DS1722
DS1722
(See note)
DS1722
(See note)
1722
1722
DESCRIPTION
DS1722 in 150mil 8-Pin SO
DS1722 in 150mil 8-Pin SO, 2500 Piece Tape-and-
Reel
DS1722 in Lead-Free 150mil 8-Pin SO
DS1722 in Lead-Free 150mil 8-Pin SO, 2500 Piece
Tape-and-Reel
DS1722 in 8-Pin µMAX
DS1722 in 8-Pin µMAX, 3000 Piece Tape-and-
Reel
DS1722 in Lead-Free 8-Pin µMAX
1722
(See note)
DS1722U+T&R
1722
DS1722 in Lead-Free 8-Pin µMAX, 3000 Piece
(See note)
Tape-and-Reel
Note: A “+” will also be marked on the package next to the pin 1 indicator.
DETAILED PIN DESCRIPTION
Table 2
SOIC
PIN 1
PIN 2
PIN 3
PIN 4
PIN 5
SYMBOL
V
DDD
CE
SCLK
GND
SDO
DESCRIPTION
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 V
CC
; standard 3-wire when connected to
GND.
Analog Supply Voltage
2.65V – 5.5V input power pin.
PIN 6
SDI
PIN 7
PIN 8
SERMODE
V
DDA
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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 power-
conserving shutdown state upon power-up. After power-up, the user may alter the configuration 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.
The DS1722 can communicate using either a Motorola Serial Peripheral Interface (SPI) or standard 3-
wire interface. The user can select either communication standard through the SERMODE pin, tying it to
V
DDD
for SPI and to ground for 3-wire.
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.
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DS1722 FUNCTIONAL BLOCK DIAGRAM
Figure 1
DS1722
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 measurement technique with an operating range
from -55° to +120°C. The device powers up in a power-conserving shutdown mode. After power-up, the
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 power-
up are contained in the “OPERATION-Programming” section.
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 3 describes the exact 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.
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Temperature/Data Relationships
Table 3
2
6
2
5
2
4
2
3
(unit =
°C)
2
-2
2
-3
2
-4
0
0
0
2
2
2
1
2
0
LSb
0
DS1722
Address
Location
S
MSb
2
-1
02h
01h
TEMPERATURE
+120°C
+25.0625°C
+10.125°C
+0.5°C
0°C
-0.5°C
-10.125°C
-25.0625°C
-55°C
DIGITAL OUTPUT
(BINARY)
0111 1000 0000 0000
0001 1001 0001 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
DIGITAL OUTPUT
(HEX)
7800h
1910h
0A20h
0080h
0000h
FF80h
F5E0h
E6F0h
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 by selecting the appropriate address of the desired register
location. Table 4 illustrates the addresses for the two registers (configuration and temperature) of the
DS1722.
Register Address Structure
Table 4
Read Address
00h
01h
02h
Write Address
80h
No access
No access
Active Register
Configuration
Temperature LSB
Temperature MSB
CONFIGURATION REGISTER PROGRAMMING
The configuration register is accessed in the DS1722 with the 00h address for reads and the 80h address
for writes. Data is read from or written to the configuration register MSb first for SPI communication and
LSb first for 3-wire communication. The format of the register is illustrated in Figure 2. The effect each
bit has on DS1722 functionality is described below along with the power-up state of the bit. The entire
register is volatile, and thus it will power-up in the default state.
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