Rainbow Electronics DS1721 User Manual

Download

www.dalsemi.com

DS1721

2-Wire Digital Thermomete

and Thermostat

FEATURES

 Temperature measurements require no

external components with ±1°C accuracy

 Measures temperatures from -55°C to

+125°C; Fahrenheit equivalent is -67°F to +257°F

 Temperature resolution is configurable from 9

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

 Maximum conversion time (9-bit resolution)

of 150 ms

 Thermostatic settings are user-definable  Data is read/written via a 2-wire serial

interface (open drain I/O lines); 3-bit addressability

 Wide power supply range (2.7V - 5.5V)  Applications include personal computers,

cellular telephones, office equipment, or any thermally sensitive system

 8-pin, 150-mil SOIC package and 8-pin µSOP

package

PIN ASSIGNMENT

SDA

SCL

OUT

GND

1 8 2 7

DS1721S

8-Pin SOIC (150-mil)

SDA

SCL

OUT

GND

DS1721U

8-PIN µ-SOP

V A A

PIN DESCRIPTION

SDA - 2-Wire Serial Data Input/Output SCL - 2-Wire Serial Clock GND - Ground T A A A V

OUT

0 1 2 DD

- Thermostat Output Signal

- Chip Address Input

- Power Supply Voltage (+5V)

DD 0 1

DESCRIPTION

The DS1721 2-Wire Digital Thermometer and Thermostat provides 12-bit temperature readings which indicate the temperature of the device. Thermostatic settings and temperature readings are all communicated to/from the DS1721 over a simple 2-wire serial interface. No additional components are required; the device is truly a “temperature-to-digital” converter.

The DS1721 has three address bits that allow a user to multidrop up to eight sensors along the 2-wire bus, greatly simplifying the bussing of distributed temperature sensing networks.

The thermal alarm output, T temperature TH. The output remains active until the temperature is equal to or below the user-defined temperature TL, allowing for any hysteresis necessary. The active state of T user.

For applications that require faster conversion times, the user can adjust the readout resolution from 12 to 9 bits, effectively reducing the conversion time from 1.2 s (MAX) to 150 ms (MAX). This is particularl y useful in applications where temperature changes large magnitudes very rapidly.

Applications for DS1721 include personal computers/services, cellular telephones, office equipment, or any microprocessor-based, thermally sensitive system.

, is active when the temperature of the device exceeds a user-defined

OUT

is configurable by the

OUT

1 of 16 111999

DETAILED PIN DESCRIPTION Table 1

PIN SYMBOL DESCRIPTION

1SDAData input/output pin. For 2-wire serial communication port. 2SCLClock input/output pin. For 2-wire serial communication port. 3T

OUT

Thermostat output. Active when temperature exceeds TH; will reset when

temperature falls below TL. 4 GND 5A2 6A1 7A0

Ground pin.

Address input pin.

8VDDSupply Voltage. 2.7V to 5.5V input power pin.

OVERVIEW

A block diagram of the DS1721 is shown in Figure 1. The DS1721 consists of five major components:

1. Precision temperature sensor

2. Analog-to-digital converter

3. 2-wire interface electronics

DS1721

4. Data registers

5. Thermostat comparator The factory-calibrated temperature sensor requires no external components. Upon power-up, the DS1721

is in an idle mode. Upon issuance of a Start Convert T command [51h], the DS1721 begins temperature conversions with the default resolution of 12 bits (0.0625°C resolution). Following an 8-bit command protocol, temperature data can be read over the 2-wir e interfa ce. The host can p eriodical l y read the valu e 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 DS1721 in a “one-shot” mode, under which the sensor will complete and store one temperature conversion and return to a low-power standby state. In time-sensitive applications, the user can change the conversion resolution from 12 bits to 9, 10, or 11. Each additional bit of resolution approximately doubles the conversion time, so 9-bit conversions can be performed in less than a quarter of a second.

This is accomplished by issuing a command protocol t o the configuration register. It is recommend ed t hat the user issue the command protocol to program the configuration register before any temperature conversion commands are issued after power-up. This is due to the fact that the configuration data is stored in volatile memory and will always power-up in the default state. The configuration register defines the conversion mode, thermometer resolution/conversion time, and active stat e of the thermostat comparator output. It also contains 3 status bits denoting the state of temperature conversions and thermostat flags.

The user can also program over-temperature (TH) and under-temper ature (TL) setpoints for thermostatic operation. The power-up state of TH is 80°C and that for TL is 75°C. The result of each temperature conversion is compared with these setpoints. The thermostat output (T

) becomes active when the

OUT

measured temperature exceeds the programmed TH, and remains latched in the active state until

2 of 16

DS1721

temperature falls below TL. Thus, any hysteresis can be realized for fan control without external components.

Digital data is written to/read from the DS1721 via a 2-wire interface, and all communication is MSb first. Multipoint sensing is possible with the DS1721 by uniquely setting the 3-bit address of up to eight parts on the 2-wire bus.

DS1721 FUNCTIONAL BLOCK DIAGRAM Figure 1

3 of 16

DS1721

OPERATION-Measuring Temperature

The core of DS1721 functionality is its direct-to-digital temperature sensor. The DS1721 measures temperature through the use of an on-chip temperature measurement technique with an operation range from -55°C to +125°C. The device can be configured to perform continuous conversions with the most recent result being stored in the thermometer register. The device can also be configured to perform a single conversion, store the result, and return to a standby mode. Regardless of the mode used, the digital temperature is retrieved from the temperature register using the Read Temperature (AAh) command, as described in detail in the “Command Set” section. The DS1721 power-up default has the s ensor set to automatically perform 12-bit conversions continuously once the Start Convert T (51h) command is issued. Details on how to change the settings after power-up are contained in the “OPERATIONProgramming” section.

The resolution of the temperature conversion can be configured as 9, 10, 11, or 12 bits, with 12-bit readings as 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 by issuing a Read Temperature (AAh) command. Table 2 describes the exact relationship of output data to measured temperature. The table assumes the DS1721 is configured for 12-bit resolution; if the device is configured in a lower resolution mode, insignificant 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.

TEMPERATURE/DATA RELATIONSHIPS Table 2

S262

MSb (UNIT = °C) LSb

-1

-2

-3

TEMP DIGITAL OUTPUT

+125°C 0111 1101 0000 0000 7D00h

+25.0625°C 0001 1001 0001 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

-4

MSB

0000LSB

DIGITAL OUTPUT

(Binary)

(Hex)

OPERATION-Thermostat Control

In its operating mode, the DS1721 functions as a thermostat with programmable hysteresis, as sho wn in Figure 2. The thermostat output updates as soon as a temperature conversion is complete. When the DS1721’s temperature meets or exceeds the value stored in the high temperature trip register (TH), the output becomes active, and will stay active until the temperature is equal to or below the temperature stored in the low temperature trigger register (TL). In this way, any amount of hysteresis may be obtained.

4 of 16

DS1721

The active state for the totem-pole output is programmable by the user. The power-up default of the DS1721 has TH=80°C, TL=75°C, and the output state active high. Refer to the “OPERATIONProgramming” section for instructions in adjusting the thermostat setpoints and T

active state.

COM

THERMOSTAT OUTPUT OPERATION Figure 2

OPERATION-Programming

There are two areas of interest in programming the DS1721: the Configuration/Status register and the thermostat setpoints. All programming is done via the 2-wire interface using the protocols discussed in the “Command Set” section.

Configuration/Status Register Programming

The configuration/status register is accessed via the Access Config (ACh) function command. Writing to or reading from the register is determined by the R/W bit of the 2-wire cont rol byte (See “2-wire S erial

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 DS1721 functionality is described below along with the power-up state of the bit and its ability to be read or written to. The entire register is volatile and will always power-up in the default state. Therefore, it is recommended that the user issue any configuration programming commands immediately after power is cycled, before any other commands are issued.

CONFIGURATION/STATUS REGISTER Figure 3

DONE X X U R1 R0 POL 1SHOT

MSb LSb

1SHOT = Temperature Conversion Mode. If 1SHOT is "1", the DS1721 will perform and store one temperature conversion upon reception of the Start Convert T (51h) command. If 1SHOT is "0", the DS1721 will continuously perform temperature conversions and store the last completed result in the Thermometer Register. The user has read/write access to the bit and the power-up default state is "0" (continuous mode).

POL = TCOM Polarity Bit. If POL is "1", the active state of the TCOM 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 "1" (active high).

U = Undefined. This bit is used internally by the DS1721. It will be a "0" at power-up and will change to a "1" once the Start Convert T [51h] command is issued. This is a “Don’t Care” on a write; i.e. The DS1721 will ignore writes to this location.

5 of 16

DS1721

R0, R1 = Thermometer Resolution Bits. Table 3 below defines the resolution of the digital thermometer, based on the settings of these two bits. There is a direct tradeoff between resolution and conversion time, as depicted in the DC Electrical Characteristics: Digital Thermometer table. The designer has read/write access to R0 and R1, and the default state is R0="1" and R1="1" (12-bit conversions).

THERMOMETER RESOLUTION CONFIGURATION Table 3

MAX

THERMOMETER

R1 R0

RESOLUTION

0 0 9-BIT 0.15s 0 1 10-BIT 0.3s 1 0 11-BIT 0.6s 1 1 12-BIT 1.2s

X = Undefined. These bits are used internally by the DS1721.

DONE = Temperature Conversion Status Bit. "1" = conversion complete and "0" = conversion in

progress. The DONE bit is read-only, and the power-up state is "1". In the continuous conversion mode, DONE = "0".

CONVERSION

TIME

Thermostat Setpoints Programming

The thermostat registers (TH and TL) define the setpoints for operation of the TCOM output. The respective register can be accessed ov er the 2-wire bus via the Access TH (A1h) or Access TL (A2h)

commands. Reading from or writing to the respective register is controlled by the state of the R/W bit in the 2-wire control byte (See “2-Wire Serial Data Bus” section).

The format of the TH and TL registers is a 12-bit 2’s complement representation of the temperature in °C. The user can program the number of bits (9, 10, 11, or 12) fo r each TH and TL that cor respond to the thermometer resolution configuration chosen. If the 9-bit mode is chosen, for example, the 3 least significant bits of TH and TL will be ignored by the thermostat comparator. The format for both TH and TL is shown in Figure 4. The power-up default of TH is 80°C and that for TL is 75°C.

TEMPERATURE/DATA RELATIONSHIPS Figure 4

S262

MSb (UNIT = °C) LSb

-1

-2

-3

TEMP DIGITAL OUTPUT

+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

-4

MSB

0000LSB

DIGITAL OUTPUT

(Binary)

(Hex)

6 of 16

DS1721

If the user does not wish to take advantage of the thermostat capabilities of the DS1721, the 24 bits can be used for general storage of system data that need not be maintained following a power loss. However, the T

pin should be left floating if general data is stored in TH/TL.

OUT

2-WIRE SERIAL DATA BUS

The DS1721 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 cont roll ed 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 DS1721 operates as a slave on the 2-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 5):

• 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 acknowled ges with a 9 bit.

Within the bus specifications a regular mode (100 kHz clock rate) and a fast mode (400 kHz clock rate) are defined. The DS1721 works in both modes.

Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowled ge 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.

7 of 16

DS1721

DATA TRANSFER ON 2-WIRE SERIAL BUS Figure 5

Figure 6 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:

Data transfer from a master trans mitter to a slave receiver. The 1

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.

Data transfer from a slave transmitter to a master receiver. The 1st 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 DS1721 may operate in the following two modes:

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 r eception of the slave address and direction bit.

Slave transmitter mode: The first b yte is received and handled as in the slave receiv er mode. However, in this mode, the direction bit will indicate that the transfer direction is reversed. Serial data is transmitted on SDA by the DS1721 while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer.

8 of 16

2-WIRE SERIAL COMMUNICATION WITH DS1721 Figure 6

DS1721

9 of 16

DS1721

SLAVE ADDRESS

A control byte is the 1st byte received following the START condition from the master device. The control byte consists of a 4-bit control code; for the DS1721, this is set as 1001 binary for r ead and write operations. The next 3 bits of the control byte are the device select bits (A2, A1, A0). They are used b y the master device to select which of eight devices are to be accessed. The s et bits are in effect the 3 l east

significant bits of the slave address. The last bit of the control byte (R/ W ) defines th e operation to be performed. When set to a 1 a read operation is selected, and when s et to a 0 a writ e operati on is selected. Following the START condition, the DS1721 monitors the SDA bus checking the device type identifier being transmitted. Upon receiving the 1001 code and appropriate device select bits, the slave device outputs an acknowledge signal on the SDA line.

COMMAND SET

Data and control information is read from and written to the DS1721 in the format shown in Figure 6. To write to the DS1721, the master will issue the slave address of the DS1721 and the R/W bit will be set to

"0". After receiving an acknowledge, the bus master provides a command protocol. Aft er receiving this protocol, the DS1721 will issue an acknowledge and the master may send data to the DS1721. If the DS1721 is to be read, the master must send the command protocol as before then issue a repeated START

condition and the control byte again, this time with the R/ W bit set to "1" to allow reading of the data from the DS1721. The command set for the DS1721 as shown in Table 4 is as follows:

Read Temperature [AAh]

This command reads the last temperature conversion result from the Thermometer Register in the format described in the “OPERATION-Measuring Temperature” section. If one’s application can accept thermometer resolution of only 1.0°C, the master only must read the first data b yte and follow with a NACK and STOP. For higher resolution, both bytes must be read.

Access TH [A1h]

If R/ W is "0", this command writes to the TH register. After issuing this command, the next 2 bytes written to the DS1721, in the format described for thermostat set-points, will set the high temperature

threshold for operation of the TOUT output. If R/W is "1", the value stored in this register is read back.

Access TL [A2h]

If R/ W is "0", this command writes to the TL register. After issuing this command, the next 2 bytes written to the DS1721, in the format described for thermostat set-points, will set the high temperature

threshold for operation of the TOUT output. If R/

W is "1", the value stored in this register is read back.

Access Config [ACh]

If R/ W is "0", this command writes to the configuration register. After issuing this command, the next data byte value is to be written into the configuration register. If R/W is "1", the next data byte read is the

value stored in the configuration register.

Start Convert T [51h]

This command begins a temperature conversion. No further data is required. In one-shot mode, the temperature conversion will be performed and stored and then the DS1721 will remain idle. In continuous mode, this command will initiate continuous conversions.

10 of 16

DS1721

Stop Convert T [22h]

This command stops temperature conversion. No further data is required. This command may be used to halt a DS1721 in continuous conversion mode. After issuing this command, the current temperature measurement will be completed, stored and the DS1721 will remain idle until a Start Convert T is issued to resume conversions.

DS1721 COMMAND SET Table 4

2-WIRE BUS DATA

INSTRUCTION DESCRIPTION PROTOCOL

Access Configuration

Access TH

Access TL

Start Convert T

Stop Convert T Read

Temperature

Writes to/Reads from 8-bit configuration/status register Writes to/Reads from 12-bit TH register Writes to/Reads from 12-bit TL register

CONVERSION COMMANDS

Initiates temperature conversion Terminates continuous conversions Reads 12-bit Temperature register

ACh 1 data byte 1

A1h 1 or 2 data bytes 1, 3

A2h 1 or 2 data bytes 1, 3

51h idle 2

22h idle 2

AAh Read 1 or 2 data bytes 3

AFTER ISSUING

PROTOCOL

NOTES

NOTES:

1. Data direction depends upon R/W bit in the 2-wire control byte.

2. In continuous conversion mode, a Stop Convert T command will halt continuous conversion. To

restart, the Start Convert T command must be issued. In one-shot mode, a Start Convert T command must be issued for every temperature reading desired.

3. If the user only desires 8-bit thermometer readings, the master need only read 1 data byte and follow

with a NACK and STOP. If higher resolution is required, 2 bytes must be read.

11 of 16

SAMPLE COMMAND SEQUENCE Table 5

Example: After power-up, initiates a temperature conversion, bus master reads temperature

BUS MASTER

MODE

TX RX START Bus Master initiates a START condition TX RX <address, 0>

RX TX ACK DS1721 generates acknowledge bit TX RX 51h Bus Master sends start convert T protocol RX TX ACK DS1721 generates acknowledge bit TX RX START Bus Master initiates a repeated START condition TX RX <address, 0>

RX TX ACK DS1721 generates acknowledge bit TX RX AAh Bus Master sends read temperature protocol RX TX ACK DS1721 generates acknowledge bit TX RX START Bus Master initiates a repeated START condition TX RX <address, 1>

RX TX ACK DS1721 generates acknowledge bit RX TX <1 data byte> DS1721 transmits MSB of temperature TX RX ACK Bus Master generates acknowledge bit RX TX <1 data byte> DS1721 transmits LSB of temperature

DS1721

MODE

DATA (MSB

FIRST)

COMMENTS

Bus Master sends DS1721 address; R/

W = 0

Bus Master sends DS1721 address; R/W =1

DS1721

12 of 16

DS1721

SAMPLE COMMAND SEQUENCE Table 6

Example: Bus master programs the DS1721 for 11-bit conversions in the continuous mode with an active low state for the thermostat output. It then programs TH=50°C and TL=45°C and starts temperature conversions.

BUS MASTER

MODE

TX RX START Bus Master initiates a START condition TX RX <address, 0>

RX TX ACK DS1721 generates acknowledge bit TX RX ACh Bus Master sends access configuration protocol RX TX ACK DS1721 generates acknowledge bit TX RX 08h Bus Master programs configuration register as

RX TX ACK DS1721 generates acknowledge bit

TX RX START Bus Master Initiates a REPEATED START

TX RX <address, 0> RX TX ACK DS1721 generates acknowledge bit

TX RX A1h Bus Master sends access TH protocol RX TX ACK DS1721 generates acknowledge bit TX RX 32h Bus Master writes MSB of TH (50°C) RX TX ACK DS1721 generates acknowledge bit TX RX 00h Bus Master writes LSB of TH (50°C) RX TX ACK DS1721 generates acknowledge bit

DS1721

MODE

DATA (MSB

FIRST)

COMMENTS

Bus Master sends DS1721 address; R/

W = 0

described above. This will also clear thermostat flags

condition Bus Master sends DS1721 address; R/W = 0

TX RX START Bus Master initiates a REPEATED START

condition

TX RX <address, 0>

Bus Master sends DS1721 address; R/W = 0 RX TX ACK DS1721 generates acknowledge bit TX RX A2h Bus Master sends access TL protocol RX TX ACK DS1721 generates acknowledge bit TX RX 2Dh Bus Master writes MSB of TL (45°C) RX TX ACK DS1721 generates acknowledge bit TX RX 00h Bus Master writes LSB of TL (45°C) RX TX ACK DS1721 generates acknowledge bit

TX RX START Bus Master initiates a REPEATED START

condition TX RX <address, 0>

Bus Master sends DS1721 address; R/W = 0 RX TX ACK DS1721 generates acknowledge bit TX RX 51h Bus Master sends start convert protocol RX TX ACK DS1721 generates acknowledge bit TX RX STOP Bus Master initiates STOP condition

13 of 16

DS1721

ABSOLUTE MAXIMUM RATINGS*

Voltage on VDD, Relative to Ground -0.3V to +7.0V Voltage on any other pin, Related to Ground -0.3V to +7.0V Operating Temperature -55°C to +125°C Storage Temperature -55°C to +125°C Soldering Temperature 260°C for 10 seconds

* 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.

RECOMMENDED DC OPERATING CONDITIONS

(-55°C to +125°C; 2.7V ≤ V

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Supply Voltage V

2.7 5.5 V 1

≤ 5.5V)

DC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; 2.7V ≤ VDD ≤ 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Input Logic High V

Input Logic Low V

SDA Output Logic Low Voltage

Output Logic

OUT

Voltage

Input Current Each I/O Pin

I/O Capacitance C Standby Current I

Active Current I

OL1

OL2

I/O

DD1

3 mA sink

current

6 mA sink

current

1 mA source

current

4 mA sink

current

0.4V ≤ V ≤ 0.9 V

I/O

Active Temp.

Conversions

Communication

only

0.7

-0.5

0 0.4 V 1

0 0.6 V 1

2.4 V 1

-10 +10 µA 2

+0.5

0.3

0.4 V 1

10 pF

1 µA 3, 4

1000 µA 3, 4

100 µA 3, 4

14 of 16

DC ELECTRICAL CHARACTERISTICS:

DS1721

DIGITAL THERMOMETER (-55°C to +125°C; 2.7V ≤ V

≤ 5.5V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

DS1721 Thermometer Error

ERR

-10°C to +85°C ±1.0 °C 5

Resolution 9 12 bits

Conversion Time t

CONVT

9-bit

Conversions

10-bit

Conversions

11-bit

Conversions

12-bit

Conversions

125 150

250 300

500 600

1000 1200

AC ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE (-55°C to +125°C; V

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

SCL Clock Frequency

SCL

Bus Free Time Between a STOP and START

BUF

Condition Hold Time (Repeated) START

HD:STA

Condition Low Period of SCL Clock High Period of SCL Clock

LOW

HIGH

Setup Time for a Repeated START

SU:STA

Condition Data Hold Time t

Data Set-up Time t

HD:DAT

SU:DAT

Rise Time of both SDA and SCL Signals Fall Time of both SDA and SCL Signals Set-up time for STOP Condition Capacitive Load for each Bus Line

SU:STO

Input Capacitance C

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

Fast Mode

Standard Mode

15 of 16

0 0

1.3

4.7

0.6

4.0

1.3

4.7

0.6

4.0

0.6

4.7 0

100 250

20+0.1

0.6

4.0

400 100

0.9 µs 7

300

1000

300

1000

400 pF 9

5pF

=2.7V to 5.5V)

KHz

µs

µs 6

µs

ns 8

ns 9

µs

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.

DS1721

3. I

4. I

specified with T

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

pin open.

OUT

5. See typical accuracy curves for specification limits outside the temperature range indicated.

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

7. The maximum t

HD:DAT

has only to be met if the device does not stretch the LOW period (t

LOW

SCL signal.

8. A fast mode device can be used in a standard mode system, but the requirement t

>250 ns must

SU:DAT

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+t

1000+250 = 1250 ns before the SCL line is released.

SU:DAT

9. Cb - total capacitance of one bus line in pF.

TIMING DIAGRAMS Figure 7

) of the

TYPICAL DS1721 THERMOMETER PERFORMANCE CURVE Figure 8

TBD

16 of 16

Rainbow Electronics DS1721 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual