DS1620R - Dallas Semiconductor

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FEATURES

§ Requires no external components

§ Measures temperatures from -55°C to +125°C

in 0.5°C increments. Fahrenheit equivalent is

-67°F to 257°F in 0.9°F increments

§ Temperature is read as a 9-bit value

§ Converts temperature to digital word in 200

ms, typically

§ Thermostatic settings are user-definable and

nonvolatile

§ Internal 50-ohm resistor provides self heating

§ Data is read from/written via a 3-wire serial

interface (CLK, DQ, RST )

§ Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

§ 16-pin SOIC package

PIN ASSIGNMENT

PIN DESCRIPTION

DQ - 3-Wire Input/Output

CLK/CONV - 3-Wire Clock Input and

Standalone Convert Input

RST - 3-Wire Reset Input

GND - Ground

RA - Connection to Internal 50Ω

Resistor

RB - Connection to Internal 50Ω

Resistor

THIGH - High Temperature Trigger

TLOW - Low Temperature Trigger

TCOM - High/Low Combination Trigger

VDD - Power Supply Voltage (+5V)

DESCRIPTION

The DS1620R Self–Heating Temperature Sensor provides 9–bit temperature readings which indicate the

temperature of the device. The internal 50-ohm resistor acts as the self–heating element. Predictable self–

heating characteristics allow users to model temperature rise of active components in their system,

allowing monitoring of airflow and other thermal management parameters. With three thermal alarm

outputs, the DS1620R can also act as a thermostat. THIGH is driven high if the DS1620R’s temperature

exceeds a user-defined temperature TH. TLOW is driven high if the DS1620R’s temperature falls below a

user-defined temperature TL. TCOM is driven high when the temperature exceeds TH, and stays high until

the temperature falls below that of TL.

DS1620R

Self-Heating Temperature Sensor

www.dalsemi.com

DS1620R

16-Pin SOIC (300-MIL)

COM

CLK/CONV

RST

GND

DS1620R

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User-defined temperature settings are stored in nonvolatile memory, so parts may be programmed prior to

insertion in a system, as well as used in standalone applications without a CPU. Temperature settings and

temperature readings are all communicated to/from the DS1620R over a simple 3–wire interface.

OPERATION – READING TEMPERATURE

The DS1620R measures temperatures through the use of an onboard proprietary temperature

measurement technique. The temperature reading is provided in a 9–bit, two’s complement reading. Table

1 describes the exact relationship of output data to measured temperature. The data is transmitted serially

through the 3–wire serial interface, LSB first. The DS1620R can measure temperature over the range of

-55°C to +125°C in 0.5°C increments. For Fahrenheit usage, a lookup table or conversion factor must be

used.

Since data is transmitted over the 3–wire bus LSB first, temperature data may be written to/read from the

DS1620R as either a 9–bit word (asserting RST after the 9th (MSB) bit), or as two transfers of 8–bit

words, with the most significant 7 bits being ignored or set to 0, as illustrated in Table 1.

Note that temperature is represented in the DS1620R in terms of a ½°C LSB, yielding the following 9–bit

format:

TEMPERATURE/DATA RELATIONSHIPS Table 1

TEMP DIGITAL OUTPUT

(Binary) DIGITAL OUTPUT

(Hex)

+125°C 00000000 11111010 00FA

+25°C 00000000 00110010 0032h

½°C 00000000 00000001 0001h

0°C 00000000 00000000 0000h

-½°C 00000001 11111111 01FFh

-25°C 00000001 11001110 01CEh

-55°C 00000001 10010010 0192h

MSB

LSB

T = -25°C

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DS1620R FUNCTIONAL BLOCK DIAGRAM Figure 1

DETAILED PIN DESCRIPTION Table 2

PIN SYMBOL DESCRIPTION

1 DQ Data Input/Output pin for 3-wire communication port.

2CLK/CONV Clock input pin for 3-wire communication port. When the DS1620 is used in a

standalone application with no 3–wire port, this pin can be used as a convert pin.

Temperature conversion will begin on the falling edge of CONV.

3 NC No internal connection

4RST Reset input pin for 3-wire communication port.

5 GND Ground pin

6 RA Connection to one side of internal 50 ohm resistor

7 NC No internal connection

8 NC No internal connection

9 NC No internal connection

10 NC No internal connection

11 RB Connection to one side of internal 50 ohm resistor

12 TCOM High/Low Combination Trigger. Goes high when temperature exceeds TH;

will reset to low when temperature falls below TL.

13 TLOW Low Temperature Trigger. Goes high when temperature falls below TL.

14 NC No internal connection

15 THIGH High Temperature Trigger. Goes high when temperature exceeds TH.

16 VDD Supply Voltage. 5V input power pin.

OPERATION – THERMOSTAT CONTROLS

Three thermally triggered outputs, THIGH, TLOW , and TCOM , are provided to allow the DS1620R to be used

as a thermostat, as shown in Figure 2. When the DS1620R’s temperature meets or exceeds the value

stored in the high temperature trip register, the output THIGH becomes active (high) and remains active

until the DS1620R’s measured temperature becomes less than the stored value in the high temperature

been met or exceeded, or it can be used as part of a closed loop system to activate a cooling system and

deactivate it when the system temperature returns to tolerance.

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The TLOW output functions similarly to the THIGH output. When the DS1620R’s measured temperature

equals or falls below the value stored in the low temperature register, the TLOW output becomes active.

TLOW remains active until the DS1620R’s temperature becomes greater than the value stored in the low

temperature register, TL. The TLOW output can be used to indicate that a low temperature tolerance

boundary has been met or exceeded, or as part of a closed loop system it can be used to activate a heating

system and to deactivate it when the system temperature returns to tolerance.

The TCOM output goes high when the measured temperature exceeds TH, and will stay high until the

temperature falls below TL. In this way, any amount of hysteresis may be obtained.

THERMOSTAT OUTPUT OPERATION Figure 2

OPERATION AND CONTROL

The DS1620R must have temperature settings resident in the TH and TL registers for thermostatic

operation. A configuration/status register also determines the method of operation that the DS1620R will

use in a particular application and indicates the status of the temperature conversion operation.

The configuration register is defined as follows:

CONFIGURATION/STATUS REGISTER

where

DONE = Conversion Done bit. 1=Conversion complete, 0=Conversion in progress. In continuous

conversion mode, the bit will always be 0. In one–shot mode, this bit should be checked prior to

attempting to read the temperature to ensure that the conversion is complete.

THF = Temperature High Flag. This bit will be set to 1 when the temperature is greater than or equal

to the value of TH. It will remain 1 until reset by writing 0 into this location or by removing power from

the device. This feature provides a method of determining if the DS1620 has ever been subjected to

temperatures above TH while power has been applied.

TLF = Temperature Low Flag. This bit will be set to 1 when the temperature is less than or equal to

the value of TL. It will remain 1 until reset by writing 0 into this location or by removing power from the

DONE THF TLF NVB 1 0 CPU 1SHOT

THIGH

TLOW

TCOM

T(°C)

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device. This feature provides a method of determining if the DS1620 has ever been subjected to

temperatures below TL while power has been applied.

NVB = Nonvolatile Memory Busy Flag. This bit will be a 1 while a write to E2 memory is in

progress; 0=nonvolatile memory not busy. A write to E2 memory typically takes 10 ms, but may take up

to 50 ms at high temperatures.

CPU = CPU use bit. If CPU=0, the CLK/CONV pin acts as a conversion start control when RST is

low. If CPU is 1, the DS1620 will be used with a CPU communicating to it over the 3–wire port and the

operation of the CLK/CONV pin is as a normal clock in concert with DQ and RST. This bit is stored in

nonvolatile E2 memory, capable of at least 50,000 writes.

1SHOT = One–Shot Mode. If 1SHOT is 1, the DS1620 will perform one temperature conversion upon

reception of the Start Convert T protocol. If 1SHOT is 0, the DS1620 will continuously perform

temperature conversion. This bit is stored in nonvolatile E2 memory, capable of at least 50,000 writes.

For typical thermostat operation, the DS1620R will operate in continuous mode. However, for

applications where only one reading is needed at certain times or to conserve power, the one–shot mode

may be used. Note that the thermostat outputs (THIGH, TLOW, TCOM) will remain in the state they were in

after the last valid temperature conversion cycle when operating in one–shot mode.

OPERATION IN STAND–ALONE MODE

In applications where the DS1620R is used as a simple thermostat, no CPU is required save for

programming the temperature limits. Since the temperature limits are nonvolatile, the DS1620R may be

programmed prior to insertion in the system. In order to facilitate operation without a CPU, the

CLK/CONV pin (pin 2) may be used to initiate conversions. Note that the CPU bit must be set to 0 in the

configuration register to use this mode of operation.

To use the CLK/CONV pin to initiate conversions, RST must be low and CLK/CONV must be high. If

CLK/ CONV is driven low and then brought high in less than 10 ms, one temperature conversion will be

performed and then the DS1620 will return to an idle state. If CLK/ CONV is driven low and remains

low, continuous con-versions will take place until CLK/CONV is brought high again. With the CPU bit

set to 0, the CLK/CONV will override the 1 SHOT bit if it is equal to 1. This means that even if the part

is set for one–shot mode, driving CLK/ CONV low will initiate conversions.

INTERNAL RESISTOR

The internal 50-ohm resistor is connected between pins RA and RB. A typical application will use this

resistor connected between 5V and ground, providing a 500-mW power dissipation in the resistor. In still

air this will cause an approximately 40°C temperature rise in the DS1620R. Under other airflow

conditions this temperature rise will be different, giving some indication as to how much heat is

conducted away from the device by the airflow. The actual temperature rise and thermostat settings for

use in a particular system will therefore be dictated by the system’s design and protection requirements

and must be characterized by the user.

Because the DS1620R measures the actual die temperature of the device, its measurement range is from

-55°C to +125°C; however, since the internal resistor is causing a temperature rise in the device, the

entire DS1620R is rated for operation in ambient temperatures of –40°C to +85°C only.

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3–WIRE COMMUNICATIONS

The 3–wire bus is comprised of three signals. These are the RST (reset) signal, the CLK (clock) signal,

and the DQ (data) signal. All data transfers are initiated by driving the RST input high. Driving the RST

input low terminates communication. (See Figures 3 and 4.)

A clock cycle is a sequence of a falling edge followed by a rising edge. For data inputs, the data must be

valid during the rising edge of a clock cycle. Command bits and data bits are output on the falling edge of

the clock and remain valid through the rising edge.

When reading data from the DS1620R, the DQ pin goes to a high impedance state while the clock is high.

Taking RST low will terminate any communication and cause the DQ pin to go to a high impedance

state.

Data over the 3–wire interface is communicated LSB first.

The command set for the 3–wire interface as shown in Table 3 is as follows:

Read Temperature [AAh]

This command reads the contents of the register which contains the last temperature conversion result.

The next nine clock cycles will output the contents of this register.

Write TH [01h]

This command writes to the TH (HIGH TEMPERATURE) register. After issuing this command the next

9 clock cycles clock in the 9–bit temperature limit which will set the threshold for operation of the THIGH

output.

Write TL [02h]

This command writes to the TL (LOW TEMPERATURE) register. After issuing this command the next

nine clock cycles clock in the 9–bit temperature limit which will set the threshold for operation of the

TLOW output.

Read TH [A1h]

This command reads the value of the TH (HIGH TEMPERATURE) register. After issuing this command

the next nine clock cycles clock out the 9–bit temperature limit which sets the threshold for operation of

the THIGH output.

Read TL [A2h]

This command reads the value of the TL (LOW TEMPERATURE) register. After issuing this command

the next nine clock cycles clock out the 9–bit temperature limit which sets the threshold for operation of

the TLOW output.

Start Convert T [EEh]

This command begins a temperature conversion. No further data is required. In one–shot mode the

temperature conversion will be performed and then the DS1620R will remain idle. In continuous mode

this command will initiate continuous conversions.

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Stop Convert T [22h]

This command stops temperature conversion. No further data is required. This command may be used to

halt a DS1620R in continuous conversion mode. After issuing this command the current temperature

measurement will be completed and then the DS1620R will remain idle until a Start Convert T is issued

to resume continuous operation.

Write Config [0Ch]

This command writes to the configuration register. After issuing this command the next eight clock cycles

clock in the value of the configuration register.

Read Config [ACh]

This command reads the value in the configuration register. After issuing this command the next eight

clock cycles output the value of the configuration register.

DS1620R COMMAND SET Table 3

INSTRUCTION DESCRIPTION PROTOCOL

3-WIRE BUS

DATA AFTER

ISSUING

PROTOCOL NOTES

TEMPERATURE CONVERSION COMMANDS

Read Temperature Reads last converted temperature

value from temperature register. Aah <read data>

Start Convert T Initiates temperature conversion. Eeh idle 1

Stop Convert T Halts temperature conversion. 22h idle 1

THERMOSTAT COMMANDS

Write TH Writes high temperature limit value

into TH register. 01h <write data> 2

Write TL Writes low temperature limit value

into TL register. 02h <write data> 2

Read TH Reads stored value of high

temperature limit from TH register. A1h <read data> 2

Read TL Reads stored value of low

temperature limit from TL register. A2h <read data> 2

Write Config Writes configuration data to

configuration register. 0Ch <write data> 2

Read Config Reads configuration data from

configuration register. ACh <read data> 2

NOTES:

1. 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.

2. Writing to the E2 typically requires 10 ms at room temperature. After issuing a write command no

further writes should be requested for at least 10 ms.

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FUNCTION EXAMPLE

Example: CPU sets up DS1620R for continuous conversion and thermostatic function.

CPU MODE DS1620R

MODE

(3-WIRE) DATA (LSB FIRST) COMMENTS

TX RX Raise RST CPU raises RST to initiate transfer.

TX RX 0Ch CPU issues Write Config command.

TX RX 02h CPU sets DS1620R up for continuous

conversion.