MAXIM DS1620 User Manual

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DS1620

Digital Thermometer and

Thermostat

FEATURES

§ Requires no external components

§ Supply voltage range covers from 2.7V to

5.5V

§ 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 750

ms (max)

§ Thermostatic settings are user-definable and nonvolatile

§ 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

§ 8-pin DIP or SOIC (208-mil) packages

PIN ASSIGNMENT

CLK/CONV

RST

GND

DS1620S 8-Pin SOIC (208-mil)

CLK/CONV

RST

GND

DS1620 8-Pin DIP (300-mil)

HIGH

LOW

COM

HIGH

LOW

COM

PIN DESCRIPTION

DQ - 3-Wire Input/Output

CLK/CONV - 3-Wire Clock Input and

Stand-alone Convert Input

RST - 3-Wire Reset Input

GND - Ground T

- High Temperature Trigger

HIGH

- Low Temperature Trigger

LOW

- High/Low Combination Trigger

COM

VDD - Power Supply Voltage (3V - 5V)

DESCRIPTION

The DS1620 Digital Thermometer and Thermostat provides 9–bit temperature readings which indicate the temperature of the device. With three thermal alarm outputs, the DS1620 can also act as a thermostat. T

is driven high if the DS1620’s temperature is greater than or equal to a user–defined temperature

HIGH

TH. T TL. T below that of TL.

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is driven high if the DS1620’s temperature is less than or equal to a user–defined temperature

LOW

is driven high when the temperature exceeds TH and stays high until the temperature falls

COM

DS1620

User–defined temperature settings are stored in nonvolatile memory, so parts can 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 DS1620 over a simple 3–wire interface.

ORDERING INFORMATION

PART PACKAGE MARKING DESCRIPTION

DS1620

DS1620 8-Pin DIP (300 mil) DS1620+ DS1620 (See Note) Lead-Free 8-Pin DIP (300 mil) DS1620S DS1620 8-Pin SOIC (208 mil) DS1620S+ DS1620 (See Note) Lead-Free 8-Pin SOIC (208 mil) DS1620S/T&R DS1620 8-Pin SOIC (208 mil), 2000-Piece Tape-and-Reel DS1620S+T&R DS1620 (See Note) Lead-Free 8-Pin SOIC (208 mil), 2000-Piece

Tape-and-Reel

Note: A “+” symbol will also be marked on the package near the Pin 1 indicator

DETAILED PIN DESCRIPTION Table 1

PIN SYMBOL DESCRIPTION

1 DQ Data Input/Output pin for 3-wire communication port. 2

CLK/CONV

Clock input pin for 3-wire communication port. When the DS1620 is used in a stand-alone 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 .

RST

4 GND 5 T

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

COM

Reset input pin for 3-wire communication port.

Ground pin.

will reset to low when temperature falls below TL. 6 T 7 T

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

LOW

High Temperature Trigger. Goes high when temperature exceeds TH.

HIGH

8 VDD Supply Voltage. 2.7V – 5.5V input power pin.

Table 2. DS1620 REGISTER SUMMARY

(USER ACCESS)

Temperature (Read Only)

(Read/Write)

SIZE

9 Bits SRAM

9 Bits EEPROM

MEMORY

TYPE

AND POWER-UP/POR STATE

Measured Temperature (Two’s Complement) Power-Up/POR State: -60ºC (1 1000 1000) Upper Alarm Trip Point (Two’s Complement) Power-Up/POR State: User-Defined. Initial State from Factory: +15°C (0 0001 1110) Lower Alarm Trip Point (Two’s Complement) Power-Up/POR State: User-Defined. Initial State from Factory: +10°C (0 0001 0100)

OPERATION-MEASURING TEMPERATURE

A block diagram of the DS1620 is shown in Figure 1.

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DS1620

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DS1620 FUNCTIONAL BLOCK DIAGRAM Figure 1

The DS1620 measures temperature using a bandgap-based temperature sensor. The temperature reading is provided in a 9–bit, two’s complement reading by issuing a READ TEMPERATURE command. The data is transmitted serially through the 3–wire serial interface, LSB first. The DS1620 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 can be written to/read from the

DS1620 as either a 9–bit word (taking RST low 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 3. After the MSB, the DS1620 will output 0s.

Note that temperature is represented in the DS1620 in terms of a ½°C LSB, yielding the 9–bit format shown in Figure 2.

TEMPERATURE, TH, and TL REGISTER FORMAT Figure 2

MSB

T = -25°C

LSB

1 1 0 0 1 1 1 0

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DS1620

Table 3 describes the exact relationship of output data to measured temperature. .

TEMPERATURE/DATA RELATIONSHIPS Table 3

TEMP DIGITAL OUTPUT

(Binary)

+125˚C 0 11111010 00FA

+25˚C 0 00110010 0032h

+½˚C 0 00000001 0001h

+0˚C 0 00000000 0000h

-½˚C 1 11111111 01FFh

-25˚C 1 11001110 01CEh

-55˚C 1 10010010 0192h

Higher resolutions may be obtained by reading the temperature, and truncating the 0.5°C bit (the LSB) from the read value. This value is TEMP_READ. The value left in the counter may then be read by issuing a READ COUNTER command. This value is the count remaining (COUNT_REMAIN) after the gate period has ceased. By loading the value of the slope accumulator into the count register (using the READ SLOPE command), this value may then be read, yielding the number of counts per degree C (COUNT_PER_C) at that temperature. The actual temperature may be then be calculated by the user using the following:

TEMPERATURE=TEMP_READ-0.25 +

DIGITAL OUTPUT

(Hex)

IN)COUNT_REMA-_C(COUNT_PER

CCOUNT_PER_

OPERATION–THERMOSTAT CONTROLS

Three thermally triggered outputs, T as a thermostat, as shown in Figure 3. When the DS1620’s temperature meets or exceeds the value stored in the high temperature trip register, the output T DS1620’s measured temperature becomes less than the stored value in the high temperature register, TH. The T

output can be used to indicate that a high temperature tolerance boundary has been met or

HIGH

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.

The T

output functions similarly to the T

LOW

equals or falls below the value stored in the low temperature register, the T T

remains active until the DS1620’s temperature becomes greater than the value stored in the low

LOW

temperature register, TL. The T

LOW

boundary has been met or exceeded, or as part of a closed loop system it can be used to activate a heating system and deactivate it when the system temperature returns to tolerance.

The T

output goes high when the measured temperature meets or exceeds TH, and will stay high until

COM

the temperature equals or falls below TL. In this way, any amount of hysteresis can be obtained.

, T

HIGH

output can be used to indicate that a low temperature tolerance

LOW

, and T

HIGH

output. When the DS1620’s measured temperature

HIGH

, are provided to allow the DS1620 to be used

COM

becomes active (high) and remains active until the

output becomes active.

LOW

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