ds1620.pdf

DS1620

Digital Thermometer and Thermostat

www.dalsemi.com

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 1

second (max)

Thermostatic settings are user-definable and

nonvolatile

Data is read from/wri tten 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

V DD

CLK/CONV

T HIGH

RST

T LOW

GND

T COM

DS1620S 8-Pin SOIC (208-miil)

See Mech Drawings Section

V DD

CLK/CONV

T HIGH

RST

T LOW

GND

T COM

DS1620 8-Pin DIP (300-mil)

See Mech Drawings Section

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

- High Temperature Trigger

T COM

- High/Low Combination Trigger

V DD

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

TH. T LOW is driven high if the DS1620’s temperature is less than or equal to a user–defined temperature

TL. T COM is driven high when the temperature exceeds TH and stays high until the temperature falls

below that of TL.

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072099

T LOW

- Low Temperature Trigger

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.

OPERATION-MEASURING TEMPERATURE

A block diagram of the DS1620 is shown in Figure 1. The DS1620 measures temperatures through the

use of an onboard proprietary temperature measurement technique. A block diagram of the temperature

measurement circuitry is shown in Figure 2.

The DS1620 measures temperature by counting the number of clock cycles that an oscillator with a low

temperature coefficient goes through during a gate period determined by a high temperature coefficient

oscillator. The counter is preset with a base count that corresponds to –55C. If the counter reaches 0

before the gate period is over, the temperature register, which is also preset to the –55C value, is

incremented, indicating that the temperature is higher than –55C.

At the same time, the counter is then preset with a value determined by the slope accumulator circuitry.

This circuitry is needed to compensate for the parabolic behavior of the oscillators over temperature. The

counter is then clocked again until it reaches 0. If the gate period is still not finished, then this process

repeats.

The slope accumulator is used to compensate for the nonlinear behavior of the oscillators over

temperature, yielding a high-resolution temperature measurement. This is done by changing the number

of counts necessary for the counter to go through for each incremental degree in temperature. To obtain

the desired resolution, therefore, both the value of the counter and the number of counts per degree C (the

value of the slope accumulator) at a given temperature must be known.

DS1620 FUNCTIONAL BLOCK DIAGRAM Figure 1

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DS1620

TEMPERATURE MEASURING CIRCUITRY Figure 2

SLOPE ACCUMULATOR

PRESET

COMPARE

LOW TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

PRESET

SET/CLEAR

LSB

INC

TEMPERATURE REGISTER

HIGH TEMPERATURE

COEFFICIENT OSCILLATOR

COUNTER

STOP

This calculation is done inside the DS1620 to provide 0.5C resolution. The temperature reading is

provided in a 9–bit, two’s complement reading by issuing a READ TEMPERATURE command. 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 DS1620 can measure temperature over the range of

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

used.

TEMPERATURE/DATA RELATIONSHIPS Table 1

TEMP

DIGITAL OUTPUT

(Binary)

DIGITAL OUTPUT

(Hex)

+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

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 9 th (MSB) bit), or as two transfers of 8–bit

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DS1620

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

the DS1620 will output 0s.

Note that temperature is represented in the DS1620 in terms of a ½C LSB, yielding the following 9–bit

format:

MSB

LSB

T = -25°C

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 +

(COUNT_PER

COUNT_REMA

IN)

COUNT_PER_

DETAILED PIN DESCRIPTION Table 2

SYMBOL

DESCRIPTION

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

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 use d as a convert

pin. Temperature conversion will begin on the falling edge of CONV .

RST

Reset input pin for 3-wire communication port.

GND

Ground pin.

T COM

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

will reset to low when temperature falls below TL.

T LOW

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

T HIGH

High Temperature Trigger. Goes high when temperature exceeds TH.

V DD

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

OPERATION–THERMOSTAT CONTROLS

Three thermally triggered outputs, T HIGH , T LOW , and T COM , are provided to allow the DS1620 to be used

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 HIGH becomes active (high) and remains active until the

DS1620’s measured temperature becomes less than the stored value in the high temperature register, TH.

The T HIGH output can be used to indicate that a high temperature tolerance boundary has 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.

The T LOW output functions similarly to the T HIGH output. When the DS1620’s measured temperature

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

T LOW remains active until the DS1620’s temperature becomes greater than the value stored in the low

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

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DS1620

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

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

THERMOSTAT OUTPUT OPERATION Figure 3

T HIGH

T LOW

T COM

T(°C)

OPERATION AND CONTROL

The DS1620 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 DS1620 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

DONE

THF

TLF

NVB

CPU

1SHOT

where

DONE = Conversion Done Bit. 1=conversion complete, 0=conversion in progress.

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

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. 1=write to an E 2 memory cell in progress. 0=nonvolatile

memory is not busy. A copy to E 2 may take up to 10 ms.

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

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