DS1620.PDF

DS1620

Digital Thermometer and Thermostat

FEATURES

•

PIN ASSIGNMENT

Requires no external components

V DD

•

Supply voltage range covers from 2.7V to 5.5V

CLK/C ONV

T HIGH

•

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

RST

T LOW

GND

T COM

DS1620S 8–PIN SOIC (208 MIL)

See Mech Drawings Section

•

Temperature is read as a 9–bit value

•

Converts temperature to digital word in 1 second

(max)

V DD

•

Thermostatic settings are user–definable and non–

volatile

CLK/C ONV

T HIGH

RST

T LOW

GND

T COM

•

Data is rea d fro m/written via a 3–wire serial interface

(CLK, DQ, RST)

DS1620 8–PIN PDIP (300 MIL)

See Mech Drawings Section

•

Applications include thermostatic controls, industrial

systems, consumer products, thermometers, or any

thermally sensitive system

PIN DESCRIPTION

– 3–Wire Input/Output

•

8–pin DIP or SOIC (208 mil) packages

CLK/CONV

– 3–Wire Clock Input and

Stand–alone

Convert Input

RST

– 3–Wire Reset Input

GND

– Ground

T HIGH

– High Temperature Trigger

T LOW

– Low Temperature Trigger

T COM

– High/Low Combination Trigger

V DD

– Power Supply Voltage (3V – 5V)

DESCRIPTION

The DS1620 Digital Thermometer and Thermostat pro-

vides 9–bit temperature readings which indicate the

temperature of the device. With three thermal alarm out-

puts, 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.

User–defined temperature settings are stored in non–

volatile memory, so parts can be programmed prior to

insertion in a system, as well as used in stand–alone

applications without a CPU. Temperature settings and

temperature readings are all communicated to/from the

DS1620 over a simple 3–wire interface.

030598 1/12

DS1620

OPERATION–MEASURING TEMPERATURE

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

The DS1620 measures temperatures through the use of

an on–board proprietary temperature measurement

technique. A block diagram of the temperature mea-

surement circuitry is shown in Figure 2.

At the same time, the counter is then preset with a value

determined by the slope accumulator circuitry. This cir-

cuitry is needed to compensate for the parabolic behav-

ior of the oscillators over temperature. The counter is

then clocked again until it reaches zero. If the gate

period is still not finished, then this process repeats.

The DS1620 measures temperature by counting the

number of clock cycles that an oscillator with a low tem-

perature coefficient goes through during a gate period

determined by a high temperature coefficient oscillator.

The counter is preset with a base count that corre-

sponds to –55

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 neces-

sary 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 accumu-

lator) at a given temperature must be known.

C value, is incremented, indicat-

ing that the temperature is higher than –55 ° C.

DS1620 FUNCTIONAL BLOCK DIAGRAM Figure 1

STATUS REGISTER &

CONTROL LOGIC

CLK

TEMPERATURE SENSOR

ADDRESS

AND

RESET

HIGH TEMP TRIGGER, TH

RST

T HIGH

LOW TEMP TRIGGER, TL

T LOW

DIGITAL COMPARATOR/LOGIC

T COM

030598 2/12

C. If the counter reaches zero before the

gate period is over, the temperature register, which is

also preset to the –55

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

C 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 tempera-

ture. The data is transmitted serially through the 3–wire

serial interface, LSB first. The DS1620 can measure

temperature over the range of –55

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 zero,

as illustrated in Table 1. After the MSB, the DS1620 will

output 0s.

increments. For Fahrenheit usage, a lookup table or con-

version factor must be used.

C to +125

C in 0.5

Note that temperature is represented in the DS1620 in

terms of a 1 / 2 ° C LSB, yielding the following 9–bit format:

MSB

LSB

XXXXX XX1 1 1 0 01 11 0

TEMPERATURE/DATA RELATIONSHIPS

Table 1

T = –25 ° C

TEMP

DIGITAL

OUTPUT

(Binary)

DIGITAL

OUTPUT

(Hex)

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 remain-

ing (COUNT_REMAIN) after the gate period has

ceased. By loading the value of the slope accumulator

into the count register (using the READ SLOPE com-

mand), this value may then be read, yielding the number

of counts per degree C (COUNT_PER_C) at that tem-

perature. The actual temperature may be then be calcu-

lated by the user using the following:

+125 ° C

0 11111010

00FA

+25

0 00110010

0032h

+ 1 /2 °

0 00000001

0001h

+0 ° C

0 00000000

0000h

– 1 / 2 ° C

1 11111111

01FFh

–25 ° C

1 11001110

01CEh

–55

1 10010010

0192h

Since data is transmitted over the 3–wire bus LSB first,

temperature data can be written to/read from the

TEMPERATURE = TEMP_READ – 0.25

(COUNT_PER_C – COUNT_REMAIN)

COUNT_PER_C

030598 3/12

This calculation is done inside the DS1620 to provide

0.5

Higher resolutions may be obtained by reading the tem-

perature, and truncating the 0.5

DS1620

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 as part of a closed loop system can be

used to activate a cooling system and to deactivate it

when the system temperature returns to tolerance.

falls below the value stored in the low temperature regis-

ter, 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 boundary has been met or

exceeded, or as part of a closed loop system, can be

used to activate a heating system and to deactivate it

when the system temperature returns to tolerance.

The T COM output goes high when the measured tem-

perature 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.

The T LOW output functions similarly to the T HIGH output.

When the DS1620’s measured temperature equals or

THERMOSTAT OUTPUT OPERATION Figure 3

T HIGH

T LOW

T COM

T (

030598 4/12

DS1620

OPERATION AND CONTROL

The DS1620 must have temperature settings resident in

the TH and TL registers for thermostatic operation. A

configuration/status register is also used to determine

the method of operation that the DS1620 will use in a

particular application, as well as indicating the status of

the temperature conversion operation. The configura-

tion register is defined as follows:

conversion upon reception of the Start

Convert T protocol. If 1SHOT is 0, the

DS1620 will continuously perform tem-

perature conversion. This bit is stored in

nonvolatile E 2 memory, capable of at least

50,000 writes. The DS1620 is shipped

with 1SHOT=0.

CONFIGURATION/STATUS REGISTER

For typical thermostat operation, the DS1620 will oper-

ate in continuous mode. However, for applications

where only one reading is needed at certain times, and

to conserve power, the one–shot mode may be used.

Note that the thermostat outputs (T HIGH , T LOW , T COM )

will remain in the state they were in after the last valid

temperature conversion cycle when operating in one–

shot mode.

DONE

THF

TLF

NVB

CPU 1SHOT

where

DONE =

Conversion Done bit. 1=conversion com-

plete, 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.

OPERATION IN STAND–ALONE MODE

In applications where the DS1620 is used as a simple

thermostat, no CPU is required. Since the temperature

limits are nonvolatile, the DS1620 can be programmed

prior to insertion in the system. In orde r to facilitate

operation without a CPU, the CLK/CONV pin (pin 2) can

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. Whether CPU=0 or 1, the 3–wire

port is active. Setting CPU=1 disables the stand–alone

mode.

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.

To use the CLK/CONV pin to in itiate conversions, RST

must b e 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 the n the DS1620 will return to an idle state. If CLK/

CONV is driven low and remains low, c ontinuous con-

versions will take place until CLK/CONV is br ought h igh

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.

NVB =

Nonvolatile Memory Busy Flag. 1=write to

an E 2 memory cell in progress. 0=nonvol-

atile 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 a cts a s 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 n ormal clock

in concert with DQ and RST. This bit is

stored in nonvolatile E 2 memory, capable

of at least 50,000 writes. The DS1620 is

shipped with CPU=0.

3–WIRE COMMUNICATIONS

The 3–w ire bus is comprised of three signals. These are

the RST (reset) signal, the CLK (clock) signal, and the

DQ (da ta) si gnal. All data transfers are i nitiated by driv-

ing the RST input high. Driving the RST input low termi-

nates communication. (See Figures 4 and 5.) 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. Data bits are output on the

1SHOT =

One–Shot Mode. If 1SHOT is 1, the

DS1620 will perform one temperature

030598 5/12

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