Dallas Semiconductor DS1620S, DS1620 Datasheet
DS1620
Digital Thermometer and Thermostat
www.dalsemi.com
312
4
8
5
DQ
CLK/CONV
RST
GND
DD
T
HIGH
T
LOW
COM
312
4
8
5
DQ
CLK/CONV
RST
GND
DD
T
HIGH
T
LOW
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/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
V
7
6
T
DS1620S 8-Pin SOIC (208-miil)
See Mech Drawings Section
V
7
6
T
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
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.
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
RST - 3-Wire Reset Input
GND - Ground
T
T
T
V
HIGH
LOW
COM
DD
- High Temperature Trigger
- Low Temperature Trigger
- High/Low Combination Trigger
- Power Supply Voltage (3V - 5V)
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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 –55°C. If the counter reaches 0
before the gate period is over, the temperature register, which is also preset to the –55°C value, is
incremented, indicating that the temperature is higher than –55°C.
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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TEMPERATURE MEASURING CIRCUITRY Figure 2
LSB
SLOPE ACCUMULATOR
PRESET COMPARE
DS1620
LOW TEMPERATURE
COEFFICIENT OSCILLATOR
HIGH TEMPERATURE
COEFFICIENT OSCILLATOR
COUNTER PRESET
INC
=0
COUNTER
STOP
=0
TEMPERATURE REGISTER
SET/CLEAR
This calculation is done inside the DS1620 to provide 0.5°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 temperature. 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.
TEMPERATURE/DATA RELATIONSHIPS Table 1
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
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
DIGITAL OUTPUT
(Hex)
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DS1620
XXXXXXX
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 ½°C LSB, yielding the following 9–bit
format:
MSB
LSB
1
T = -25°C
1 1 0 0 11 1 0
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 +
IN)COUNT_REMA-_C(COUNT_PER
CCOUNT_PER_
DETAILED PIN DESCRIPTION Table 2
PIN SYMBOL DESCRIPTION
1 DQ Data Input/Output pin for 3-wire communication port.
2
3
CLK/CONV
RST
4 GND
5 T
6 T
7 T
8 V
COM
LOW
HIGH
DD
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.
Reset input pin for 3-wire communication port.
Ground pin.
High/Low Combination Trigger. Goes high when temperature exceeds TH;
will reset to low when temperature falls below TL.
Low Temperature Trigger. Goes high when temperature falls below TL.
High Temperature Trigger. Goes high when temperature exceeds TH.
Supply Voltage. 2.7V – 5.5V input power pin.
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
, 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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