DS1621
Digital Thermometer and
BENEFITS AND FEATURES
Simply Adds Temperature Monitoring and
Control to Any System
o
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
o
Temperature is Read as a 9-Bit Value (2-
Byte Transfer)
o
Converts Temperature to Digital Word in
Less than 1s
o
Thermostatic Settings are User Definable
And Nonvolatile
Can Be Used in a Wide Variety of
Applications
o
Power Supply Range (2.7V to 5.5V)
o
Data is Read From/Written Via a 2-Wire
Serial Interface (Open Drain I/O Lines)
Saves Space
o
Temperature Measurements Require No
External Components
o
8-pin DIP or SO package (208-mil)
Packages
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Thermostatic Controls
Industrial Systems
Consumer Products
Thermometers
PIN ASSIGNMENT
SDA
SCL
T
OUT
GND
1
2
3
4
8
7
6
5
V
DD
A
0
A
1
A
2
DS1621S 8-PIN SO (150mil)
DS1621V 8-PIN SO (208mil)
SDA
SCL
T
OUT
GND
1
2
3
4
8
7
6
5
V
DD
A
0
A
1
A
2
DS1621 8-PIN DIP (300mil)
APPLICATIONS
SDA
SCL
GND
T
OUT
A0
A1
A2
V
DD
PIN DESCRIPTION
- 2-Wire Serial Data Input/Output
- 2-Wire Serial Clock
- Ground
- Thermostat Output Signal
- Chip Address Input
- Chip Address Input
- Chip Address Input
- Power Supply Voltage
The DS1621 Digital Thermometer and Thermostat provides 9-bit temperature readings, which indicate
the temperature of the device. The thermal alarm output, T
OUT
,
is active when the temperature of the
device exceeds a user-defined temperature TH. The output remains active until the temperature drops
below user defined temperature TL, allowing for any hysteresis necessary.
User-defined temperature settings are stored in nonvolatile memory so parts may be programmed prior to
insertion in a system. Temperature settings and temperature readings are all communicated to/from the
DS1621 over a simple 2-wire serial interface.
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19-7540; Rev 4; 3/15
DESCRIPTION
ORDERING INFORMATION
ORDERING
NUMBER
DS1621
DS1621+
DS1621S
DS1621S+
DS1621S/T&R
DS1621S+T&R
DS1621V
DS1621V+
DS1621V/T&R
DS1621V+T&R
DS1621
PACKAGE
MARKING
DS1621
DS1621 (See Note)
DS1621
DS1621 (See Note)
DS1621
DS1621 (See Note)
DS1621V
DS1621V (See Note)
DS1621V
DS1621V (See Note)
DESCRIPTION
DS1621 in 300 mil DIP
DS1621 in Lead-Free 300 mil DIP
DS1621 in 150 mil SOIC
DS1621 in Lead-Free 150 mil SOIC
DS1621 in 150 mil SO, 2500 Piece Tape-and-Reel
DS1621 in Lead-Free 150 mil SO, 2500 Piece Tape-and-Reel
DS1621 in 208 mil SOIC
DS1621 in Lead-Free 208 mil SOIC
DS1621 in 208 mil SO, 2500 Piece Tape-and-Reel
DS1621 in Lead-Free 208 mil SO, 2500 Piece Tape-and-Reel
Note: A “+” symbol will also be marked on the package near the Pin 1 indicator.
Table 1. DETAILED PIN DESCRIPTION
PIN
1
2
3
4
5
6
7
8
SYMBOL
SDA
SCL
T
OUT
GND
A2
A1
A0
V
DD
DESCRIPTION
Data input/output pin for 2-wire serial communication port.
Clock input/output pin for 2-wire serial communication port.
Thermostat output. Active when temperature exceeds TH; will reset when
temperature falls below TL.
Ground pin.
Address input pin.
Address input pin.
Address input pin.
Supply voltage input power pin. (2.7V to 5.5V)
OPERATION
Measuring Temperature
A block diagram of the DS1621 is shown in Figure 1.
The DS1621 measures temperature using a bandgap-based temperature sensor. A delta-sigma analog-to-
digital converter (ADC) converts the measured temperature to a digital value that is calibrated in °C; for
°F applications, a lookup table or conversion routine must be used.
The temperature reading is provided in a 9-bit, two’s complement reading by issuing the READ
TEMPERATURE command. Table 2 describes the exact relationship of output data to measured
temperature. The data is transmitted through the 2-wire serial interface, MSB first. The DS1621 can
measure temperature over the range of -55°C to +125°C in 0.5°C increments.
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Figure 1. DS1621 FUNCTIONAL BLOCK DIAGRAM
STATUS REGISTER &
CONTROL LOGIC
DS1621
SCL
ADDRESS
AND
I/O CONTROL
TEMPERATURE SENSOR
SDA
HIGH TEMP TRIGGER, TH
A0
A1
A2
LOW TEMP TRIGGER, TL
DIGITAL COMPARATOR/LOGIC
T
OUT
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DS1621
Table 2. TEMPERATURE/DATA RELATIONSHIPS
TEMPERATURE
+125°C
+25°C
+½°C
+0°C
-½°C
-25°C
-55°C
DIGITAL OUTPUT
(Binary)
01111101 00000000
00011001 00000000
00000000 10000000
00000000 00000000
11111111 10000000
11100111 00000000
11001001 00000000
DIGITAL OUTPUT
(Hex)
7D00h
1900h
0080h
0000h
FF80h
E700h
C900h
Since data is transmitted over the 2-wire bus MSB first, temperature data may be written to/read from the
DS1621 as either a single byte (with temperature resolution of 1°C) or as two bytes. The second byte
would contain the value of the least significant (0.5°C) bit of the temperature reading as shown in Table
1. Note that the remaining 7 bits of this byte are set to all "0"s.
Temperature is represented in the DS1621 in terms of a ½°C LSB, yielding the following 9-bit format:
Figure 2. TEMPERATURE, TH, and TL FORMAT
MSB
1
1
1
0
0
1
1
1
LSB
0
0
0
0
0
0
0
0
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. A Read Counter command should be issued to yield the
COUNT_REMAIN value.
The Read Slope command should then be issued to obtain the
COUNT_PER_C value. The higher resolution temperature may be then be calculated by the user using
the following:
TEMPERATURE=TEMP_READ-0.25 +
(
COUNT
_
PER
_
C
−
COUNT
_
REMAIN
)
COUNT
_
PER
_
C
The DS1621 always powers up in a low power idle state, and the Start Convert T command must be used
to initiate conversions.
The DS1621 can be programmed to perform continuous consecutive conversions (continuous-conversion
mode) or to perform single conversions on command (one-shot mode). The conversion mode is
programmed through the 1SHOT bit in the configuration register as explained in the
Operation and
Control
section of this datasheet. In continuous conversion mode, the DS1621 begins continuous
conversions after a Start Convert T command is issued. Consecutive conversions continue to be
performed until a Stop Convert T command is issued, at which time the device goes into a low-power idle
state. Continuous conversions can be restarted at any time using the Start Convert T command.
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In one-shot mode, the DS1621 performs a single temperature conversion when a Start Convert T
command is issued. When the conversion is complete, the device enters a low-power idle state and
remains in that state until a single temperature conversion is again initiated by a Start Convert T
command.
Thermostat Control
In its operating mode, the DS1621 functions as a thermostat with programmable hysteresis as shown in
Figure 3. The thermostat output updates as soon as a temperature conversion is complete.
DS1621
When the DS1621’s temperature meets or exceeds the value stored in the high temperature trip register
(TH), the output becomes active and will stay active until the temperature falls below the temperature
stored in the low temperature trigger register (TL). In this way, any amount of hysteresis may be
obtained.
The active state for the output is programmable by the user so that an active state may either be a logic
"1" (V
DD
) or a logic "0" (0V). This is done using the POL bit in the configuration reagister as explained
in the
Operation and Control
section of this datasheet.
Figure 3. THERMOSTAT OUTPUT OPERATION
DQ (Thermostat output, Active = High)
TL
TH
T (°C)
OPERATION AND CONTROL
The DS1621 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 DS1621 will
use in a particular application, as well as indicating the status of the temperature conversion operation.
The configuration register is defined as follows:
MSb
DONE
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 removing power
from the device. This feature provides a method of determining if the DS1621 has ever been subjected to
temperatures above TH while power has been applied.
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Bit 6
THF
Bit5
TLF
Bit 4
NVB
Bit 3
X
Bit 2
X
Bit 1
POL
LSb
1SHOT
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