DS1621 Datasheet, PDF (5/16 Pages) Dallas Semiconductor – Digital Thermometer and Thermostat

DS1621
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.
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
Bit 6
DONE THF
Bit5
Bit 4 Bit 3 Bit 2 Bit 1
LSb
TLF NVB X
X
POL 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 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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