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

in the Operation and Control section of this datasheet.

Figure 3. THERMOSTAT OUTPUT OPERATION

DQ (Thermostat output, Active = High)

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

Bit5

Bit 4

Bit 3

Bit 2

Bit 1

LSb

DONE

THF

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.

TL

TH

T (°C)

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