DS1621

5 of 16

102299

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 +

C

PER

COUNT

REMAIN

COUNT

C

PER

COUNT

_

_

)

_

_

_

(

−

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

THERMOSTAT OUTPUT OPERATION Figure 3

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:

where

DONE = Conversion Done bit. “1” = Conversion complete, “0” = Conversion in progress.

TL

TH

T (°C)

DONE

THF

TLF

NVB

1

0

POL

1SHOT