Datasheet

Operation—Measuring Temperature
The DS1631, DS1631A, and DS1731 measure tempera-
ture using bandgap-based temperature sensors. A delta-
sigma analog-to-digital converter (ADC) converts the
measured temperature to a 9-, 10-, 11-, or 12-bit (user-
selectable) digital value that is calibrated in °C; for °F
applications a lookup table or conversion routine must be
used. Throughout this data sheet, the term “conversion” is
used to refer to the entire temperature measurement and
ADC sequence.
The DS1631 and DS1731 always power-up in a low-pow-
er idle state, and the Start Convert T command must be
used to initiate conversions. The DS1631A begins conver-
sions automatically at power-up in the mode determined
by the configuration register’s 1SHOT bit.
The DS1631, DS1631A, and DS1731 can be programmed
to perform continuous consecutive conversions (continu-
ous-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 Configuration Register sec-
tion of this data sheet. In continuous-conversion mode,
the DS1631A begins performing continuous conversions
immediately at power-up, and the DS1631 and DS1731
begin continuous conversions after a Start Convert T
command is issued. For all three devices, consecu-
tive 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.
In one-shot mode the DS1631A performs a single con-
version at power-up, and the DS1631 and DS1731
perform a single temperature conversion when a Start
Convert T command is issued. For all three devices,
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.
The resolution of the output digital temperature data is
user-configurable to 9, 10, 11, or 12 bits, corresponding
to temperature increments of 0.5°C, 0.25°C, 0.125°C, and
0.0625°C, respectively. The default resolution at power-
up is 12 bits, and it can be changed through the R0 and
R1 bits in the configuration register. Note that the conver-
sion time doubles for each additional bit of resolution.
After each conversion, the digital temperature is stored
as a 16-bit two’s complement number in the two-byte
temperature register as shown in Figure 4. The sign bit
(S) indicates if the temperature is positive or negative:
for positive numbers S = 0 and for negative numbers
S = 1. The Read Temperature command provides user
access to the temperature register. Bits 3 through 0 of
the temperature register are hardwired to 0. When the
device is configured for 12-bit resolution, the 12 MSbs
(bits 15 through 4) of the temperature register contain
temperature data. For 11 bit resolution, the 11 MSbs (bits
15 through 5) of the temperature register contain data,
and bit 4 is 0. Likewise, for 10-bit resolution, the 10 MSbs
(bits 15 through 6) contain data, and for 9-bit the 9 MSbs
(bits 15 through 7) contain data, and all unused LSbs con-
tain 0s. Table 4 gives examples of 12-bit resolution output
data and the corresponding temperatures.
Table 4. 12-Bit Resolution Temperature/
Data Relationship
TEMPERATURE
(°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL
OUTPUT (HEX)
[phone] 0000 7D00h
+25.0625 0001 1001 0001 0000 1910h
+10.125 0000 1010 0010 0000 0A20h
+0.5 0000 0000 1000 0000 0080h
0 0000 0000 0000 0000 0000h
-0.5 1111 1111 1000 0000 FF80h
-10.125 1111 0101 1110 0000 F5E0h
-25.0625 1110 0110 1111 0000 E6F0h
-55 1100 1001 0000 0000 C900h
Figure 4. Temperature, T
H
, And T
L
Register Format
BIT 15 BIT 14 BIT 13 BIT 12 BIT 11 BIT 10 BIT 9 BIT 8
MS BYTE S 2
6
2
5
2
4
2
3
2
2
2
1
2
0
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
LS BYTE 2
-1
2
-2
2
-3
2
-4
0 0 0 0
DS1631/DS1631A/
DS1731
High-Precision Digital
Thermometer and Thermostat
www.maximintegrated.com
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