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)

+125

0111 1101 0000 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

BIT 15

BIT 14

BIT 13

BIT 12

BIT 11

BIT 10

BIT 9

BIT 8

MS BYTE

S

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

LS BYTE

0

0

0

0

DS1631/DS1631A/

DS1731

High-Precision Digital

Thermometer and Thermostat

www.maximintegrated.com

Maxim Integrated │ 6