Datasheet
MAX31725/MAX31726
±0.5°C Local Temperature Sensors
11Maxim Integrated
Table 3. Temperature, T
HYST
, and T
OS
Register Definition
Figure 4. I
2
C-Compatible Timing Diagram (Read)
Perform a read operation by issuing the slave address
byte (write), pointer byte, repeat START, another slave
address byte (read), and then reading the data byte.
After 2 data bytes the pointer register auto increments
and, if pointing to a valid address, additional data can be
read. See Figure 4.
Temperature Registers
Temperature data is stored in the temperature, T
OS
set
point, and T
HYST
set point registers. The temperature
data format is 16 bits, two’s complement, and the register
is read out in 2 bytes: an upper byte and a lower byte.
Bits D[15:0] contains the temperature data, with the LSB
representing 0.00390625NC and the MSB representing
the sign bit; see Table 3. The MSB is transmitted first.
In addition to the normal two’s complement temperature
data format, the MAX31725 and MAX31726 offer an
optional extended data format that allows temperatures
equal to or greater than +128NC to be read. In the
extended format, selected by bit 5 of the configuration
register, the measured temperature is the value in the
temperature register plus 64NC, as shown in Table 4.
UPPER BYTE LOWER BYTE
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
S
MSB
64
N
C
32NC 16NC 8NC 4NC 2NC 1NC 0.5NC 0.25NC 0.125NC 0.0625NC 0.03125NC 0.015625NC 0.0078125NC 0.00390625NC
2
6
2
5
2
4
2
3
2
2
2
1
2
0
2
-1
2
-2
2
-3
2
-4
2
-5
2
-6
2
-7
2
-8
ADDRESS BYTE
ADDRESS
BYTE
(b) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FOR 2-BYTE REGISTER SUCH AS TEMPERATURE, T
OS
, AND T
HYST
.
POINTER BYTE
MOST SIGNIFICANT
DATA BYTE
LEAST SIGNIFICANT
DATA BYTE
ACK BY
MAX31725/
MAX31726
ACK BY
MAX31725/
MAX31726
ACK BY
MASTER
ACK BY
MAX31725/
MAX31726
START
BY
MASTER
1
10 000000D3*D4*D5* D2* D1* D1 D0
199
REPEAT
START
BY
MASTER
STOP
COND BY
MASTER
NO
ACK BY
MASTER
119 19 9
R/W
10 D3*D4* D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0D5* D2* D1* R/W
ADDRESS
BYTE
(a) TYPICAL POINTER SET FOLLOWED BY IMMEDIATE READ FROM CONFIGURATION REGISTER.
POINTER
BYTE
ADDRESS
BYTE
DATA
BYTE
ACK BY
MAX31725/
MAX31726
ACK BY
MAX31725/
MAX31726
START
BY
MASTER
REPEAT
START
BY
MASTER
NO
ACK BY
MASTER
STOP
COND BY
MASTER
ACK BY
MAX31725/
MAX31726
10 D3*D4*D5* D2* D1*
R/W 00D1D0 D0D1D2D3D4D5D6D7000001D3*D4*D5* D2* D1* R/W
11 1199
99
*SEE TABLE 1A.