Datasheet
LM75B All information provided in this document is subject to legal disclaimers. © NXP B.V. 2015. All rights reserved.
Product data sheet Rev. 6.1 — 6 February 2015 10 of 37
NXP Semiconductors
LM75B
Digital temperature sensor and thermal watchdog
For 9-bit Temp data application in replacing the industry standard LM75, just use only
9 MSB bits of the two bytes and disregard 7 LSB of the LSByte. The 9-bit Temp data with
0.5 C resolution of the LM75B is defined exactly in the same way as for the standard
LM75 and it is here similar to the Tos and Thyst registers.
The only MSByte of the temperature can also be read with the use of a one-byte reading
command. Then the temperature resolution will be 1.00 C instead.
7.4.4 Overtemperature shutdown threshold (Tos) and hysteresis (Thyst) registers
These two registers, are write/read registers, and also called set-point registers. They are
used to store the user-defined temperature limits, called overtemperature shutdown
threshold (T
th(ots)
) and hysteresis temperature (T
hys
), for the device watchdog operation.
At the end of each conversion the Temp data will be compared with the data stored in
these two registers in order to set the state of the device OS output; see Section 7.1
.
Each of the set-point registers contains two 8-bit data bytes consisting of one MSByte and
one LSByte the same as register Temp. However, only 9 bits of the two bytes are used to
store the set-point data in two’s complement format with the resolution of 0.5 C. Table 11
and Table 12
show the bit arrangement of the Tos data and Thyst data in the data bytes.
Notice that because only 9-bit data are used in the set-point registers, the device uses
only the 9 MSB of the Temp data for data comparison.
When a set-point register is read, all 16 bits are provided to the bus and must be collected
by the controller to complete the bus operation. However, only the 9 most significant bits
should be used and the 7 LSB of the LSByte are equal to zero and should be ignored.
Table 13
shows examples of the limit data and value.
000 0000 0000 000 0 0.000 C
111 1111 1111 7FF 1 0.125 C
111 0011 1000 738 200 25.000 C
110 0100 1001 649 439 54.875 C
110 0100 1000 648 440 55.000 C
Table 10. Temp register value
…continued
11-bit binary
(two’s complement)
Hexadecimal value Decimal value Value
Table 11. Tos register
MSByte LSByte
7654321076543210
D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X X X X
Table 12. Thyst register
MSByte LSByte
7654321076543210
D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X X X X