lm75adp NXP Semiconductors, lm75adp Datasheet - Page 4

• Manufacturer Part Number: lm75adp
• Description: Digital Temperature Sensor And Thermal Watchdog
• Manufacturer: NXP Semiconductors

NXP Semiconductors
7. Functional description
LM75A_4
Product data sheet
7.1 General operation
Table 3.
The LM75A uses the on-chip band gap sensor to measure the device temperature with
the resolution of 0.125 C and stores the 11-bit 2's complement digital data, resulted from
11-bit A-to-D conversion, into the device Temp register. This Temp register can be read at
any time by a controller on the I
conversion in progress during the read operation.
The device can be set to operate in either mode: normal or shutdown. In normal operation
mode, the temp-to-digital conversion is executed every 100 ms and the Temp register is
updated at the end of each conversion. In shutdown mode, the device becomes idle, data
conversion is disabled and the Temp register holds the latest result; however, the device
I
device operation mode is controllable by programming bit B0 of the configuration register.
The temperature conversion is initiated when the device is powered-up or put back into
normal mode from shutdown.
In addition, at the end of each conversion in normal mode, the temperature data (or Temp)
in the Temp register is automatically compared with the overtemperature shutdown
threshold data (or Tos) stored in the Tos register, and the hysteresis data (or Thyst) stored
in the Thyst register, in order to set the state of the device OS output accordingly. The
device Tos and Thyst registers are write/read capable, and both operate with 9-bit
2's complement digital data. To match with this 9-bit operation, the Temp register uses
only the 9 MSB bits of its 11-bit data for the comparison.
The way that the OS output responds to the comparison operation depends upon the OS
operation mode selected by configuration bit B1, and the user-defined fault queue defined
by configuration bits B3 and B4.
In OS comparator mode, the OS output behaves like a thermostat. It becomes active
when the Temp exceeds the T
Reading the device registers or putting the device into shutdown does not change the
state of the OS output. The OS output in this case can be used to control cooling fans or
thermal switches.
In OS interrupt mode, the OS output is used for thermal interruption. When the device is
powered-up, the OS output is first activated only when the Temp exceeds the T
remains active indefinitely until being reset by a read of any register. Once the OS output
has been activated by crossing T
Temp drops below the T
read of any register. The OS interrupt operation would be continued in this sequence:
T
Symbol
A1
A0
V
2
os
C-bus interface is still active and register write/read operation can be performed. The
CC
trip, Reset, T
Pin description
hyst
Pin
6
7
8
trip, Reset, T
Rev. 04 — 10 July 2007
hyst
…continued
; then again, it remains active indefinitely until being reset by a
Description
Digital input. User-defined address bit 1.
Digital input. User-defined address bit 0.
Power supply.
os
2
, and is reset when the Temp drops below the T
C-bus. Reading temperature data does not affect the
os
os
and then reset, it can be activated again only when the
trip, Reset, T
Digital temperature sensor and thermal watchdog
hyst
trip, Reset, etc.
© NXP B.V. 2007. All rights reserved.
LM75A
os
hyst
; then it
.
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