LM75B Datasheet PDF - NXP

Part Number LM75B
Description Digital temperature sensor and thermal watchdog
Manufacturers NXP 
Logo NXP Logo 

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LM75B datasheet, circuit
Digital temperature sensor and thermal watchdog
Rev. 02 — 9 December 2008
Product data sheet
1. General description
The LM75B is a temperature-to-digital converter using an on-chip band gap temperature
sensor and Sigma-Delta A-to-D conversion technique with an overtemperature detection
output. The LM75B contains a number of data registers: Configuration register (Conf) to
store the device settings such as device operation mode, OS operation mode, OS polarity
and OS fault queue as described in Section 7 “Functional description”; temperature
register (Temp) to store the digital temp reading, and set-point registers (Tos and Thyst) to
store programmable overtemperature shutdown and hysteresis limits, that can be
communicated by a controller via the 2-wire serial I2C-bus interface. The device also
includes an open-drain output (OS) which becomes active when the temperature exceeds
the programmed limits. There are three selectable logic address pins so that eight devices
can be connected on the same bus without address conflict.
The LM75B can be configured for different operation conditions. It can be set in normal
mode to periodically monitor the ambient temperature, or in shutdown mode to minimize
power consumption. The OS output operates in either of two selectable modes:
OS comparator mode or OS interrupt mode. Its active state can be selected as either
HIGH or LOW. The fault queue that defines the number of consecutive faults in order to
activate the OS output is programmable as well as the set-point limits.
The temperature register always stores an 11-bit 2's complement data giving a
temperature resolution of 0.125 °C. This high temperature resolution is particularly useful
in applications of measuring precisely the thermal drift or runaway. When the LM75B is
accessed the conversion in process is not interrupted (i.e., the I2C-bus section is totally
independent of the Sigma-Delta converter section) and accessing the LM75B
continuously without waiting at least one conversion time between communications will
not prevent the device from updating the Temp register with a new conversion result. The
new conversion result will be available immediately after the Temp register is updated.
The LM75B powers up in the normal operation mode with the OS in comparator mode,
temperature threshold of 80 °C and hysteresis of 75 °C, so that it can be used as a
stand-alone thermostat with those pre-defined temperature set points.
2. Features
I Pin-for-pin replacement for industry standard LM75 and LM75A and offers improved
temperature resolution of 0.125 °C and specification of a single part over power supply
range from 2.8 V to 5.5 V
I I2C-bus interface with up to 8 devices on the same bus
I Power supply range from 2.8 V to 5.5 V
I Temperatures range from 55 °C to +125 °C

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LM75B equivalent
NXP Semiconductors
Digital temperature sensor and thermal watchdog
In OS comparator mode, the OS output behaves like a thermostat. It becomes active
when the Temp exceeds the Tth(ots), and is reset when the Temp drops below the Thys.
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 Tth(ots); then
it remains active indefinitely until being reset by a read of any register. Once the OS output
has been activated by crossing Tth(ots) and then reset, it can be activated again only when
the Temp drops below the Thys; then again, it remains active indefinitely until being reset
by a read of any register. The OS interrupt operation would be continued in this sequence:
Tth(ots) trip, Reset, Thys trip, Reset, Tth(ots) trip, Reset, Thys trip, Reset, etc. Putting the
device into the shutdown mode by setting the bit 0 of the configuration register also resets
the OS output.
In both cases, comparator mode and interrupt mode, the OS output is activated only if a
number of consecutive faults, defined by the device fault queue, has been met. The fault
queue is programmable and stored in the two bits, B3 and B4, of the Configuration
register. Also, the OS output active state is selectable as HIGH or LOW by setting
accordingly the configuration register bit B2.
At power-up, the device is put into normal operation mode, the Tth(ots) is set to 80 °C, the
Thys is set to 75 °C, the OS active state is selected LOW and the fault queue is equal to 1.
The temp reading data is not available until the first conversion is completed in about
100 ms.
The OS response to the temperature is illustrated in Figure 5.
OS reset
OS active
reading temperature limits
OS output in comparator mode
OS reset
OS active
(1) (1)
OS output in interrupt mode
(1) OS is reset by either reading register or putting the device in shutdown mode. It is assumed that
the fault queue is met at each Tth(ots) and Thys crossing point.
Fig 5. OS response to temperature
Product data sheet
Rev. 02 — 9 December 2008
© NXP B.V. 2008. All rights reserved.
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