LM75B
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: Con?guration 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 I
2
C-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 con?ict.
The LM75B can be con?gured 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 de?nes 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 I
2
C-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-de?ned 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 speci?cation of a single part over power supply
range from 2.8 V to 5.5 V
I
I
2
C-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