1. General description
The LM75A is a temperature-to-digital converter using an on-chip band gap temperature
sensor and Sigma-delta A-to-D conversion technique. The device is also a thermal
detector providing an overtemperature detection output. The LM75A 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 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 conflict.
The LM75A 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.
The device is powered-up in 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
n Pin-for-pin replacement for industry standard LM75 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
n Small 8-pin package types: SO8 and TSSOP8
n I
2
C-bus interface with up to 8 devices on the same bus
n Power supply range from 2.8 V to 5.5 V
n Temperatures range from −55 °C to +125 °C
n 11-bit ADC that offers a temperature resolution of 0.125 °C
LM75A
Digital temperature sensor and thermal watchdog
Rev. 04 — 10 July 2007 Product data sheet
