LM75B_2

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 02 — 9 December 2008

16 of 29

NXP Semiconductors

LM75B

Digital temperature sensor and thermal watchdog

[5]

The LM75B performs the temperature-to-data conversions with a much higher speed than the LM75A. While the LM75A takes almost

two parts. A shorter conversion time is applied to significantly reduce the device’s average power dissipation. During each conversion

period, when the conversion is completed, the LM75B becomes idled and the power is reduced, resulting in a lesser average power

consumption.

8.3 Temperature accuracy

Because the local channel of the temperature sensor measures its own die temperature

that is transferred from its body, the temperature of the device body must be stabilized and

saturated for it to provide the stable readings. Because the LM75B operates a a low power

level, the thermal gradient of the device package has a minor effect on the measurement.

The accuracy of the measurement is more dependent upon the definition of the

environment temperature, which is affected by different factors: the printed-circuit board

on which the device is mounted; the air flow contacting the device body (if the ambient air

temperature and the printed-circuit board temperature are much different, then the

measurement may not be stable because of the different thermal paths between the die

and the environment). The stabilized temperature liquid of a thermal bath will provide the

best temperature environment when the device is completely dipped into it. A thermal

probe with the device mounted inside a sealed-end metal tube located in consistent

temperature air also provides a good method of temperature measurement.

8.4 Noise effect

The LM75B device design includes the implementation of basic features for a good noise

immunity:

500 mV minimum;

ESD protection on the address, OS, SCL and SDA pins it to ground. The latch-back

based device breakdown voltage of address/OS is typically 11 V and SCL/SDA is

typically 9.5 V at any supply voltage but will vary over process and temperature. Since

operation if the LM75B is de-powered.

However, good layout practices and extra noise filters are recommended when the device

is used in a very noisy environment:

characteristics.