L6751B datasheet(39/58 Pages) STMICROELECTRONICS

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L6751B

Single NTC thermal monitor and compensation

Doc ID 024028 Rev 1

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Single NTC thermal monitor and compensation

The L6751B features single NTC for thermal sensing for both thermal monitoring and

compensation. Thermal monitor consists in monitoring the converter temperature eventually

reporting alarm by asserting the VR_HOT signal. This is the base for the temperature

reporting. Thermal compensation consists in compensating the inductor DCR derating with

temperature, so preventing drifts in any variable correlated to the DCR: voltage positioning,

overcurrent (ILIM), IMON, current reporting. Both the functions share the same thermal

sensor (NTC) to optimize the overall application cost without compromising performance.

Thermal monitor is featured for both single-phase and multi-phase sections.

8.1

Thermal monitor and VR_HOT

The diagram for thermal monitor is reported in Figure 11. NTC should be placed close to the

power stage hot-spot in order to sense the regulator temperature. As the temperature of the

power stage increases, the NTC resistive value decreases, therefore reducing the voltage

observable at the TM/STM pin.

Recommended NTC is NTHS0805N02N6801HE for accurate temperature sensing and

thermal compensation. Different NTC may be used: to reach the requested accuracy in

temperature reporting, proper resistive network must be used in order to match the resulting

characteristic with the one coming from the recommended NTC.

The voltage observed at the TM/STM pin is internally converted and then used for the

temperature reporting. When the temperature observed on one of the two thermal sensors

exceeds TMAX (programmed via pinstrapping), the L6751B asserts VR_HOT (active low -

as long as the overtemperature event lasts).

Figure 11.

Thermal monitor connections

8.2

Thermal compensation

The L6751B supports DCR sensing for output voltage positioning: the same current

information used for voltage positioning is used to define the overcurrent protection and the

current reporting. Having imprecise and temperature-dependant information leads to

violation of the specification and misleading information: positive thermal coefficient specific

from DCR needs to be compensated to get stable behavior of the converter as temperature

VCC5

VR_HOT

Temp. zone

AM14843v1

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