L6759D datasheet(32/51 Pages) STMICROELECTRONICS

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Single NTC thermal monitor and compensation

L6759D

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Doc ID 023240 Rev 1

Single NTC thermal monitor and compensation

The L6759D features single NTC for thermal sensing for both thermal monitoring and

compensation. Thermal monitoring consists of monitoring the converter temperature

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

temperature zone register fill. Thermal compensation consists of compensating the inductor

DCR derating with temperature, so preventing drifts in any variable correlated to the DCR:

voltage positioning, overcurrent, Imon, current reporting. Both functions share the same

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

performance.

8.1

Thermal monitor and VR_HOT

The diagram for the 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, so reducing the voltage

observable at the TM pin.

The recommended NTC is NTHS0805N02N6801HE for accurate temperature sensing and

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

temperature reporting, a 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 pin is internally converted and then used to fill in the

temperature zone register. When the temperature observed exceeds TMAX (programmed

via PMBus, the default value is 110 °C), the L6759D asserts VR_HOT (active low - as long

as the overtemperature event lasts) and the ALERT# line (until reset by the GetReg

command on the status register).

Figure 11.

Thermal monitor connections

VCC5

VR_HOT

Temp. Zone

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