L6758ATR datasheet(30/42 Pages) STMICROELECTRONICS

30 / 42 page

Single NTC thermal monitor and compensation

L6758A

30/42

DocID023298 Rev 2

Single NTC thermal monitor and compensation

The L6758A features single NTC for thermal sensing for both thermal monitoring and

compensation. The feature is per section, i.e. it is required to have one NTC per section

which drives both thermal monitoring and thermal compensation. The thermal monitor

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 the performance.

8.1

Thermal monitor and VR_HOT

The diagram for the thermal monitor is reported in

Figure 8. 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 and STM pins.

The recommended NTC is NTHS0805N02N6801 (or equivalent with

25/75

=3500 +/-10%)

for accurate temperature sensing and thermal compensation. Different NTC may be used:

to reach the required 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 / STM pins is internally converted and then used to fill in the

temperature zone register of the related section. When the temperature observed exceeds

TMAX (programmed via pinstrapping), the L6758A 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 8. Thermal monitor connections (also applies to STM pin)

AM11141v1

VCC5

VR_HOT

Temp. Zone

L6758ATR Datasheet(PDF) 30 Page - STMicroelectronics