L6718 datasheet(59/71 Pages) STMICROELECTRONICS

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L6718

Single NTC thermal monitor and compensation

The L6718 features single NTC for thermal sensing for both thermal monitoring and

compensation. The thermal monitor consists in 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 and 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.

TM and TCOMP are pins used for the multi-rail thermal compensation and monitoring while

STM and STCOMP are used for single-rail, as a consequence every consideration for TM

and TCOMP in Section 10.2 and Section 10.3 can be used for STM and STCOMP for the

single-rail.

10.1

Thermal monitor and VR_HOT

The diagram for the thermal monitor is shown in Figure 13. 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 pin.

Recommended NTC is NTHS0805N02N6801 (or equivalent with

β25/75 = 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 characteristics with those 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 pinstrapping), the L6718 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

Figure 13. Thermal monitor connections

VCC5

VR_HOT

Temp. Zone

AM12887v1

L6718 Datasheet(PDF) 59 Page - STMicroelectronics