L9945 datasheet(129/151 Pages) STMICROELECTRONICS

129 / 151 page

Symbol

Parameter

Condition

Min. Typ.

Max. Unit

tFIL_ON

OC deglitch filter time

0.6

µs

tOC

OC Detection filter time

µs

6.3.6

Temperature compensation for OC threshold

L9945 offers the possibility to compensate the OC threshold against temperature variations. Such feature can be

enabled independently on each channel.

The device is able to monitor the internal junction temperature Tj through on board Temperature ADC. Given the

estimated temperature variation between L9945 junction and the external FET junction

Eq. (4): Estimated temperature variation for the compensation algorithm

ΔT=TjFET−Tj

(4)

An internal algorithm measures Tj and is able to compensate VOC against RDSon variations induced by TjFET.

The latter can be estimated according to the given application and operating scenario.

Temperature compensation can be enabled by programming the OC_Temp_comp_xx bit according to the

following table:

Table 42. Temperature compensation

OC_Temp_comp_xx

Function

Temperature compensation deactivated

Temperature compensation active for estimated ∆T < 60 °C. TCF is saturated at '1' for

Tj ≥ Tj_SAT = 83 °C.

Temperature compensation active for estimated ∆T < 40 °C. TCF is saturated at '1' for

Tj ≥ Tj_SAT = 96 °C.

Temperature compensation active for estimated ∆T < 25 °C. TCF is saturated at '1' for

Tj ≥ Tj_SAT = 108 °C.

In case temperature compensation is enabled, the overcurrent threshold must be programmed according to Eq.

(3), where ROC is the RDSon of the external FET evaluated for TjFET = 150 °C.

The internal algorithm compensates the OC threshold based on a multiplicative factor:

Eq. (5): Temperature Compensation Factor (TCF)

VOC_comp=TCF×VOC

(5)

TCF = 1 when Tj ≥ Tj_SAT, and it's decremented with a constant slope of 0.38 %/°C for Tj < Tj_SAT.

L9945

ON state diagnostics

DS12275 - Rev 8

page 129/151

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