L9945 datasheet(130/151 Pages) STMICROELECTRONICS

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Figure 32. TCF vs. Tj

GADG2212171232PS

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.1

Tj [°C]

TCF (Δ = 25°C)

TCF (Δ = 40°C)

TCF (Δ = 60°C)

Note:

This feature is recommended only in case of DSM, because the compensation algorithm is based on RDSon

variations. The external FET must have a characteristic RDSon vs. TjFET that matches the 0.38 %/°C slope. In

case of shunt measurement, the algorithm may show performances worse than the uncompensated strategy.

6.3.7

Battery compensation for OC threshold

L9945 offers the possibility to compensate the OC threshold against battery variations. This feature can be

enabled when driving a resistive output load RL, and helps preventing the load resistance from dropping below a

minimum threshold RLmin. Given Eq. (3), the IOC can be evaluated as the current flowing when the battery is at its

maximum operating value (18 V for passenger vehicles or 36 V for commercial vehicles) and the load resistance

assumes its minimum allowed value RLmin:

Eq. (6): Overcurrent detection in case of resistive load

IOC≅VBATTmax

RLmin VOC=ROC×VBATTmax

RLmin

(6)

Eq. (6) assumes that RL >> ROC. The sensing resistance ROC can be either the shunt resistor or the RDSon.

Referring to Figure 34 and Figure 35, the device measures:

Eq. (7): Overcurrent sensing in case of resistive load

VSENSE=ROC×ILOAD=ROC×VBATTRL

(7)

The device is able to monitor the battery voltage on the VPS pin through the on board VPS ADC. This information

can be used to compensate the VOC with respect to VBATT variations. Therefore, the OC detection occurs only

when VSENSE = VOC due to a RL variation.

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

Eq. (8): Battery Compensation Factor (BCF)

VOCcomp=BCF×VOC

(8)

The battery compensation feature can be activated independently on each channel by programming the

OC_Batt_comp_xx bit. Two different BCF have been implemented for Passenger Vehicle (PV) and Commercial

Vehicle (CV) applications. The BCF can be selected by programming the Batt_fact_config bit (refer to

Figure 33).

L9945

ON state diagnostics

DS12275 - Rev 8

page 130/151

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