L9945 datasheet(32/151 Pages) STMICROELECTRONICS

32 / 151 page

5.5.4

H-bridge disabling

When DIS/NDIS is asserted the H-bridge is disabled and all the pre-drivers are actively turned off. The same

behavior is observed when HiZ or NRES is asserted.

Table 21. H-bridge state for different DIS/NDIS and NRES

NRES

HiZ

HBx_config

DIS

NDIS

H-bridge state

All 4 MOSFET actively OFF

Normal operation

All 4 MOSFET actively OFF

HBx_config must not be changed while H-Bridge is operating.

5.5.5

Overcurrent detection strategies for H-Bridge

The over current detection can be performed either by measuring the voltage drop on external shunt resistors or

through the Drain to Source Measurement of each transistor (DSM). Each transistor of the H-Bridge can detect

overcurrent independently. If an OC event occurs on a channel, the four devices will be actively shut-off and H-

Bridge outputs will be three-stated. Diagnostic latches have always to be cleared before re-engaging the H-Bridge

after an overcurrent detection. Different scenarios for OC detection are possible:

•

OC detection through one shunt resistor mounted on the low-side between SNGPx and PGNDxx pins, as

shown in Figure 16. DSM used for OC detection on the HS transistors.

–

To avoid inhomogeneous OC protection over the H-Bridge, OC threshold programmed for HS via DSM

must be adapted to the ones programmed on the LS via shunt sensing. OC threshold adaption must

account for the RDSon of the HS devices.

•

OC detection through two shunt resistors. The first mounted on the low-side between SNGPx and PGNDxx

pins, the second mounted on the high-side between GNSPx (PMOS)/DRNx (NMOS) and BATTxx pins (see

Figure 16).

–

To avoid inhomogeneous OC threshold for the H-Bridge, the two shunt resistors must be equal and the

four OC thresholds must hold the same value.

•

OC detection through DSM (see Figure 16)

–

In case the 4 MOSFETs are equal, the 4 OC thresholds must be equal;

–

In case the 2 FETs used on high-side are different from the ones on low-side, a different value for OC

threshold must be specified for the HS pair. OC threshold adaption must account for the RDSon of the

HS devices.

L9945

H-Bridge

DS12275 - Rev 8

page 32/151

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