L99DZ320 datasheet(73/146 Pages) STMICROELECTRONICS

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3.27

Short-circuit detection/ drain-source monitoring

The drain-source voltage of each activated external Power MOSFET of the H-bridge is monitored by comparators

to detect shorts to ground or battery. If the voltage drop over the external Power MOSFET exceeds the threshold

voltage VSCd for longer than the short current detection time tSCd plus the comparator settling time tscs, the

corresponding gate driver switches the external Power MOSFET off and the corresponding drain-source

monitoring flag (DS MON LS1, DS MON LS2, DS MON HS1, DS MON HS2) is set. The DSMON_x bits have to

be cleared through the SPI to reactivate the gate drivers. This monitoring is only active while the corresponding

gate driver is activated. If a drain-source monitor event is detected (in Table 55. H-bridge monitoring in off mode is

generically indicated as DS=1, meaning an OR among all four DSMON bits), the corresponding gate driver

remains activated for at maximum the filter time tSCd plus comparator settling time tSCs. The threshold voltage

VSCd can be programmed using the SPI.

Figure 33. H-bridge diagnosis

GH1

SH1

GL1

GH2

SH2

GL2

20k

Gate Driver HS

Gate Driver LS

DS-Monitoring HS

DS-Monitoring LS

OL-Monitoring

VSCd

20k

Gate Driver HS

Gate Driver LS

DS-Monitoring HS

DS-Monitoring LS

OL-Monitoring

VSCd

GND

3.28

H-bridge monitoring in OFF mode

The drain-source voltages of the H-bridge driver external transistors can be monitored, while the transistors are

switched off. If either bit OL_H1L2 (CR12) or OL_H2L1 (CR12) is set to ‘1’, while bit HEN (CR 18) = ‘1’, the H-

drivers enter resistive low mode and the drain-source voltages can be monitored. Since the pull-up resistance is

equal to the pull-down resistance on both sides of the bridge a voltage of 2/3VS on the pull-up high-side and

1/3VS on the low-side is expected, if they drive a low-resistive inductive load (for example motor). If the drain-

source voltage on each of these Power MOSFET is less than 1/6 VS, the drain-source monitor bit of the

associated driver is set. In off-mode monitoring DSMON_HS1 and DSMON_HS2 are not used and set to 0, being

relevant only DSMON_LS1and DSMON_LS2. In case of a short to ground the drain-source monitor bits of both

low-side gate drivers are set. A short to VS can be diagnosed by setting the “H-bridge OL high threshold (H OLTH

High)” bit to one. The open-load filter time (tfOL) is 2 ms typical.

L99DZ320

Functional description

DS14235 - Rev 5

page 73/146

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