L99ASC03 datasheet(22/73 Pages) STMICROELECTRONICS

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Device description

L99ASC03

22/73

DocID023504 Rev 7

Figure 12. HARDOFF functionality by using external dead time

Propagation delay is omitted for convenience.

2.12

Drain-source monitoring

2.12.1

Drain-source monitoring in ON state (short-circuit detection)

The drain-source voltage of each activated external MOSFET is monitored by internal

comparators to detect short circuits to ground or battery. In case the voltage drop over the

external MOSFET exceeds the threshold voltage VSCd, the corresponding DSHS(x) or

DSLS(x) flag is set. In addition, if the DSFT_DIS bit is set to "0", the affected MOSFET is

turned off and the related gate driver is disabled.

The drain-source monitoring has a filter time and is only active when the corresponding gate

driver is in source condition.

The threshold voltage VSCd can be programmed in four steps between 0.5 V and 2 V via

SPI.

2.12.2

Drain-source monitoring in OFF state (open-load / short-circuit

detection)

In Active Mode, each gate driver sources a current of typ. 500 µA at the SHx pins in OFF

condition. By programming the ISTEST(x) bits to "1", a sink current of typ. 800 µA is applied

to the corresponding pin.

By using these internal test currents, an open load, a leakage to GND or to battery can be

detected on each motor phase in OFF state, i.e. without turning on the external MOSFETs.

If the ISTEST_EN bit is set to "1", the drain-source voltage monitoring is enabled also in

OFF condition and the Status Register 7 reflects the result of the voltage comparison (i.e.

drain-source voltage below or above the programmed threshold) in real time (i.e. the status

bits are not latched) and without setting the FE bit in the Global Status Byte. See

Section 2.18: Diagnostics for more details about diagnostics.

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