L99MH98 datasheet(35/147 Pages) STMICROELECTRONICS

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Protections and diagnostics

5.1

Reverse polarity protection

The output of the charge pump (CPOUT pin) can be used to supply an external n-channel MOSFET, building an

active reverse polarity protection (refer to the Figure 19).

5.2

Programmable cross current protection time (DT)

In any input mode (octal half-bridge mode or full-bridge mode), the device adds the configured dead-time between

the turn-off of a MOSFET and the turn-on of the complementary one (that is, the other MOSFET of the same leg)

to avoid cross-conduction in any of the half-bridges. Two different methods have been implemented to choose the

starting point of the cross-current protection time according to the DTP_REF bit. If the DTP_REF = 0, the cross-

current protection time is calculated starting from the command to switch off a MOSFET and switch on the

complementary. If the DTP_REF = 1, the cross current protection time is calculated starting from the instant in

which the Vgs of the MOSFET being switched off has reached the value set in the VSTEP1x.In octal half-bridge

mode each half-bridge dead-time tDTxxx is independently configurable by control bits DTx[2:0], x = 1...8.

5.3

Short circuit detection/drain source monitoring (DSHS/DSLS)

The voltage-drop over each MOSFET is sensed and compared to a programmable threshold to detect an

overcurrent condition. This monitoring is activated only on the external MOSFETs of the half bridges driven to be

ON. In the L99MH98 each half-bridge has its own programmable threshold (VDS_CONFx[3:0], x = 1...8), blanking

time (VDS_BLANKx[3:0], x = 1...8) and filtering time (VDS_FILTx[2:0], x = 1...8).

As soon as the gate driver starts to turn ON a MOSFET, the corresponding drain source monitoring comparator

output is masked for the programmed blanking time to give time to the MOSFET to turn on. After the blanking

time is expired, a filtering time is applied to filter noise. Both values must be chosen depending on the application.

If the voltage-drop over the driven MOSFET exceeds the programmed threshold voltage VSCdx

(VDS_CONFx[3:0], x = 1...8) for a time longer than the programmed filtering time (and the programmed blanking

time, where applicable), either the gate drivers belonging to the faulty leg are forced to switch off actively the half-

bridge MOSFETs with the maximum available current, regardless of the programmed gate discharge current bits.

In any case the drain source monitoring flag VDSHSx, x = 1…8, or VDSLSx, x = 1...8, of the MOSFET detecting

the fault is set. The drain source monitoring flags must be cleared through SPI to reactivate the affected half-

bridge/full-bridge gate drivers that are forced in disabled mode. The drain source monitoring flag VDSHSx/

VDSLSx can be cleared by an SPI “read and clear” command only if the fault condition is no longer present.

If the voltage-drop over the driven MOSFET still exceeds the programmed threshold voltage VSCdx

(VDS_CONFx[3:0], x = 1...8) for a time longer than the programmed filtering time (and the programmed blanking

time, where applicable) after the SPI “read and clear” command, the drain source monitoring flag VDSHSx, x =

1...8, or VDSLSx, x = 1...8 will be set again. It is up to the microcontroller to decide how many attempts to make

before finally turning off the half-bridges where the over current is present.

L99MH98

Protections and diagnostics

DS14611 - Rev 3

page 35/147

L99MH98 Fiches technique(PDF) 35 Page - STMicroelectronics