L6228Q datasheet(19/32 Pages) STMICROELECTRONICS

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L6228Q

Circuit description

Doc ID 14321 Rev 4

19/32

Figure 20.

Wave drive mode

4.9

Non-dissipative overcurrent protection

The L6228Q integrates an overcurrent detection circuit (OCD) for full protection. This circuit

provides protection against a short circuit to ground or between two phases of the bridge.

With this internal over current detection, the external current sense resistor normally used

and its associated power dissipation are eliminated. Figure 21 shows a simplified schematic

of the overcurrent detection circuit.

To implement the over current detection, a sensing element that delivers a small but precise

fraction of the output current is implemented with each high side power MOS. Since this

current is a small fraction of the output current there is very little additional power

dissipation. This current is compared with an internal reference current IREF. When the

output current reaches the detection threshold (typically 2.8 A) the OCD comparator signals

a fault condition. When a fault condition is detected, the EN pin is pulled below the turn off

threshold (1.3 V typical) by an internal open drain MOS with a pull down capability of 4 mA.

By using an external R-C on the EN pin, the off time before recovering normal operation can

be easily programmed by means of the accurate thresholds of the logic inputs.

D01IN1321

4682468

IOUTA

IOUTB

CLOCK

Start Up or Reset

L6228Q Datenblatt(PDF) 19 Page - STMicroelectronics