Circuit description

L6227Q

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4.6

Non-dissipative overcurrent protection

The L6227Q integrates an overcurrent detection circuit (OCD). 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 14 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

output current in one bridge reaches the detection threshold (typically 2.8 A) the relative

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.

Figure 14.

Overcurrent protection simplified schematic

recovering normal operation can be easily programmed by means of the accurate

Figure 17.

disable time.

+

OVER TEMPERATURE

POWER SENSE

1 cell

POWER SENSE

1 cell

POWER DMOS

n cells

POWER DMOS

n cells

HIGH SIDE DMOSs OF

THE BRIDGE A

FROM THE

BRIDGE B

OCD

COMPARATOR

OCD

COMPARATOR

TO GATE

LOGIC

INTERNAL

OPEN-DRAIN

40

Ω TYP.

µC or LOGIC

D01IN1337