L6235PD datasheet(22/35 Pages) STMICROELECTRONICS

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Non-dissipative overcurrent detection and protection

L6235

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DocID7618 Rev 2

Non-dissipative overcurrent detection and protection

The L6235 device integrates an “Overcurrent Detection” circuit (OCD) for full protection.

This circuit provides output to output and output to ground short-circuit protection as well.

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

and its associated power dissipation are eliminated. Figure 19 shows a simplified schematic

for the overcurrent detection circuit.

To implement the overcurrent 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 ISOVER = 5.6 A) the OCD

comparator signals a fault condition. When a fault condition is detected, an internal open

drain MOS with a pull down capability of 4 mA connected to pin DIAG is turned on.

The pin DIAG can be used to signal the fault condition to a

C or to shut down the 3-phase

bridge simply by connecting it to pin EN and adding an external R-C (see REN, CEN).

Figure 19. Overcurrent protection simplified schematic

Figure 20 shows the overcurrent detection operation. The disable time tDISABLE before

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

thresholds of the logic inputs. It is affected whether by CEN and REN values and its

magnitude is reported in Figure 21. The delay time tDELAY before turning off the bridge when

an overcurrent has been detected depends only by CEN value. Its magnitude is reported in

Figure 22.

CEN is also used for providing immunity to pin EN against fast transient noises. Therefore

the value of CEN should be chosen as big as possible according to the maximum tolerable

delay time and the REN value should be chosen according to the desired disable time.

L6235PD 数据表(PDF) 22 Page - STMicroelectronics