L6208Q datasheet(20/34 Pages) STMICROELECTRONICS

20 / 34 page

Circuit description

L6208Q

20/34

DocID018710 Rev 3

Figure 18. Half step mode

Figure 19. Normal drive mode

Figure 20. Wave drive mode

5.9

Non-dissipative overcurrent detection and protection

The L6208Q device integrates an overcurrent detection circuit (OCD). With this internal

overcurrent 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 overcurrent detection, a sensing element that delivers a small but precise

fraction of the output current is implemented with each high-side power MOSFET. 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 5.6 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 MOSFET 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.

L6208Q Datasheet(PDF) 20 Page - STMicroelectronics