DocID07617 Rev 4

13/29

L6206

Circuit description

29

5.3

Non-dissipative overcurrent detection and protection

In addition to the PWM current control, an overcurrent detection circuit (OCD) is integrated.

This circuit can be used to provide protection against a short-circuit to ground or between

two phases of the bridge as well as a roughly regulation of the load current. With this

internal overcurrent detection, the external current sense resistor normally used and its

associated power dissipation are eliminated. Figure 9 shows a simplified schematic of the

overcurrent detection circuit for the bridge A. Bridge B is provided of an analogous 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 ISOVER 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 OCD pin is turned on. Figure 10 shows the OCD operation.

This signal can be used to regulate the output current simply by connecting the OCD pin to

EN pin and adding an external R-C as shown in Figure 9. The off time before recovering

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

logic inputs.

IREF and, therefore, the output current detection threshold are selectable by RCL value,

following the equations:

–ISOVER = 5.6 A ± 30% at -25 °C < Tj < 125 °C if RCL = 0  (PROGCL connected to GND)

–ISOVER =

±10% at -25 °C < Tj < 125 °C if 5 K RCL < 40 k

Figure 11 shows the output current protection threshold versus RCL value in the range 5 k

to 40 k

.

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 12. 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 13.

Table 7. Truth table

Inputs

Outputs

EN

IN1

IN2

OUT1

OUT2

LX(1)

1. X = don't care.

X(1)

High Z(2)

2. High Z = high impedance output.

High Z(2)

HL

L

GND

GND

HH

L

Vs

GND

HLH

GND

Vs

HH

H

Vs

Vs

22100

RCL

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