L6206Q datasheet(11/27 Pages) STMICROELECTRONICS

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L6206Q

Circuit description

4.3

Non-dissipative overcurrent detection and protection

The L6206Q 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 9 shows a simplified schematic of the overcurrent

detection circuit for bridge A. Bridge B is provided with 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 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 Isover, the OCD comparator signals a fault

condition. When a fault condition is detected, an internal open-drain MOSFET with a pull-

down capability of 4 mA connected to the 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

the 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 the RCL value,

following Equation 1 and Equation 2:

Equation 1

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

Equation 2

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

.

Table 6. Truth table

Inputs

Outputs

IN1

IN2

OUT1

OUT2

X(1)

1. X = Do not care.

X(1)

High Z(2)

2. High Z = high impedance output.

High Z(2)

GND

22100

RCL

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