AN279

2/5

Doc ID 1702 Rev 2

the supply pin and the supply voltage as shown in Figure 3.

Figure 3.

Short-circuit from output to ground

The second step is to set a threshold over which the value of the current to be considered as

short-circuit. An easy threshold is to select the forward bias voltage of a diode or transistor.

When the voltage across the sense resistor exceeds the Vf or Vbe, the device turns on

indicating an overcurrent from the short-circuit.

The overcurrent signal from both the upper and lower sense resistor are ORed together to

trigger the shutdown to protect the device. One simple way to shutdown the device is to take

the enable line low and latch it low. The circuit in Figure 4 uses an SCR that will latch on and

hold the enable low if an overcurrent occurs. The figures show the L6203, but the same

configuration may be used with the L6201 or L6202.

Figure 4.

Short-circuit protection circuit

In normal operation the circuit can work up to 3 A/40 V. When a short-circuit occurs the SCR

is triggered and the L6203 is disabled. Due to the SCR memory, the L6203 is kept disabled

until the power is switched off and back on, if the cause of short was removed.

The short-circuit is detected when:

Equation 1

I

SU

V

BE T1

()

R

SU

--------------------

>

0.6

0.1

--------

6A

==

I

SL

V

D

V

THSCMT

+

R

SC

---------------------------------------

>

0.6

0.7

+

0.165

-----------------------

7.8A

==