ST AN279 Application note
AN279
APPLICATION NOTE
SHORT CIRCUIT PROTECTION ON L6203
by G. Scrocchi and G. Fusaroli
With devices like L6203 used as driver often interfacing the external world by means of wires, can be easy to
have short circuits.
A short circuit can occur for many reasons : a short on the load, a mistake during the connection of the wires
between the device and the load (i.e. L6203 driving a motor), an accidental short between the wires and so on.
The outputs of L6203 are not protected against the short circuit and if a short occurs, the big amount of current
flowing through the outputs can destroy the device.
To avoid this risk can be useful to add a circuitry to protect the device : in this case, to have a total protection,
we must consider three types of short circuit :
1 - output to output short circuit
2 - output to supply voltage short circuit
3 - output to ground short circuit
The first step is to sense the short circuit current. In output to output (fig 1) or output to supply (fig 2) short circuit
can be used the sensing resistor (Rsl) already used to set the current flowing in the load during the normal operation.
Figure 1.
Figure 2.
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AN279 APPLICATION NO TE
To sense the output to ground short circuit (fig 3) another sensing resistor (Rsu) must be added betw een the
supply pin and the supply voltage.
Figure 3.
The second step is to create a threshold over which the value of the current must be considered as short circuit:
for this way a transistor or a diode could be used.
The complete protection will be given by the ’ or ’ of the signal coming from the upper and the lower sensing
circuitry ; this signal can be used to act on the ENABLE pin of the L620 3 disabling the output stages. A com plete
protection schematic diagram is shown in fig. 4.
Figure 4.
In normal operation the circui t works up to 3A/40V. When a short circuit occur s the SCR is triggered and L6203
disabled : due to the SCR memory L6203 is kept disabled until the power is switched off and then on, if the
cause of short was removed.
The short circuit is detected when :
V
I
SU
BE T1()
-------------------- -
>
R
SU
0.6
------- - 6A==
0.1
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