Info and sample schematic request for L9352 low side switch IC

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is_razi

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Hi Board,
Is there anybody who has worked and done any projects with ST's quad low side switch ,L9352 IC? I am trying to design a valve drive with this IC but I have problem with the regulated channels . The unregulated channels work as they should but for the regulated channels 3 & 4 the output pulse length doesn't change as I change the input pulse duty cycle and the switches of these channels are just on for about 90% of the cycle. unfortunately I couldn't find much about this switch and the only documents are the ones in the ST's website which are not enough explanatory. Any information , schematic and experience is welcome.
Thanks .
 

Solution
Hi,

Resistive load --> yes you need some inductivity to make it work properly.

No, I have no experience with this specific IC.
Schematic: No big deal: Just a couple of capacitors. see Fig1. of AN2791.

Supply:
VDD and VSS are both internally used and should be 5V
VS is most probably used for driving the internal MOSFET gates.
The voltage at the outputs Q may be 40V continously. Thus I see no problem with 24V as valve supply. But you need a proper PCB layout, proper power supply bypassing and fast free wheeling diodes for the valves.
I´m a designer for reliable circuits, thus I´d add fast overvoltage protection at the Q pins (just for very fast, low power transients) .. but indeed there are inside zeners to the gates, thus it...
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KlausST said:
Hi,

did you read AN2791?

Klaus
Click to expand...
Hi, thanks for your response ,I should say yes I did. In fact it's more about the regulator accuracy. But I should say I solved the problem, I was using pure resistive load instead of a valve.
May I ask you if you have done any project with this IC? If so could you share the schematic or do you have the schematics of the ST's experimental boards? And one more question , can I use different voltage levels for the Vs (internal supply) and the voltage I apply to the valves terminals . Because to inject the required current to the valve I need to supply it with 24 volt but the Vs 8s limited to 18volt .
Thanks for your
 

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Hi,

Resistive load --> yes you need some inductivity to make it work properly.

No, I have no experience with this specific IC.
Schematic: No big deal: Just a couple of capacitors. see Fig1. of AN2791.

Supply:
VDD and VSS are both internally used and should be 5V
VS is most probably used for driving the internal MOSFET gates.
The voltage at the outputs Q may be 40V continously. Thus I see no problem with 24V as valve supply. But you need a proper PCB layout, proper power supply bypassing and fast free wheeling diodes for the valves.
I´m a designer for reliable circuits, thus I´d add fast overvoltage protection at the Q pins (just for very fast, low power transients) .. but indeed there are inside zeners to the gates, thus it should be self protecting.

Show us your PCB design...

Klaus
 

    is_razi

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Solution
Dear Klaus , thanks for your hints, I applied slightly different voltages to VS (17v) and the Q pins (19.5v) and it seems it's working properly . There are free-wheeling diodes at the output , do you think it is still necessary to consider external protection diodes?
 

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Hi,

there is an overprotection zener diode inside and the MOSFET body diode, but no true freewheeling diode.
I recoomend to add a freewheeling diode across the valve. It also saves power and reduces dissipated heat.
It creates a slow decay instead of the fast decay generated by the zener.

As already written there is no need for additional external protection .. you may add it, but there is no must.

Klaus
 

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