Hi team,
We have question about Ilim pin circuit design. And need BU's clarify it.
In general, we always can measure big negative voltage feedback in Ilim pin, around -1.xV. see waveform in below.
So we need to use RC filter to reduce this negative voltage in case to damage our chip.
In our Datasheet, we only use Rlim and Clim in Rdson current sensing topology.
Can we use RC filter for Shunt Resistor Current Sensing topology? And how to decide C value?
Thanks
Paul,
Negative voltage on SW node is always expected in buck converter during the dead-time, the low-side MOSFET will have body diode voltage drop.
This should not cause issue with IC. Note the SW has -5V 20ns spec, and for ILIM sensing SW node that should not be an issue.
For RDSON sensing there is a CILIM capacitor suggestion.
I don't think you should use additional filtering, it should be fine.
Hope this helps,
-Orlando
Paul,
It is fine for transients less than 20ns, just like SW node.
Also, it could be that the scope is picking up switching noise, be sure to use a tight loop on your scope probe for most accurate voltage level measurements.
Hope this helps,
-Orlando
