Re: L297 L298 sense circuitry

JJ

Anytime a bridge switches, there will be a current spike on the
leading edge of the change of state. Some of this will be reverse
recovery shoot-thru diode currents, capacitive line charge and
discharge currents, etc.

The result is what happens in the first 200nS after the edge is ugly;
current are spikes easily 10 times what the ultimate value will be.

The RC filter softens the spikes to some degree so as not to fool the
sense comparator into prematurely terminating the switching cycle.

This works to a greater or lesser degree if the filter is chosen
carefully. What works much better is having a blanking period. This
means the comparator is disabled for a period of time (2uS to 5us)
after the edge. When it re-enables, all the transients have passed
and the sense signal is steady again.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "JJ" <jj5412@e...> wrote:
> Some schematics for the L297/L298 show a resistor and cap from the
sense
> resistors to the L297, others show a direct connection. Can anyone
tell
> me what the R/C do for you, and what values to use?
>
> Any help appreciated!
>
> ADVthanksANCE,
> JJ
>
> Be Kind, Be Careful, Be Yourself