UC1845: how to pick RT/CT values

Hey Yue,

The numbers you talk about are just recommendations, if there is a need to go to a higher switching frequency you can certainly try different values.

My suggestion would be trying to go lower with resistance rather than capacitance.

Thanks,

Daniel

Hi Daniel,

Thanks for the reply. I was trying to lower the capacitance value because I saw that in the Pin Functions Table, it says "Never use a timing resistor less than 5Kohm". (datasheet Pin Functions Table RT/CT) So I guess that's an absolute constraint on the resistor RT. Is that true?

Thanks,
Yue

Hey Yue,

I believe that the comment in the pin functions table is simply referring to the 5k recommendation, but you can always be safe and use capacitance lower for now.

I believe the real issue lies in the fact the clock ramp signal will become somewhat non-linear due to being an RC curve with really small values used. This may cause problems the clock changing over temperature, but that is something that would need to be tested in circuit.

Thanks,
Daniel