I would like to design a general use current source for use with shunt dimming. I am basing it on the TPS92515HV with a 48V input and a 2A maximum current output.
I have configured the webbench program to make both have 10% inductor ripple and manually set the output capacitors to 1pF to evaluate a no output capacitor design. I created one design targeting 40Vout at 2A and another design targeting 4Vout at 2A to test the output voltage range.
The two designs come up basically with the same parts within what I expected except for Roff. In the 40Vout design it suggests 105k but the 4Vout design suggests 44.2k. In reading the datasheet, this is consistent with what it calculates there. But what should I do if I want to be conservative and make it work for the full output voltage range? Should I choose the lowest possible Vout for that calculation to ensure that Coff is charged with a low output voltage?
Note that I am using this with TPS92661Q to allow me to control more than one LED from a single supply, so the output voltage may vary quite a bit from application to application.
Since I am using it with shunt dimming, the inductor current ripple looks like 100-200mA with a 330uH inductor with 0.63V for four TPS92661Q switches, which I work out to mean a Toff-shunt of 50 microseconds and an Roff2 of 473k between VCC at 5V and Coff.
