We have a product using the TPS61181 to run four LED strings in a 5" display product. I saw one of them on broadcast TV last Sunday, and the 220Hz PWM backlight modulation is strobing very badly with the TV cameras. We can't increase the frequency enough to get around this, so I was wondering if I can put a "variable resistor" on the ISET pin, and control the brightness that way.
There's nothing obvious in the specifications giving the minimum LED current (corresponding to the maximum ISET resistance) that the chip will work at. I'm guessing that's implied by the switching power supply design and inductor selection, but a quick pointer would help here.
The easiest "variable resistor" would be a current mirror driven from a filtered PWM voltage. I could design this with discretes, but a pointer to a TI chip that can act as a "voltage controlled current sink" over the range of 15uA (replacing 82k) down to zero and App Notes demonstrating this function would also help a lot.
Tom
