TPS92690: TPS92690 Application Question

Hello Kuo,

There really isn't a minimum or a maximum. It really just depends on what kind of range and linearity is required for the application. For example, if you look at the low duty cycle PWM dimming scope shot in the boost EVM user's guide you will notice the rise and fall times of the LED current. That will limit linearity, minimum duty cycle, and/or maximum frequency. If you go too fast and/or small enough duty cycle you will see that you will get no current. The practical limitation for decent range and linearity is probably around 500Hz, but it really depends on the design (how much output capacitance, inductor value, Vin/Vout, etc...) and would need to be tested for each application.

If you need to have a higher PWM dimming frequency you will need a disconnect FET such as that used with the TPS92691. That makes up to 10kHz or more possible depending on the required range.

Regards,

Clint