Oznog
Active Member
Back to a project I mentioned earlier-
I need to make a PWM to power a buck regulator for extremely high powered LED emitters (in the amps range). It will use an external PMOS transisor. The output must be current regulated, and the shunt resistor will need to be very small to avoid heating up. It needs to be able to do 0%-100% duty cycle. Size is a factor and I need to do this with as few components as possible. It would be nice to keep it cheap, under $2 per PWM channel.
Actually there will be 3 separate PWM channels, the only thing the same will be the freq.
It looks like all the PWMs with "2 outputs" or "4 outputs" are always just drivers for multiple transistors for the same channel, not what I need. I guess I can use 3 chips as long as they're 8 pin, but I'd love to find a multiple output channel PWM. Also, the voltage feedback compares internally against a higher voltage than the current shunt would drop, like 1v-2.5v instead of the 0.1v-0.25v the shunt might make. Ideally, I would like to have a chip with an external reference so the shunt voltage doesn't have to go through an op amp. Not only do I dislike adding 3 op amps and feedback resistors, I'm not sure how stable it would be putting another op amp in series with the amp inside the PWM chip.
So I'm looking through Digikey/Mouser for PWM chips and there are hundreds and hundreds here. I've gone bonkers searching through them, first off looking for that external reference in the feedback loop, and have only seen a fraction of them so far. Mouser's search engine is just awful, gives me 100 pages of stuff with no way to do filtering (eliminate TSSOP-20 pkgs, $5 parts, etc) that I can see.
Could somebody help me out here? What's a decent PWM chip that will fit the bill?
I need to make a PWM to power a buck regulator for extremely high powered LED emitters (in the amps range). It will use an external PMOS transisor. The output must be current regulated, and the shunt resistor will need to be very small to avoid heating up. It needs to be able to do 0%-100% duty cycle. Size is a factor and I need to do this with as few components as possible. It would be nice to keep it cheap, under $2 per PWM channel.
Actually there will be 3 separate PWM channels, the only thing the same will be the freq.
It looks like all the PWMs with "2 outputs" or "4 outputs" are always just drivers for multiple transistors for the same channel, not what I need. I guess I can use 3 chips as long as they're 8 pin, but I'd love to find a multiple output channel PWM. Also, the voltage feedback compares internally against a higher voltage than the current shunt would drop, like 1v-2.5v instead of the 0.1v-0.25v the shunt might make. Ideally, I would like to have a chip with an external reference so the shunt voltage doesn't have to go through an op amp. Not only do I dislike adding 3 op amps and feedback resistors, I'm not sure how stable it would be putting another op amp in series with the amp inside the PWM chip.
So I'm looking through Digikey/Mouser for PWM chips and there are hundreds and hundreds here. I've gone bonkers searching through them, first off looking for that external reference in the feedback loop, and have only seen a fraction of them so far. Mouser's search engine is just awful, gives me 100 pages of stuff with no way to do filtering (eliminate TSSOP-20 pkgs, $5 parts, etc) that I can see.
Could somebody help me out here? What's a decent PWM chip that will fit the bill?
