[originator]

I ordered some 2184's and HIP4080A IC's today needing to get a bipolar design together. Ideally the 4080 is nice as it is a full Hbridge driver in one IC, with a few extrenal charge pump parts needed. Ok so that brings up a big issue, charge pumps. I have heard that unless the inputs are constantly being pulsed at a minimum of a few hudred hertz that they lose charge, a nd turn of the output until the cap is recharged. The mystery is this, if you are already PWMing a stepper that is not moving, this should be no problem, the cap is constantly being charged based on the PWM freq. But, what if the motor is turning at a speed that and the sense has not kicked in the comp, then what? Is the frequency of the Step inputs enough to work. Every design I see for these type drivers is that there is just a cap and diode, no explanation as to how and when to setup some advanced means to charge the cap, say for example some method to keep the cap charged if the PWM from the processor was not kicking in.

If anyone could make this ramble above make sense for me that would be great. It isn entirely possible that the thing may just work as is. If there is another suggestion for hbridge driver I am open to that as well.

Thanks

[Mariss Freimanis]

It's called a boot-strap, not a charge-pump supply and still just a diode and a cap. Limit the PWM to a 5%/95% modulation (not 0%/100%) and everything works just fine.

Be carful of the HIP4080. It had a nasty habit of failing near it's max rated voltage. We have used over 300,000 IR2104s and we don't have a single documented instance of one failing on its own.

Mariss

[originator]

Ok sounds good, I take it that even if the output is off and the cap is drained, that on a new pulse it charges as needed and no need to deal with that issue of a missed step. The 4080 is rated at around 90, I'd be using it under 30v in these applications, so based on your warning I should be fine if choosing that route. In this application the PWM to the motor is set up as a fixed time off, so the duty cycle is really ignored, it just turns off the motor for 8 pwm pulses for every comp trigger.

Last thing, are you guys PWMing the high and low side from the inputs or shudown in the ir21xx? This actuall sounds wrong, if you don't PWM the high and the low, the outputs shut off if they are supposed to be holding, so the high and low must be pulsed to keep the motor holding if stopped.

They have the Ir2136 which is 3 phases in one IC, may be more economical than two Ir2184s.