HPWM problem .. pls help!

[NavMicroSystems]

L293D Datasheet

[anj]

Gday
Interesting.
I have an original Unitrode datasheet, and a quick search brings up the current texas one http://focus.ti.com/docs/prod/folders/print/l293d.html
Neither of these specify a 5KHz limit.
They mention doing their rise/fall time measurements at 5KHz, but thats all.
Based on the actual rise/fall times ( your link vs texas link ), they appear to be close, so i am at a loss to understand the difference.
I certainly have run my 293D at higher than 5KHz before.
Dunno

[Samuel]

Well right now after playing for a whole afternoon with different conbinations of duty cycle and frequency, the HPWM 1, 135, 3000 seems to work well for me .. at high frequencies my motors start doing funny stuff .. I feel this may have to do with the how the 293D is setup. I have my two PWM lines, one going into each of the enable. And then 4 control lines, 2 for each motor. There is another way of setting up, which can reduce the number of lines by using an Inverter. Since this setup is working for me, and i have enough ports on my PIC controller, i'm not gonna try that for now ... I just have to find someway to keep the 293D cool .. Someone suggested to use some kinda paste .. tooth paste??? And then what?

[anj]

Someone suggested to use some kinda paste .. tooth paste???

Thermal transfer paste ( heatsink paste ). And a big heatsink.

And then what?

Go for a dedicated H Bridge using N and P channnel mosfets.
Using one PWM channel and some pulldown diodes ( from between the gates current limiting resustor and the gate, back to a PIC pin ), you can control where the PWM goes, hence dirn.
Andrew

[Bronurstomp]

Micrel makes a very good set of mosfet gate driver chips. Find their data sheets here. http://www.micrel.com/_PDF/mic4423.pdf
They are dual output, so you would need 2 of them for 4 outputs. Again these will drive N-channel Mosfets (low side is motor to ground connection).

If you want to use P channel Mosfets on the high side (Motor to power connection), then you'll need some kind of high-side driver like Linear's LT1161, which does all the charge pumping for you.
Their datasheet is here.

http://www.linear.com/pc/productDeta...42,C1041,P1387

Happy motoring!