Re: [CAD_CAM_EDM_DRO] PWM stepper driver with external bridge

Lawrence Glaister wrote:

> Background:
> I am designing a microstepping stepper drive system for a home cnc router
> table (4 axis). The design involves a pic16f84 driving 2 Allegro a3955sb
> motor driver chips (one for each phase). The controller ic is only rated
> for
> 1.5A max phase current and I need 3-5amps for the motors I have. I would
> like to use a full bridge consisting of irf9530 and irf530 fets to act as
> external amplifiers for the controller. I contacted Allegro tech support to
> see if they had any application notes or other comments on using external
> bridges with the 3955 and their rather short response was "the 3955 is not
> suitable for driving capacitive loads". OK... if the chip cannot drive a
> 1600pf gate load of a couple of fets, I would even consider using discrete
> buffer transistors in the external bridge cct.
> Question:
> does anyone have any recommendations or suggestions on using external fets
> with any of the stepper controller IC's? Pitfalls? Example bridge ccts?
> Examples of bullet proof bridge ccts suitable for pwm at 25khz, 5a, 60v?

A great chip is the IR 2113 and others in the same series. I am using two of
them as the full-bridge drivers in my PWM servo amp at 100 KHz, 5-10 A.
They will handle up to 500 V. There is the IR2130, I think, that drives 3
half bridges. Two of those will do 2 full-bridge circuits.

These are just FET drivers, with some undervoltage lockout and cross-conduction
deadtime circuits, but could be hooked to other chips that generate the
PWM signals. The IR21xx series mostly need high-voltage logic
signals, from 12 - 15 V for a logic high, so the stepper driver chips
might work fine for this.

Jon