Re: [CAD_CAM_EDM_DRO] Want some help about L297 chip

On Mon, 20 Oct 2003 00:14:31 -0500, you wrote:

>
>
>yours_salman2002 wrote:
>
>>Hello users
>> I am using L297 in my project for first time,therefore i
>>want some help.I want to set it's chopping frequency to 20Khz so
>>which values should be used for resistor and capacitor?
>> I see its formula but i can't solves it :( .
>>another thing is i use four IRF540 mosfets with L297 and i set L297
>>chopper mode to phase type not (INH)type so did it works with 8AMP
>>stepper motor? also i don't uses INH1 INH2 outputs but i use sense
>>inputs.
>>
>>
>I don't think you can set the chopping frequency that way. It depends on
>the inductance of the motor winding, the power supply voltage, and the
>hysteresis of the current sensing amp.

This is not my understanding of the way it works. The 297 can be
driven by an external clock signal for chopping, so that would rule
the frequency setting by motor inductance, voltage, and hysteresis
out.

However, the inductance, supply voltage, and hysteresis will have an
effect on the current rise rate in the motor windings, and the
ultimate current reached in the motor windings. You can make a very
valid argument that the chopping frequency can be set so high that the
motor will not easily reach full current in the amount of time
allowed.

the formula gives f = 1/(0.69 * R * C) .

IF R is in ohms, C in farads, f will be in hertz.

R in K ohms, C in microfarads, F will be in Khz.

R must be at least 10000 ohms.

Harvey

>
>Jon
>