C
Chuck Simmons
- Jan 1, 1970
- 0
I'm using a combination motor driver from Mitsubishi. It has all H
drivers in it. One three phase brushless DC motor driver (12 volt PWM,
transconductance), One two phase stepper motor driver intended for
microstepping (12 volt PWM, transconductance), brush type motor driver
(gain of 8, no PWM, 5 volt) and two VCM drivers (gain of 12, no PWM, 5
volt). This is a highly popular motor driver configuration in a single
42 pin surface mount package.
In using the VCM drivers, I have opamps and a current shunt to allow
current feedback or I can set voltage gain and let the VCM coil
resistance set the transconductance. The two modes are configurable by
either shorting a capacitor and deleting one resistor or the other way.
In the computed open loop response of the VCM servos using an SRS785 (I
think it is) analyzer, I see a gain and phase glitch at about 1KHz. By
opening the loop, the response of the Mitsubishi VCM drivers can be
measured directly. The VCM drivers show a gain/phase glitch at about
1KHz. The VCM specifications indicate no dynamics other than rigid body
from 50Hz to at least 50KHz. Nevertheless, I tested the VCM drivers into
resistors. The gain/phase glitch moved up to about 1.5KHz. The
gain/phase glitch is seen in both voltage gain mode and current feedback
mode for both VCM channels
The mystery is that in VCM drivers I have designed for the same purpose,
I have not had the gain/phase glitch. I have only seen it with the
Mitsubishi part. The frequency is too low to be an internal pole/zero
especially considering the part is intended for 5KHz servos and better.
Anybody have an idea where gain/phase glitch comes from?
Chuck
drivers in it. One three phase brushless DC motor driver (12 volt PWM,
transconductance), One two phase stepper motor driver intended for
microstepping (12 volt PWM, transconductance), brush type motor driver
(gain of 8, no PWM, 5 volt) and two VCM drivers (gain of 12, no PWM, 5
volt). This is a highly popular motor driver configuration in a single
42 pin surface mount package.
In using the VCM drivers, I have opamps and a current shunt to allow
current feedback or I can set voltage gain and let the VCM coil
resistance set the transconductance. The two modes are configurable by
either shorting a capacitor and deleting one resistor or the other way.
In the computed open loop response of the VCM servos using an SRS785 (I
think it is) analyzer, I see a gain and phase glitch at about 1KHz. By
opening the loop, the response of the Mitsubishi VCM drivers can be
measured directly. The VCM drivers show a gain/phase glitch at about
1KHz. The VCM specifications indicate no dynamics other than rigid body
from 50Hz to at least 50KHz. Nevertheless, I tested the VCM drivers into
resistors. The gain/phase glitch moved up to about 1.5KHz. The
gain/phase glitch is seen in both voltage gain mode and current feedback
mode for both VCM channels
The mystery is that in VCM drivers I have designed for the same purpose,
I have not had the gain/phase glitch. I have only seen it with the
Mitsubishi part. The frequency is too low to be an internal pole/zero
especially considering the part is intended for 5KHz servos and better.
Anybody have an idea where gain/phase glitch comes from?
Chuck