PGA411 : possibility to use a external exciter signal

Pascal,

Yes, what you are suggesting should be possible. I need a little time to put together the configuration details and test it, so I will get back to you by Wednesday. The following are my initial comments:

When using the auto-phase correction mode, the PGA411-Q1 uses the signals from IE1/IE2 to monitor the phase. If you use manual phase or no phase correction, then an internal signal is used as the reference, and connecting external signals to IE1/IE2 will not work. So you must use the auto-phase mode.

I do not think that there is a way to turn off the exciter amplifier while keeping the tracking loop active with register settings. It should work if you disconnect the VEXT supply and keep FAULTRES low (FAULTRES low will tell the PGA411 to ignore all fault conditions). Would that be an acceptable solution? Do you need any of the diagnostic or safety features of the PGA411?

The other option would be to let the exciter amplifier run without connecting anything to it. The disadvantages with this solution is that power consumption would be slightly higher and you would have to populate the boost components.

Thanks,

-Clancy

Clancy, 

Yesterday,I've deployed this configuration.

A motor controler produces the exitaton signal (6Vpp, 10 kHz) connected to the Ie1, Ie2 of the PGA411 inputs and to the motor resolver.

Oe1, Oe2 pins are not connected. 

The resolver signals (sin/cos) to the IZn pins. 

A ocilloscope is connected to the AOUT analog output.

The PGA411 registers ares programmed with the nominal configuration. 

The system works perfectly but stills instable for 90, 180, 270 °. 

In a second time, I've modifed the DEV_PHASE_CFG register and put the APEN bit to 0 (Automatic phase control disabled). 

The phase regulation in the PGA411 becomes stable from 0 to 359°. 

Are you agree with this configuration? 

Concerning the possibility to turn off the exciter amplifier : 

I don't need any of diagnostic or safety features of the PGA411. 

Thanks, 

Pascal

Pascal,

Are you scaling down the voltage at the IE pins with a resistor divider? If you are doing that, the set-up looks good.

When using APEN = 1, you should keep AUTOPHASE_CFG = 00; otherwise you may run into the instability issue that you noticed. What were the default values of AUTOPHASE_CFG that you used when you had the issue?

Thanks,

-Clancy

Clancy, 

No,

I modified the values of the IE resistors in the Analog Front End.  27.0k replaced by 10.0k. The goal was to increase the inut gain. 

It's seems to be better but the instability issue stays around 90, 180, 270 ° again. 

The AUTOPHHASE_CFG value was to 00 (the factory settings);

Since two weeks ago , we are using the configuration : 

PDEN and APEN bits are to 0. 

The angle measurement seems to be stable for all the rotation of the resolver. 

Are you agree with this configuration?

Thanks,  -Pascal

Pascal,

That should be fine. Manual phase delay mode (PDEN = 1), will not be an option since you are using an external exciter signal. I am not sure why autophase mode is not working properly. It might have something to do with the input signals back to the IEx pins.

How large is the phase delay between the IEx pins and the IZx pins (you can also measure it at OSIN/OCOS)?

Thanks,

-Clancy