PGA411-Q1: PGA411

Hi,

Thank you for your fast answer. I have one more question: we want to use the AB encoder output, but at low RPM it is very noisy. Even if the motor is stopped, we get sporadic signals on A or B output (pin 1 and 2).

At the same time the signals are very clear and reflecting the motor rotation speed and direction on ORD3, ORD4, ORD5 pins (U1, V1,W1 pins 54,53,52). What can be the problem?

AOUT is connected to GND,

BMODE0 is connected to 3.3V through 4k7,

OMODE is GND through 4k7,

VA0 GND through 4k7,

VA1 3V3 through 4k7,

INHB 3V3 through 4k7.

Attila

HI Attila,

Thank you for the detailed information. I need some time to replicate this and get back to you. I should be able to get back to you by middle of next week.

Meanwhile, do you have an option to read the angle from SPI? If yes, is it stable?

Regards

Sharath.

Hi Attila,

Did you get a chance to read from the SPI register? 

Here are some of the things you can try to see if it helps.

1. Increase the Exciter amplifier gain. You can choose the highest gain. 

2. Try selecting the 7Vrms output

3. Change the resolution to 8 bits by connecting the BMODE0 to ground.

Let me know if any of these help?

Regards

sharath.

Hi,

SPI communication working fine, sometimes we get CRC errors, than we try to change the CRC based on this document http://e2e.ti.com/support/sensors/f/1023/t/774733?PGA411-Q1-PGA411-CRC6-error , but this gives more failures.

We tried to increase the exciter output to 7V RMS however our Vext is 12V, and based on datasheet, in this case 4V RMS recommended - no better result.

We try to increase the exciter amplifier gain and to reduce the resolution to 10 bit, but AB output still noisy.

If we read out the motor angle from SPI registers than it is looks good, but AB output has a very big jitter.

DEV_STAT1 always read as 0
DEV_STAT3 always read as 0
DEV_STAT4 some time read with SPI_ERR flag and some time with FEXTMONL flag
DEV_STAT7 always read as 0x004B

The frequency is 10kHz

Attila

Hi Attila,

Is there any progress towards debugging the issue. I couldnt reproduce your issue with the provided conditions. I will be out of office until 1st sep, so, please expect my response after that. 

Thank you

Sharath.

Hi Sharath,

in continuation of this topic I wanted to give some clarification.

we have problems with RTD at low speed and when the motor is not rotating at all. A/B lines of encoder interface (pin 1 and 2) behave sporadically.

In the best case, we have a constant generation of random pulses on one of the lines (A or B), this situation was also observed on the evaluation board. At worst case, the generation takes place on two lines (as shown in the video below).

https://youtu.be/12ONgcWMAfw

This behavior is observed with different settings and parameters of input filters.

When reading an angle using the SPI, the value is static within one degree.

I didn't found information about behavior of RTD at low rotation speed.

Igor

Hi Igor,

Thanks for the video and detailed explanation. I apologize for the delayed response.

I agree with that the datasheet doesnt have much information for the low rotation speeds. I need to find this information as well.

Is there any chance that you can do the same experiment using the PGA411 EVM?

I have contacted our designers to look into this. I will get back with some input by next week.

Regards

sharath.

Hi Sharath,

It was a hardware issue on excitation output/feedback. As all failure bits were masked, the PGA411 never stopped, even if an error occurs, this is why we gat garbage on AB output. Now the situation is much better, but there are still a jitter on AB, even in low resolution mode (10 bit mode). We need to investigate, if this jitter is caused by a mechanical problem (motor resolver), the motor is driven with a jitter, or this jitter is caused by some noise on SIN/COS inputs.

Attila 

Hi Attila,

Thanks for the update. Let me know if need any help regarding the fault bits and other device related infomation.Please refer to the link on how to interpret the faults and the AFE design http://www.ti.com/lit/pdf/slaa710.

I wouldnt be able to reporduce the same issue here as i dont have the exact setup. Please keep us updated.

Also, what is the minimum speed at which the OUT AB makes sense?

Thanks

Sharath.