ADC channel result error

[sarwath]

Hello Community,

I am trying to read the input supply ( voltage and current) through ADC1. 

ADC1_channel 6 is to sense the Input current and ADC1_channel 7 is to sense the Input voltage.

I am triggering the ADC1 with PDB1,

sarwath_0-1673873225160.png

At beginning I have sensed the ADC1_channel 6 Input current and I got output current_mv as 1290 mv.

sarwath_1-1673873266639.png

Later I added the ADC1_channel 7 Input current,

sarwath_2-1673873382537.png

When I sense the both ADC1 channel, the current_mv result are modified from 1290mv to 537mv .

sarwath_3-1673873517392.png

My voltage_mv is correct as per my requirement but the current_mv values are changing once I added the 2nd channel ADC1_channel 7.

There is no changes in supply but I am getting different ADC result. I have attached my project for your reference. Please have a look and let me know where I am going wrong.

sarwath_4-1673873672974.jpeg

Many Thanks,

Sarwath

[sarwath]

I am suspecting my sample time and PDB timer and delay value. In my project I kept constant sampling time.

How to configure the different sampling time for different channels.

[davidtosenovjan]

Hi, If you don't have some error in SW configuration then it could be possibly caused by high impedance attached to the ADC input.

This device explicitly specify it as 5kOhm (max) at 4MHz (max).

davidtosenovjan_0-1673959209074.png

Do you have it so?

[sarwath]

Hello @davidtosenovjan ,

Yes david. In my Hardware the source impedance is 159Hz. It is less than 4Mhz only.

sarwath_0-1673960596601.png

In RM, I read like,

sarwath_1-1673961085372.png

I am using the back to back method only. I feel my PDB trigger causing the issues. How to calculate the PDB module value and delay values. 

Many Thanks,

Sarwath

[sarwath]

When I use the Software trigger for channel ADC1 CH6 , I am getting ADC result value closer to the Vin.

Then I configure the ADC (2 channels) with PDB trigger I am getting this value mismatch. I am reading RM and implementing but I am getting the wrong value in ch6 and ch7 value is valid (closer to the supply voltage). one channel value is correct and another channel value is wrong.

[sarwath]

Hello @davidtosenovjan ,

I found the root cause of this issue.

I thought to try in different channels (MCU pin) instead of used one (MCU pin 67). Then I checked the continuity of the Pin 67 and there is continuity. 

So I re-soldered the MCU Pin 67 , Now It is working fine. ADC output is equal to Vin.

Many Thanks,

Sarwath