ADS5482: Reference voltage at input voltage

Hi Balvan,

You are correct that the VCM should be a stable 3.1V. Is this fluctuation following a pattern or is it random? Can you provide an oscilloscope capture of this behavior?

Can you verify that the ADC is not expecting an external reference by measuring the voltage at both the PWDNF and PWDNS pins? What are the measured voltages at VCM (pin 16) and VREF (pin 4)?

Also, please note that the PDWNF pin is not connected to ground through a pull-down resistor, which might change your default operating mode from "Deep sleep" to "ADC ON - External reference".

Regards

Hi Chase W,

The fluctuations pattern is random, some time voltage is stable at 3.1V and some time it gets drop to 0V and some time fluctuated between 0v to 3.1V. I have measured this voltage through a multimeter.

I have measured the voltage at PWDNF, PWDNS both have zero volts.

VCM (pin 16 ) voltage is around 3.1V and VREF (pin 4) voltage is around 1.2V.

PDWNF pin is not connected to ground as Resistor R304 is DNI (Do not insert) .

What could be the possible reason for not stable reference voltage at the input pin?

Hi Balvan,

Can you check whether or not the VCM at pin 16 also drops when the input voltage fluctuates? 

A few other things you might try is to isolate the ADC (remove R351, R354) and check if the behavior remains the same. Also, you can increase the value of the C681 and see if this helps stabilize the common mode voltage.

Hi Chase, when the reference voltage input pin was zero, then I checked both VCM and Vref pin voltage, both pins showing 3.1V and 1.2V respectively

Balvan, can you provide captured data without a signal applied? Any format is fine. I have sent a private message with my email address.

Balvan,

Can you try using an external reference on a bad part to see if this helps? Another suggestion is to reflow the ADC on your board; ensure the power pad is making good contact.

Can you send us the power supply portion of your design as well? (Upload via image/ email pdf to me)

Also, if you would like to send us one of the bad parts, we can swap it onto one of our lab EVMs for testing.

Please try these suggestions and let us know if anything improves.

Thanks, Chase

Hi Chase W, I already removed R351 and R354 resistors then why do you need Low pass filter circuits. As I said The behaviour of IC is random so I will share one more file for your better understanding.

Another thing is when I say results are improved it doesn't mean that issue got resolved. I am still facing the issue and we can not meet customer requirements because of the Randomness of ADS5482 IC.

Dear Chase 

Thank you for the quick response.