We have used ADG5462F part in our design as ADC Channel protector. We are facing issue with its functionality as we are not getting expected output for the applied input.
Eg: When we are giving 6V as input, we are getting some random voltages at its output. Some channels are giving 9.9V, 11.25V . 1.2V, 0,3V for the same 6V input.
Schematic is attached for your reference. Could please suggest what could be the root cause for this issue. Same ADC is working for differential Channels where we have not used this protector
Awaiting of your response
Thank you for contacting Engineerzone.
Initially I do not see anything obviously wrong with your schematic.
Are you using the TSSOP device or the LFCSP? your pin out is consistent with the TSSOP but I notice you have an EP pin in your schematic. The TSSOP does not have an EP pin.
Do you have any scope plots you could share with me? This would help me to debug the issue.
Thanks for your reply.
We are using LFCSP package part. It has exposed pad connected to GND_A net in our design which supposed to be connected to -15V as recommended in datasheet.
Is this wrong connection causing this issue?
We checked resistance between GND_A and -15V,. It is 84K ohm.
We have measured -15V rail with respect to GND_A net.. It is -15V. No voltage drop.
Random voltages measured at the other end of resistors R445, R446, R447 and R448 by applying 5V DC to input ends of the same resistors.
I can capture waveforms and share you for your analysis if this EP pin wrong connection is not root cause for this issue. Please confirm.
Can you check your pin outs? from your schematic it looks like you are using the pinout for the TSSOP package. The pin numbers are not the same for TSSOP and LFCSP. see image below from datasheet.
In your schematic pin 1 is NEGFV, for LFCSP Pin 1 is S1.
Thank you David.. I got the root cause.