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AD9364 Supply Issues

We are facing the same issues as per EZ Question here.

https://ez.analog.com/wide-band-rf-transceivers/design-support/f/q-a/79153/ad9364-vdd1p3_bb-power-supply

1P3_SUPPLY_A is Ok (1.3 V)

But, we are getting 1.54 V at 1P3_SUPPLY_B net. When we remove FB19 & FB20, the supply goes back to 1.3V to all the other rails being checked at R63/FB18/FB21.

On removing FB19 & FB20, we are getting 1.8V at these two nets 1P3_TXA & VDDA_RX_TX. What could be the reason?

Please refer to the pdf attached.

What is the solution to this, since the answer posted in above link says it has been answered privately.

Need speedy response as the Gerber is under modification.

PDF



updated
[edited by: Sudhanshu at 8:34 AM (GMT -4) on 29 Oct 2021]
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  • Can you share with us the full schematic so that we can look through in detail?

  • Unfortunately I am unable to share full schematic here. Doesn't the current schematic pages shared gives any idea?

  • These two nets 1P3_TXA & VDDA_RX_TX are giving the extra voltage that is causing the 1P3_SUPPLY_B  net to go to 1.54V. Check these two nets and also  make sure that the supply pins are properly decoupled from each other.

  • Dear Srimoyi,

    Do you mean that we need to give 1.3V from separate two more regulators to these two nets 1P3_TXA & VDDA_RX_TX. As per attached schematic sent, 1.3V is given to these two nets from 1P3_SUPPLY_B.

    Decoupling capacitors are already placed at these two nets 1P3_TXA & VDDA_RX_TX, and ferrite bead BLM18EG221SN1D are also placed between these two nets.

    Do these two nets 1P3_TXA & VDDA_RX_TX always gives out extra voltage? We did remove FB19 & FB20, and 1P3_TXA  & VDDA_RX_TX net are having 1.8V. Why so? As we remove these two ferrite beads (FB19, FB20), 1P3_SUPPLY_B is OK at 1.3V without 1.3V going into 1P3_TXA & VDDA_RX_TX nets.

    We don't know further how to proceed on this. Kindly guide.

  • Can you remove the ferrite beads one by one and then check exactly which net is giving issue? Then replace that bead with a zero ohm resistor and then check if you are seeing the same issue? Check if that net is connected to the 1.8V VDD_INTERFACE and drawing current from there.

    Instead of using a multimeter, can you use an oscilloscope for checking the voltages?

  • Can you remove the ferrite beads one by one and then check exactly which net is giving issue? Then replace that bead with a zero ohm resistor and then check if you are seeing the same issue? Check if that net is connected to the 1.8V VDD_INTERFACE and drawing current from there.

    Instead of using a multimeter, can you use an oscilloscope for checking the voltages?

  • Yes, as told earlier, we had removed all the ferrite beads at 1P3_SUPPLY_B and found that it is ok when we remove FB19 & FB20.

    These two nets 1P3_TXA  & VDDA_RX_TX are not connected to 1.8V VDD_INTERFACE, we had removed 1.8V supply to be sure. And yes, we had used oscilloscope as well, there are no oscillations at both these nets.

  • What is the VDD_GPO supply  voltage? Check if any GPO is connected to 1.8V. 

    What is the issue that you are facing because of this?

  • The issue is that we are getting 1.8V on these nets instead of 1.3V. We have not programmed the device yet. What issues can we face because of this? Would it be programmable or what can be the performance issue because of this, that we should be made aware of?

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