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AD9364/AD9363 power supply problem

Category: Hardware
Product Number: AD9363/AD9364

Hello,

 We designed a transceiver board with both AD9363 and AD9364 transceiver chips. Currently, we are facing 1.3V power supply problem with both AD9363 and AD9363.

In the attachment, RX line-up, LDOs and power supply schematics are provided as a reference. AD9363 and AD9364 chips are supplied with different LDOs and pin-out of both chips are exactly same schematics. For each chip, two different LDOs are used for A(analog) and B(digital) supply pins of the chips as recommended in user guide. A supply is used for analog pins and B supply used for digital pins. External 1.8V signal is converted to 1.3V signal by these LDOs(ADP1755). 70MHZ 1.3Vp-p sine wave is used as reference clock signal for both chips.

As a result of unknown reason,  9363_+1V_SUPPLY_A and 9364_+1V_SUPPLY_A nets became short circuited. On the other hand, 9363_+1V_SUPPLY_B and 9364_+1V_SUPPLY_B nets are working properly. When we removed R3 and R18(output of A port LDOs), LDO output become open and short circuit remains at A supply pins of both chips. And we realize that these A supply ports are related with RF components such as VCO, LO and synthesizer etc. of the transceivers.

Is there any possibility of any signal or high voltage reaches to RX or external reference ports of both chips and as a result of protection mode of chips, the current flows into supply pins instead of ground? Or any other unwanted signal effects supply pins and makes them short circuited? 

We have faced this problem with twice out of 40 boards. These 2 problematic boards were previously worked fine. For unknown reason, this problem occurred.

Is there any solution for this problem?

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