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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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  • Please verify the impedance of the pins which is supplying _A nets in off conditions by removing the resistors R3 & R18, and also compare with a good working board. 

    And also verify the layout if any of the power supply trace nearer to the ground caused the grounding. You mentioned that these two boards were working initially and for some unknown reasons now it shows short, do you remember what kind of tests were performed, this is just to know if any test case caused to overflow the current and caused damage to become short.

  • Hi RR4,

    Thanks for your reply.

    After removing the R3 and R18 resistors, 9364_A net impedance is calculated as 15ohm and 9364_A net impedance is calculated as 60 ohm. For good working board, these impedances are both 18kohm. Also, I verified the supply traces and it looks ok. This short circuit problem is occurred when performing RSSI gain step calibration test.

  • were you able to measure the impedance of A nets of the device, whereas here you mentioned calculated impedance, do you mean is it measured with DMM? did you isolate all other connections of pins which 9364_A pins powered? 

    15 ohm and 60 ohms indicate that there is a low impedance path formed maybe it is due to power planes short or some other, can you please verify this?

  • Hi RR4,

    I am very sorry, I expressed it wrong. I mean that the impedances are measured with DMM. When measuring, other 9364_A pins cannot be isolated because there is direct connection between all 9364_A supply pins as shown in the schematics. So, there is no bead or resistance to remove for isolating them from each other.
    Also, I checked power planes and they look ok.

  • you mentioned that this particular board was working earlier and in between for some reason stopped working. did you observe any high current draw before it is gone bad?

  • Yes, this board is working previously. After performing RSSI calibration test, we turn off the power supply. After that, the board could not turn on again because of the short circuit problem mentioned above. During this calibration test, we did not observe any high current draw.

  • As per the problem described above and debug results indicates that it is likely that the device might have gone bad or power planes get short under the device, is it possible to do an x-ray inspection of the device and see if any short circuit under the device.

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