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AD9129: Voltage at VDD pins without power supply connected?!

Question asked by mikaelis on Oct 10, 2016
Latest reply on Mar 17, 2017 by mikaelis

Dear all,

 

we recently designed a PCB comprising two AD9129 DACs, a XILINX Kintex FPGA, the required power supply and peripherals such as GPIOs, communication (USB, Ethernet, ...)

 

we manufactured multiple boards and when testing the power supply for the first time, we experienced problems with BOTH the analog and digital 1.8V power supplies (powered with two dedicated voltage regulators): VDD was at 2.4 V  and VDDA was at 1.4V.

first we believed that there was something wrong with the voltage regulators so we soldered them out of the board. but still the voltage at both power supply pins remains 2.4V (VDD) and 1.4V (VDDA).

next we took the second manufactured board to see if we experience the same behaviour: it's exactly the same. It seems that the DAC is OUTputting 2.4 / 1.4 Volts at its supply voltage connections which -of course- is not correct.

 

I checked the DAC connections in the schematics multiple times. VSSA voltage is set to -1.5V and is correct. The schematics were done according to the evaluation schematics.

As a next step i will contact the manufaturer of the PCB to check if something went wrong during the manufacturing process. I have an X-ray analysis report of all of the assembled chips including both DACs. There is nothing wrong with the soldering of the chips.

I attached some of the most important schematic screenshots just in case ... Edit: Inductor between VDD and VDDA: DNP means DoNotPopulate

 

Does anyone have an idea what we might take a look into?

Any suggestions are welcome.

 

Regards,

Mikael

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