Hi All ,

We are working on XC7A200T-1FFG1156I FPGA based design which has sequencer to power up sequence VCCint - 1V, Vccaux - 1.8V , bank Vcc0-1.8V , bank VCC0-3.3V. In one of the assembled board while checking output impedance between all supply rails , between bank vcc0-1.8v and ground it is showing 33 Ohm and between MISO pin and ground around 7 ohms. Where could be issue? is it MLCC cap issue or internal FPGA issue?

 

Hi All ,

We are working on XC7A200T-1FFG1156I FPGA based design which has sequencer to power up sequence VCCint - 1V, Vccaux - 1.8V , bank Vcc0-1.8V , bank VCC0-3.3V. In one of the assembled board while checking output impedance between all supply rails , between bank vcc0-1.8v and ground it is showing 33 Ohm and between MISO pin and ground around 7 ohms. Where could be issue? is it MLCC cap issue or internal FPGA issue?

Few things
Try the AMD / xilinx forums for people who specialise in supporting their chips.

Do not ever use a meter to measure resistance on a board with modern chips .. these chips are remarkably susceptable to damage by reverse currents / over voltage . As no power applied , the max voltage is fractions of a volt , check the data sheets.

Each and every logic pin on the device will have inherant diodes to ground and power . Your probably forward biasing these diodes

Also on an assembled board , if you try to measure power rail to ground resistance , your measuring everything , including the capacitors and the power supply . Probably a silicon device .
Qed.
Measuring board resistances in potentially deadly to the board, depending on the capabilities of the test equipment and polarity of the leads .
At best tells you nothing ,worst it tells you lies

Why are you trying to destroy your board ?
What's the aim of this ?