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Registered: ‎07-18-2019

XC9572XL freezing from time to time

I have XC9572XL in my application (3 phase inverter). The CPLD takes in the input pulses from the control circuit and passes them to the mosfet drivers (Si8271GB-IS). The „program“ in the CPLD is very simple in the moment. A buffer between the input and output pins. Nothing else. The pulse frequency is 36 kHz, CLK runs at 50 MHz.


The problem is the following: When I increase the voltage on the inverter DC bus (nominal is 48V), above aprox. 24 V the CPLD freezes sometimes. The input pulses run, the clock is supplied, but there are no outputs. A reset helps.


I have tried the following:

  • Measure voltage on the CPLD power pins => no voltage spikes
  • Fitted ESD protection (transil ESD5Z2.5T1G, actual cutoff voltage about 4.4 V) to cut off eventual voltage spikes on inputs and outputs. This helped a little bit. I was able to increase the voltage on the DC bus to about 32V
  • Changed the CPLD “program” from asynchronous to synchronous design. An FD flip-flip on each input, clk from oscillator, output to the driver. This helped so that now the DC bus voltage is 48V.


Still, from time to time, every few minutes, the CPLD “freezes”. I suppose this is some EMC issue.


Any ideas:

  • How the CPLD can actually freeze?
  • How this could be diagnosed and suppressed?


Thank you



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Xilinx Employee
Xilinx Employee
Registered: ‎03-07-2018

Re: XC9572XL freezing from time to time

Hello @martin.movak2 

How you are connecting CPLD signals to MOSFET drivers? Is there is any isolation?

If your high power system ground are common with CPLD and control circuit, it will surely introduce noise in your CPLD and control circuit. Eventually it will cause failing their operation. You can check noise on ground pin and CPLD clock pins using oscilloscope while increasing voltage on DC bus. (Warning: Be careful while handling oscilloscope on such system, it can damage your oscilloscope if probes used for measurement are incorrect or wrong test points are connected. This can also hurt you if proper precautions are not followed.)

I will recommend to use opto isolation between cpld and power mosfet in such case. This may resolve your issue.


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