CMOD A735T High Current Consumption

[MTIabhishek]

I purchased two CMOD A735T parts and they both ended up having the same issue. The parts worked fine connecting to a PC, and programming, etc. Over the period of 1 week evaluating them, they seem to be getting hotter and hotter, and one eventually stopped responding, and the second unit's LEDs stopped working. We measured the current consumption on the USB, which was ~2A. Is this a known problem with these boards or is there any heatsinks needed on the board for thermal management? I have seen other forums talk about current consumption in the few hundred milli-Amp range, not 2 Amps, which is above the spec for USB 3.0 ports anyway. We checked the board for any shorts on the USB connector, USB FIFO chip, etc but no shorts anywhere.

Anyone else see this issue or recommend any steps to  troubleshoot? Two different modules had the same issues, after testing on different machines, using various different USB micro cables, etc to eliminate non Digilent part issues.

[Gra]

Hi MTlabhishek,

 

I took a really quick look at the schematic, looks like the max power out on that converter is a little under 5W, so you shouldn't be seeing 2 amps in at 5V.

I'd start by re-loading a reference design and measure the current again. Your design can change the power drawn, design errors can also cause large currents to flow.

Gra

 

[jpeyron]

Hi @MTIabhishek,

How and where are you measuring the current? Please attach your block design/HDL code, wrapper and xdc file.  Are you able to see either or both of the  Cmod A7's in the Device Manager?

thank you,

Jon

[MTIabhishek]

Quote

 

we are measuring the current at the USB between the port on the computer and the USB micro connector on the CMOD A7. We are using the ADC sample project provided by Digilent - no changes yet to the code.

[jpeyron]

Hi @MTIabhishek,

Could you use a DMM and measure voltages of few different capacitors:

C80  should be 1.0 v

C82  should be 1.8 v

C84 should be 3.3 v

C18 should be 3.3 v

C29 should be 3.3 v

C41 should be 3.3 v

C54 should be 3.3 v

Are you able to see either or both of the  Cmod A7's in the Device Manager?

Are you able to see either or both of the Cmod A7 in Adept 2 here?

The XC7A35T-1CPG236C is commercial grade for its operational Temperature Range which is 0°C to +85°C. Is the FPGA getting hot enough to burn you on touch( 85°C)? 

Also to clarify are you powering the Cmod A7 through the usb or externally through pins 24 and 25 as described in the reference manual in section 1.1 Power Input Options?

thank you,

Jon

[MTIabhishek]

The FPGA is getting hot, but the hottest component was the USB FIFO chip. After some microscope inspections and probing, we measured the power supply chip and the capacitors you mentioned. The feedback node is messed up on the 1V supply (between C80, R66, R65 and C79). The VCC1V0 was putting out 1.5V. Not sure how this happened, but we purchased a third unit and are watching the voltages carefully as we test / debug.

[jpeyron]

Hi @MTIabhishek,

So that we have a better understanding of the issue:

Also to clarify are you powering the Cmod A7 through the usb or externally through pins 24 and 25 as described in the reference manual in section 1.1 Power Input Options?

Are you able to see either or both of the Cmod A7 in Adept 2 here?

What voltages were you using with the XADC project?

thank you,

Jon