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dpenev
Beginner
966 Views

How to bring up FPGA board with short in the power rails.

Hello,

 

I am trying to bring up few new prototypes using Stratix IV FPGA (EP4SGX70HF35C3N )

One of board is working fine.

 

I have trouble switch the other one. Almost all power rails going to the FPGA are shorted to the digital ground (GND)

The PCB house and the assembly a top class so this is very strange. 

Attached is a diagram with the shorts to GND I have measured.  

Only +1.1V, VCCA_R/L and +1.5V (if the ferrite beads is unsoldered) are not shorted. 

All the rest is shorted. We have JTAG connected to the FPGA. 

 

If the board is powered from the power supply with current limiter increasing the current the DC-DC regulators on the board for 

2.5V, 1.8V, 0.9V and 1.5V start heating. 

 

Any ideas how the issue can be narrowed down?

 

Thanks

Dimitar

0 Kudos
5 Replies
AnandRaj_S_Intel
Employee
58 Views

Hi,

 

Debug steps

 

Check board for Solder Bridging (Specially near all power, ground pins).

 

Method -1

Force current and measure voltage(FCMV) which will help in finding the short.(source-measurement unit /Parametric-measurement unit/multimeter with high Resolution.

 

Method-2

You apply power, and look for a temperature rise on a specific component. It works quite well.

 

Method-3

Removing components.

  1. List down the components on power rails(Regulators and passive components) try to suspect the component.(In my view i will suspect the 2.5V, 1.8V, 0.9V and 1.5V start heating DC-DC regulators->passive components ->FPGA)
  2. If possible can we desolder the regulator and check.If short persist,
  3. Try to do same for passive components on regulators and FPGA side.

 

Let me know if this has helped resolve the issue you are facing or if you need any further assistance.

 

Best Regards,

Anand Raj Shankar

(This message was posted on behalf of Intel Corporation)

dpenev
Beginner
58 Views

Hi Anand,

 

Thank you for the message. What I have done so far:

 

Method -1. I have used Kelvin probe and the smallest resistance was detected below the FPGA on few decoupling capacitors .

it seems something like 10 mohm. (the ohm-meter has been zero with probes shorted)

 

Method -2 We have far end infrared camera and we are using regularly for this kind of issues.

The problem with this is that if we have +V ---resistor ---- short ---- GND the resistor is heating not the short.

In this particular case the main suspect so far is the FPGA (component or the soldering). The FPGA is heating a bit but not much.

if we apply 10Watts of the power input of this board I think something like 1, 2 Watts is dissipated by the FPGA the rest is dissipated mostly by the DC-DC regulators on this board (mainly +2.5V, +0.9V, +1.5V). Those heat a lot. At this point we have voltages on the rails like this :

+2.5V - 0.3V

+0.9V - 0.1V

+1.5V - 0.1V

Method - 3 Yes we have removed some of the components for the DC-DC regulators. Still short in the power rails. This is pretty big board and there are lot of the components.

 

 

I think we will try to use Method 1 a bit more and probably the next step is to un-solder the FPGA.

Any ideas will be greatly appreciated!

 

Best Regards

Dimitar

RPDM
New Contributor I
58 Views

I guess you've checked that the FPGA hasn't been placed wrongly? I.e. rotated?

dpenev
Beginner
58 Views

Hi Like,

 

Yes this has been done, and the chip is not rotated.

 

Thank you

Dimitar

Rahul_S_Intel1
Employee
58 Views

Hi Dimitar,

May I request to check the FPGA is gone bad.

Regards,

RS

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