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Observer ccthx1138
Observer
2,256 Views
Registered: ‎04-27-2017

Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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Hi guys.  New here.  I'm about to fire up my first PCB design with FPGA - Spartan3AN.  It's finally lunch day. 

I thought i better ask those who know, or can surmise, if i should ramp the current up from my test bench supply (5Vdc) to the PCB, or set the current to limit just over expected current (375mA quiescent on 1.2V, + a few mA for 3.3v and peripheral ICs),  so about ~400mA and apply full power instantly?  Other considerations?  TIA.

 

Cheers,

 

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Scholar austin
Scholar
4,133 Views
Registered: ‎02-27-2008

Re: Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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c,

 

Set current limit as you suggest.  Power on must not be slower than 50 ms (10% to 90%), and not as fast as below a millisecond or so (all devices are tested to these limits).

 

If you get higher current, check for assembly shorts, solder splashes.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
4 Replies
Scholar austin
Scholar
4,134 Views
Registered: ‎02-27-2008

Re: Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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c,

 

Set current limit as you suggest.  Power on must not be slower than 50 ms (10% to 90%), and not as fast as below a millisecond or so (all devices are tested to these limits).

 

If you get higher current, check for assembly shorts, solder splashes.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
Observer ccthx1138
Observer
2,242 Views
Registered: ‎04-27-2017

Re: Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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Hi Austin.  That's great.  Thanks for your help.  So, current-limit, instant-on it is.

 

I'm not sure how fast my bench supply reaches voltage on pressing the power supply 'output' SW. 

But I understand the tight constraints on dV/dT are for successful FPGA start-up, and not a constraint that must be met to prevent damage to the IC, is that correct? 

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Scholar austin
Scholar
2,239 Views
Registered: ‎02-27-2008

Re: Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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Correct,

 

Only way to damage is to exceed the absolute maximum limits in Table 1 of the data sheet.

 

Or zap it with ESD.

 

I suspect you know how to prevent that.

 

 

Austin Lesea
Principal Engineer
Xilinx San Jose
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Observer ccthx1138
Observer
2,236 Views
Registered: ‎04-27-2017

Re: Powering up first ever FPGA based PCB - Spartan3AN - ramp up current manually?

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Good to know.  Thanks, austin.

 

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