Optimizations for Inrush current

I have a USB-powered board which draws a lot of inrush current (close to 1A) on startup. This leads to problems with the USB interface with the computer and also the voltage level droop seen by the devices on the board. Now I am faced with the task of figuring out a way to solve this problem but I have no clue over how to go about it.

The board has an FPGA, a microcontroller, SRAMs, EPROM, and plenty of discreet components. No power sequencing is done and all the regulators turn on at the same time. The board has a TPS2014 which helps limiting inrush but seems is not enough.

How do I go about optimizing the values of bypass caps to reduce inrush while maintaining their bypass function? Is there a way to simulate that? Are there other ways? Power sequencing is a bit difficult because the FPGA uses 3 supplies.

Thank you.

Reply to
M. Hamed
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What are the V & I on these 3 supplies? You should at least control one or two of them?

Reply to
linnix

The voltages are: 3.3, 2.5, 1.2.

I'm clueless about two things:

1) How to measure current drawn from each regulator?

2) How to sequence power in hardware with no software control. Would an RC delay + a transistor work?

Thanks.

Reply to
M. Hamed

I don't know if these inrush current limiters would be slow enough to remove your glitch, but worth checking out, or waiting for others to give their opinion. My only experience is replacing a smoked one in my computer power supply. Interesting devices!

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Maybe this one?

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Mike

Reply to
amdx

At GenRad I used a resistor paralleled with a TRIAC.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

[snip]

A buddy of mine was breaking my supplies (on purpose) by rapidly toggling the on/off switch, so the inrush thermistor didn't have enough time to cool. My TRIAC approach reset automatically on drop of AC.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

But Jim, that's to easy and cheap!.. can't you come up with something that breaks the budget ?

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Reply to
Jamie

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