I'm designing a new board based on XC6SLX9-3TQG144C. There are three supplies required — VCCINT, VCCAUX, and VCCO. VCCINT is 1.2V and the other two will be 3.3V. I'm wondering how much current to design for in the power supplies. Obviously the current consumption depends significantly on the RTL running inside, but are there any good rules of thumb for this? In the past I've just over designed the thing to be able to supply something like 1 amp (can't remember which LDO I used, but at the time it was a national part) for the internal supplies and whatever I think I'll need on the I/O side of things (which is much easier to estimate). I'm trying to minimize area on this board though so it would be nice to not just "shoot the fly with a bazooka" so to speak. Is there a reasonable way to accurately estimate the current consumption for the internal supplies of an FPGA? I've looked a bit at xpower, but I didn't see (didn't spend a ton of time looking) a way to enable/disable various portions of the design as one would expect in real life (e.g. memory controllers, actions responding to external events, etc).
Electronic – How much current would you design for the various supplies required for Spartan 6 LX9 devices
fpgapowerpower supply
Related Solutions
About the worst case current draw I have seen from a higher-end micro controller is about ~200 to 300 mA. This was the LPC2388 (ARM7, 32-bits) with the usb, emc, and all the more power hungry peripherals turned on running at the highest clock speed (288MHz internal PLL divided down to 72MHz). Generally, I would highly recommend going to switching regulators if cost, noise, and complexity is not an issue.
This is a bit complex. Basically, there are a number of limiting factors:
The IO lines from the microcontroller (i.e. the analog and digital pins) have both an aggregate (e.g. total) current limit, and an per-pin limit:
From the ATmega328P datasheet.
However, depending on how you define the Arduino "Pins", this is not the entire story.
The 5V pin of the arduino is not connected through the microcontroller. As such, it can source significantly more power. When you are powering your arduino from USB, the USB interface limits your total power consumption to 500 mA. This is shared with the devices on the arduino board, so the available power will be somewhat less.
When you are using an external power supply, through the barrel power connector, you are limited by the local 5V regulator, which is rated for a maximum of 1 Amp. However, this it also thermally limited, meaning that as you draw power, the regulator will heat up. When it overheats, it will shut down temporarily.
The 3.3V regulated output is able to supply 150 mA max, which is the limit of the 3.3V regulator.
In Summary
- The absolute maximum for any single IO pin is 40 mA (this is the maximum. You should never actually pull a full 40 mA from a pin. Basically, it's the threshold at which Atmel can no longer guarantee the chip won't be damaged. You should always ensure you're safely below this current limit.)
- The total current from all the IO pins together is 200 mA max
- The 5V output pin is good for ~400 mA on USB, ~900 mA when using an external power adapter
- The 900 mA is for an adapter that provides ~7V. As the adapter voltage increases, the amount of heat the regulator has to deal with also increases, so the maximum current will drop as the voltage increases. This is called thermal limiting
- The 3.3V output is capable of supplying 150 mA.
- Note - Any power drawn from the 3.3V rail has to go through the 5V rail. Therefore, if you have a 100 mA device on the 3.3V output, you need to also count it against the 5V total current.
Note: This does not apply to the Arduino Due, and there are likely some differences for the Arduino Mega. It is likely generally true for any Arduino based off the ATmega328 microcontroller.
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Best Answer
The answers above seem to suggest that the datasheets provide sufficient information to determine the power consumption of the device. I disagree -- The datasheets provide a lot of information on quiescent current, leakage currents, etc, but they cannot speak to dynamic power consumption, which accounts for the vast majority of the power used. After all the datasheet has no idea how fast anything is switching the device, how much of the device is being utilized at any given time, or what peripherals (e.g. serdes/memory controller stuff) are being used at any given time.
After digging into this a bit more it's not too painful to dump a vcd file to xpower and get a fairly reasonable estimate for power consumed by the various supplies. Ultimately though it seems that for 99% of the cases over designing the supplies by some reasonable amount of headroom is easy enough and probably not worth optimizing a ton.