Power FAQ

What is the highest voltage stargate will work with? I have a 7.2V battery and I'm wondering if I can use it with stargate.

Theoretically, the on-board +5V regulator can take the input from 4V to 12V but the more input voltage; the regulator generates the more heat. The typical range is +5V to +7V. The Stargate still works from +7V to +9V but you can feel the heat at the regulator U7 since there's no heatsink installed. It also depends on the work load.

Give the above, I would be careful. When we use a 7.2V battery on the Stayton, we send it through a 5V 2A external regulator attached to a heat sink with silicon grease. We did this in part because we had a heavy load: a PCMCIA serial card, PCMCIA 802.11 card, and USB web cam. (Remember, an external regulator costs much less than a Stargate.)

What is the effect of switching the jumper (J8) from Jack to battery power?

J8 chooses the type of power source: In Positions.....

  1. Battery on main board provides power to a 3.3V regulator on the main board, and onto the electronics on the main board. It will also power the daughter card (if present) but no +5V will be available for the USB Master connector; Ethernet and Serial will work fine. This assumes you are not also connecting power to the DC jack on the daughter card - if you are, it will only provide +5 regulated on the daughter card to the USB master, everything else will still be powered from the battery.
  2. Battery disconnected. Power derived from daughter card [DC jack input, +5volt regulated on daughter card]. This supply is further regulated on the main board with a 3.3V regulator, which is also fed back to the daughter card and powers the 3.3V chips on that board.

If you use the Stargate main board alone (without the daughter board - this is the case for our Personal Server model) then you want to run it from the battery connected to the main board J23. In this case, you must jumper J8 to battery position.

If you use both the main board and the daughter board together, this is the case most people do, then you leave the J8 jumper to the JACK position. Both boards will be powered from the Jack input J49 or from the battery connected to J7 on the daughter board.

What maximum current supply can a USB-client expect from the USB-host adapter on the daughter card of the Stargate?

We designed the USB 5V connector with a 1A 5V regulator. 500mA is well within its capability. But main issue is the power dissipation in the regulator = (Vsupply-5V)*500mA. The regulator has NO heatsink, and it WILL get hot and overheat if it needs to drop too much potential across it. If you feed in exactly 5V from a regulated source, 500mA should be fine. However if you are using an unregulated power brick, you might be a volt or two over and this will result in excess heating. So it does depend on the way it is used. We have tried mounting a heat-sink on the regulator (coupled with silicon grease) to deal with higher dissipations, and it did work, so you could do some tests and provide your customers with an application note for work with high current loads.

How much current does the Stargate draw?

Jaidev, here are some power numbers. All are measured at 4.5V, so they will probably be a little bit less in practice.

Multiply by 4.5 to get the power consumption.

all These measurements are with the Daughtercard in and ethernet enabled. It will be quite a bit less without those two. The sleep current is a lot higher than it should be, so this is under investigation...

I looked at the Power FAQ, and there are some numbers for current drained by Stargate. I was wondering how this numbers were obtained, I mean where in the circuit this current was measured.

I used an HP power source to power the Stargate (which also gives me the current being drained), and I my initial results were different (idle=130mA, idle+wifi=290mA, idle+webcam=300mA). I will do my measurements again, but I was wondering if I have a different setup...

What is the reason for choosing 4.5 v? Is this the input voltage on the daughter card power jack? If so, shouldn't it be at least 5v?

The system only really need 4.5V to run -- and I think that's what the batteries suppy. All the main subsystems on the board are regulated down to 3.3v. Only some of the USB things might take 5V, but I didn't have any of those attached.

What kind of battery does the Stargate work with? Does the battery power both the processor and daughter boards?

If we are powering the motherboard only (no daughter board), we use a


We have also used the following combination (thanks to Illah Nourbakhsh CMU).

Does anyone have advice about battery powered stargates? We only require a short supply (a few hours).

John, we typically see a battery life of 3+ hours with a fairly small (900 mAh) battery... This will be quite a bit less depending on the PCMCIA cards you have. Are you planning on using WiFi or other cards? (Other than straight-up flash, which is very low power).

We are using a back-up of 4 D size cells for the stargate enclosures we are building for the Fab App project. The idea is to provide a backup during AC power loss. It would last upto 72 hours while CPU is idling.

We are powering stargates from (rather large) car batteries. Our seismic enclosure includes a DC-DC converter to take the voltage from 12 down to 5. (It's part of an interface board which is mostly connectors but also has this one chip on it.)


Is the power monitor a function internal to the X-scale processor or is this a module of a specific external chipset?

There is a specific componnent on the board that is supplying this function. It's a DS2438 -- I've attached the datasheet.