USB DP Module gets too hot

I have a FEZ Spider connected to a 4.3" TFT display module (T43). As per the specs of the USB DP module, I am using a 12V, 2000 mA adapter. When I plug in the adapter, after a while, the USB DP module becomes very hot (about 10 mins). I have to disconnect it as I’m afraid it might damage the other components.

Interesting thing is that when I simply use the USB cable for power, everything works normally and the DP module heats up very little.

I saw this thread and it seems others have this issue too.

Any suggestions on what could be wrong is welcome.

The DP power module iisa linear regulator. That means that if you take say 200mA from the 3v3 rail you will also take 200mA from the 12v rail. The regulator has to dissipate the energy caused by the voltage drop (12v-3.3=8.7v : 8.7v * .2A=1.74Watts). I.e when running at 12v the regulator is consuming over 3.5 times the power of the Spider.

If you can drop the power down closer to the 7v minimum of the DP module you will see it run much cooler. That said it should be designed to survive the heat.

@ hagster - USB DP module has two voltage regulators. It drops input voltage (12V in this case) to 5V using switch-mode voltage regulator and then it drops those 5V to 3V3 using linear voltage regulator.

@ iamin I have just picked up my board and checked and you are correct.

@ vishnusharmaNewbie Can you confirm it is the DP module and not the new EDP module. The EDP has a micro-USB and no inductor on the board. The DP has a micro-USB and a switch-mode 1st stage regulator.

@ hagster I have the old DP module and not the EDP module. The module I purchased is here

I did think through the voltage difference. To check, I created a 9V power supply using LM7809. I plugged in the 12V, 2A adapter to the input of the 9V power supply.
Then I connected the 9V power supply output to the DP module.

In this setup, the DP module heating issue was reduced, but my 9V power supply started to get hot a lot.

Now this is confusing me more.

In this setup, the DP module heating issue was reduced, but my 9V power supply started to get hot a lot.
Can you measure how much current your USB DP is now drawing when being fed from the 9V source?

I am reminded of how hot an old laptop PSU got when the lead that ran to the laptop developed a minor short-circuit due to continuous coiling and uncoiling when packed away. It wasn’t enough to cause the PSU to fail, but the extra current that was drawn raised the temp of the PSU to probably 40+ degrees.

Could it be that there is a high(ish) resistance across the output of the USB DP that is drawing much more current than that being needed by your Gadgeteer board? I don’t have any of my Gadgeteer stuff with me until Monday, but I’ll measure a couple of USB DPs I have to see how much current they demand when unloaded and again when a Cerberus is plugged in idle.

@ Jason thanks for your help.
I made provision to measure the current in my own 9V power supply.
The input to my power supply is 12V, 2000 mA power adapter. The output is 9V, 1000mA (max rated)(using LM7809).
The output is connected to the USB DP module’s barrel jack. In this configuration, the FEZ Spider is connected to 4.3" TFT LCD.

I took 10 measurements and on an average, the current measured was in the range 320 mA to 370 mA. Once in a while it will shoot to 400 mA but only in two such measurements it happened.

This means, it I take the upper values too, the current consumption is about 400 mA. With a 12V input (my original configuration) and a 5V output (I saw the schematic for the DP module) there is a 7V drop across the 5V regulator. Therefore 7 * 0.4 = 2.8 W.

Is 2.8 W that hot? I’m not sure. The DP module is too hot to even touch (though the red LED does not flash indicating overheating).

Those currents sound about right for the output to your Spider board and LCD. As this should be a switched mode they should be much lower at the input to the DP module.

Can you check the output current? If it’s similar then you have a faulty DP module.

I have checked the current from the output of the DP module and they are similar…around 350mA. Based on what you are saying, I guess I have a faulty module :’(

@ vishnusharma - If you believe that you have a faulty module, you can contact us directly for an RMA.