LPC1768 getting hot

22 Jan 2011

Hi, has anyone noticed that LPC1768 IC is getting pretty warm with only minutes of usage of the ethernet capability. I have only connected the RD, TD lines and the mbed is not driving any other component. Is it normal.

22 Jan 2011


I used an mbed with my final project at college; The project included the lwip mbed server. I definitely remember the LCP1768 getting warm, but not hot. Then again we were running a lot of other external components as well.

- Andrew

22 Jan 2011

Mostly the warming above usual is due to outputs usage. The dissipated heat is related to dissipated power.

23 Jan 2011

Yes, but there are no peripherals connected. I wonder how much current PHY is drawing. LPC1768 is getting pretty warm quickly, and therefore i am reluctant to go any further.

23 Jan 2011

Take a look at http://mbed.org/users/no2chem/notebook/mbed-power-controlconsumption/

Indeed the PHY takes up quite a bit of power and you can disable it with the code from the above link. Also my LPC1768 can get fairly warm too.

24 Jan 2011

If you *are* using the PHY permanently, then disabling it isn't exactly an option, right?

Well, the warmth is probably the sum of the PHY and the lpc1768, which in most scenarios runs at 100mhz in a tight, idle loop. This tends to dissipate a great amount of power.

An option would be to make your program mostly interrupt driven and make the cpu go idle on the main loop. Perhaps the MAC and/or the PHY also has a low power mode.