Reducing the heat generated by the board

[jlumme]

We're trying to think of ways to reduce heat generated by our custom board, and so far we have done the following:

• Reduce the CPU speed by half (227MHz)
• Force USB to 1.1 mode
• Force USB WLAN to 1MBit/s speed
• Enable power saving on USB WLAN (I somewhat doubt this helps)
• Lower DDR clock slightly

With these modifications the average board temperature was lowered by approximately 4 degrees, and I wonder what else could I try to lower the temperature generation further. I am assuming the lowering of CPU clock was the biggest win here.
I'm planning to test gating off Audio (SPDIF)  since we don't need it, but would appreciate any additional ideas..

[progmetalbg]

Lowering CPU core voltage could also help
http://cache.freescale.com/files/dsp/doc/app_note/AN4050.pdf

[jlumme]

Hmm, that's a good idea. If I recall correctly, currently VDDD is at 1.5v (default by uboot for mx28 and mx23) - maybe I could try lowering it a bit and see if I have any instability issues (I remember playing around with it when we had some [unrelated] boot issues in previous designs but we had some stability problems).. Thanks for the suggestion!

[t35tB0t]

Just a thought here - Have you explored using the low-power operation modes?  (section 12.2.6 of the imx23 RM)?  QUOTE: In many applications, it is desirable to minimize the power consumption of the memory controller and the memory devices. The memory controller provides various user-configurable low-power options to address power savings. In addition, a partial-array self-refresh option is included for mobile memory devices.

Changing to a mobile DDR memory may also have a significant impact but I suspect that's a bit more difficult to implement.