MityDSP-L138 processor running hot
Added by Ed Smith over 10 years ago
We are some way into the development of using the MityDSP-L138 platform. I recently noticed that about 50% of the time when the module is powered up the OMAP processor runs very hot, >50C. The other 50% of the time it runs relatively cool. When it runs hot the power supply on the card falls to 3.15V even though it is at 3.3V on the baseboard. When not running hot the card voltage is 3.3V, same as the base baseboard. There must be a heavy current draw to cause the volt drop and the excess heat.
This seems to be determined at the point power is applied and not later in the boot sequence so I assume it is a physical problem. In both cases the software is not affected and runs on quite happily.
Replies (9)
RE: MityDSP-L138 processor running hot - Added by Michael Williamson over 10 years ago
Hi Ed,
Are you running on a DevKit or on a custom board? Would you be willing to share your schematic (privately to CL, not via this forum page)? Are you using an FDGA variant or processor only variant of the module?
-Mike
RE: MityDSP-L138 processor running hot - Added by Ed Smith over 10 years ago
We are using a baseboard developed for our application. I'm happy to share the schematic. Let me know how to get that to you. The variant we are running is without the FPGA.
I have managed to measure the excess current draw. When it is running normally there is around 200mA less supply current.
Ed
RE: MityDSP-L138 processor running hot - Added by Michael Williamson over 10 years ago
Ok.
I suspect the issue may be related to I/O voltage levels (you have I/Os being driven or pulled to a value larger than the bank voltage), or during reset the OMAP-L138 typically pulls most of it's I/O pins (internally) to +VDD of whatever bank you are on. Could that be causing problems?
-Mike
RE: MityDSP-L138 processor running hot - Added by Ed Smith over 10 years ago
All our I/O to the card is 3.3V. The OMAP processor has 3 configurable power groups which can be connected to 3.3V or 1.8V. I believe you have them all connected to 3.3V but as I don't have your circuit I cannot verify this. Could you confirm the connections for those supplies please?
Ed
RE: MityDSP-L138 processor running hot - Added by Michael Williamson over 10 years ago
On non-FPGA variants, DVDD3318_A, DVDD3318_B, and DVDD3318_C are all tied to 3.3V.
Does the issue only occur during reset, or once the unit boots it remains "hot" until another power cycle or reset cycle?
RE: MityDSP-L138 processor running hot - Added by Ed Smith over 10 years ago
It remains hot until the next power cycle. A reset cycle alone does not give an improvement.
RE: MityDSP-L138 processor running hot - Added by Michael Williamson over 10 years ago
What are you doing with unused connections on the module?
RE: MityDSP-L138 processor running hot - Added by Ed Smith over 10 years ago
I have attached a plot showing the rise of the supply on the baseboard (channel 2) and the Mity card (channel 1). As you can see there is a droop in the supply on the card. I assume there is a switch mode regulator to generate the 1.8V for the OMAP core that is coming in at that point.
| 03 Fail condtion rise times.BMP (300 KB) 03 Fail condtion rise times.BMP | Power supply rise |
RE: MityDSP-L138 processor running hot - Added by Ed Smith over 10 years ago
All unused connections are no connects.
