More power/heat related problems ...

I think I found another problem I didn't notice before.

I have the R-pi hooked up in the prototyping gig I described on another thread (http://www.element14.com/community/thread/18981?tstart=0),

currently no keyboard, HDMI monitor, just network and access to console via the serial port.

I've been running a trend plot monitoring the +5V feed to the R-pi and the output of the 3.3V on board regulator. I noticed that gradually

the voltage out of the regulator has increased from 3.30V to almost 3.39V, it is actually not doing much, just responding to ping packtes

(flood mode) I'm sending from another machine and serving the serial console I use once in a while to run procinfo and network stats.

I guess the voltage increase is probably not noticeable when there is more load and current draw, the only thing I can think of is self

heating of the LDO. I just placed one of the little heatsinks I've got for the LAN9512 on the LDO and seems that output voltage is starting

to slowly drop. I'll keep this configuration to see if with the heatsink the voltage keeps droping.

-J

Parents

Former Member over 13 years ago

Looking at a data sheet the top end spec for a LDO1117 type device should be 3.333V and reduces with increased temperature. Heatsinking isn't going to hurt though. I take it that there is nothing connected across from your external psu that would influence things?
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel
jamodio over 13 years ago in reply to Former Member

Nope, nothing from the external supply, I'm not using a USB psu, it is a direct 5V fee to P1 from a DC-DC converter powered by a bench ps.

I removed the heatsink and stuck a temperature probe on the tab of RG2, and restarted the trend plot. The output of RG2 is showing now about 3.36V
and temperature is about 40C (ambient is about 27C).

It is not a big deal because we are still within spec, and it could have been a measurement anomaly, particularly with LDOs you can have some
variance when the rest of the circuit draws more or less current. I noticed that with the keyboard and HDMI connected the output of RG1 is
slighlty lower, I have no means how to measure the current draw out of it.

Another test I'm thinking of is to remove RG2 and feed the 3.3V with an external ps to P1 via and ampmeter and get some baseline current draw
profile with the R-pi doing different things and stuff like the HDMI monitor connected or not.

I've no clue if anybody at RPF did this kind of tests or not. Is there any record or discussions when the board was on the early design phase ?

-J
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel

Reply

jamodio over 13 years ago in reply to Former Member

Nope, nothing from the external supply, I'm not using a USB psu, it is a direct 5V fee to P1 from a DC-DC converter powered by a bench ps.

I removed the heatsink and stuck a temperature probe on the tab of RG2, and restarted the trend plot. The output of RG2 is showing now about 3.36V
and temperature is about 40C (ambient is about 27C).

It is not a big deal because we are still within spec, and it could have been a measurement anomaly, particularly with LDOs you can have some
variance when the rest of the circuit draws more or less current. I noticed that with the keyboard and HDMI connected the output of RG1 is
slighlty lower, I have no means how to measure the current draw out of it.

Another test I'm thinking of is to remove RG2 and feed the 3.3V with an external ps to P1 via and ampmeter and get some baseline current draw
profile with the R-pi doing different things and stuff like the HDMI monitor connected or not.

I've no clue if anybody at RPF did this kind of tests or not. Is there any record or discussions when the board was on the early design phase ?

-J
Cancel
Vote Up 0 Vote Down

Sign in to reply

Cancel

Children

No Data