Re: [Gumstix-users] My Gumstix keeps resetting

[James T. <ja...@al...>]

James Tilley wrote:
> RussellMorin wrote:
>   
>> I measured the current while the stack was booting up and it fluctuated
>> between 0.35 and 0.5 amps. The voltage regulator should be able to handle
>> 1.5 amps. It made it as far as the login screen before cutting out this
>> time. Do you think adding a fan to convection cool the voltage regulator
>> might stop it from cutting out? Do I need a larger battery?
>>
>> -Russell
>>   
>>     
> Yes, it has to be thermal limiting given those numbers. The device does 
> not have the capability to deliver 1.5A in all configurations, and as 
> such will go into thermal limiting.
>
> Lets take a quick look at some more numbers, since you have given 
> current readings:
>
> Voltage drop across the regulator is 9.4V (14.4-5).
> Thermal impedance, junction to ambient is 50 degC/W (for TO-220).
> Max junction temperature 150degC
> Ambient temp 20degC
>
> (150-20)/50 = 2.6W, this is the amount of power disspated by the 
> regulator that will put the junction temp at 150degC.
>
> 2.6/9.4 = 276mA This is the amount of current that will cause 2.6W to be 
> dissipated by your regulator.
>
> So, it _IS_ thermal limiting.
>
> You can try a heatsink, but your best bet is going to be a switching 
> regulator (or drop the battery voltage as was also suggested).
>
> James
>
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Just a quick followup...

It looks like if you get a heatsink with a thermal rating of anything 
better than (ie lower than) 20degC/W, you will most likely be OK.

Or, swap out to a switching regulator... (hint, hint :))

James