Heat issue

[mitch2380]

Thanks, Agent24

[adafruit_support_bill]

The assembly looks good. What meter are you using? Are the batteries fresh? Have you checked it against a known source?

[mitch2380]

Still using a Fluke 177, fresh batteries, and the meter checks good against a 9V battery and 120VAC

[adafruit_support_bill]

Sorry for the repeat question. It's hard to keep all the threads straight sometimes. I'll see if LadaAda has any thoughts on the matter.

[adafruit]

Hello! So the question is why is it drawing about 2mA? that isnt terribly high, and is a reasonable quiescent considering the resistors we added

[mitch2380]

Okay

If that and the ~205 degree operating temperature is not a problem, then I will continue on smartly. Thank you for the assistance.

[adafruit]

if its charging a smartphone, expect it to get 'damn hot'

[mitch2380]

Fair enough, I was charging a Blackberry Bold 9650. I work with electronics and electrical equipment - I don't normally see IC's getting up to 200+ degrees. Coils and transformers, sure, but IC's that hot don't seem to last too much longer after that. When I saw this little 8-pin package get up that high, I got concerned. Especially when I am using lithium batteries and they're getting really hot, too.

[lee321987]

I'm getting ~2mA (1.9mA) quiescent current too. So this okay/acceptable on a Mintyboost v3?

[adafruit_support_bill]

Yes, the boost controller itself much less than that, but with the added resistors in V3, 2 mA is about right.

[uldics]

The heat issue is a bit bigger than you think. I got the same problem with a pair (and another) of rechargeable AA batteries, used for a while, but still normal - in other applications. But here I got Mintyboost V3 chip temperature rising immediately after plugging the phone (HTC Desire) in on one pair and after half a minute on another pair of rechargeables. One pair got the chip temperature up to 98 degrees Celsius with unpleasant hissing noise, then my conscience stopped this madness. Other pair got up to some 70 degrees Celsius. That is definately too much, there is no way you can make me believe the wet finger test is good enough. Chip datasheet says it can work up to 70 degrees Celsius. So that is not good, what I have there. Batteries got only slightly warm, no more than body temperature.

Then I started to look at the datasheet. I am no expert in all this stuff, but what catched my eye, was the mode change feature of the LT1302 chip - current vs burst mode. I guess what we have here is mode hopping occurring, when the supply voltage gets dragged down by the load. And that also makes the chip very ineffective.

I did not have any such problems with LiPo battery, where voltage did not drop, but was slowly declining at the same time as the phone battery was filled up - like in some half an hour maybe 0.4V difference, not like AAs - 10 seconds and 1.75V from two batteries.

[adafruit]

you are misreading the datasheet, the operating temperature is NOT the temperature of the chip, its the temperature of the air surrounding it.
you should look at the ThetaJMAX = 125°C, qJA = 100°C/W (N8) for the temperature of THE CHIP itself

[uldics]

OK, that calms me down a little bit. The datasheet page 13 has something I can understand, though not the whole thing. The temperature has to be red between the lines somewhere. Anyway, I'm most likely not to be using my Mintyboost with AAs, but LiPo. Had drained a LiPo (2000mAh) down to ~1.8V (though the datasheet says 2V is cutoff level), got the hissing noise, and pretty sure the temperature also rising, but the LiPo protection circuit just cut it off after some seconds. I suppose it got drained even faster then. I suppose my Mintyboost is safe that way.