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Topic: Voltage Issues (Read 713 times) previous topic - next topic

aziandude1

Thanks for the replies. I'll do both for sure. At least the Li-Po cell I'm using has a protection PCB to prevent it from over discharging, and hopefully I didn't damage the microcontroller with this design flaw...

retrolefty

I agree, do both as using just a resistor still allows the li-po cell to discharge (even at low current) the cell below the value where permanent damage can result to the cell. Over discharging and charging are the two easiest ways to destroy a Li-po battery cell.

Lefty

MarkT

Yes, do both, and make it perhaps more, 4k7 or 10k.  Analog inputs are happy with upto 10k impedance signal (get less accurate as you rise to higher impedances)

You have already possibly damaged the protection diode or nearby stuff on the chip, so don't be surprised if its misbehaving, but you might be lucky.

General rule is never apply low impedance signal to the inputs of a powered-down chip - you can put the chip into latch-up as well which means when the power is applied it overheats and doesn't work till all power is removed.  Series resistors on logic inputs will marginally slow down the rise/fall times but will protect the chip from damage and latch-up.


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aziandude1

#4
Mar 03, 2012, 07:25 pm Last Edit: Mar 03, 2012, 09:03 pm by aziandude1 Reason: 1
So just to make sure I understand correctly. I should put at least a 1K resistor between the I/O pin used to read the battery voltage and the battery to prevent the protection diode from getting forward-biased when the system is off. I just want to make sure because its a custom PCB and I'm going to have to cut the trace to add the resistor.

As another solution, could I just reroute the analog I/O trace to the opposite side of the power switch so that it only gets the battery voltage when the system it turned on? 

Magician

You better add up serial resistor as suggested above, and also connect this resistor after the switch - to prevent you battery from over-discharging.

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