Battery Shield Charge Current Resistors are Incorrect (and risk battery fire)
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Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 25/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Stale
- Domain
- embedded-iot
Research direction
Start with the TP5400 datasheet and the linked CE forum post to verify the resistor calculations and the shield's documented jumper behavior. Determine where the battery shield's charge-current resistor values are documented, then update the affected hardware documentation so the stated 0.5A and 1.0A settings match the supported limits.
Written by the indexing model from the issue text.
Description
The charge current selection jumper on the battery shield should select between 1.0A and 0.5A charge current according to the documentation. However, I've just checked the datasheet for the TP5400 charge IC - your shield is wrong.
The 0.5A default setting will output around 0.8A, and shorting the jumper actually sets it to 1.6A not 1.0A!
See my post on the CE forums for full details:
https://forum.core-electronics.com.au/t/polymer-lithium-ion-battery-400mah-ce04375/298/18?u=oliver33
In summary; from the datasheet for the TP5400:
RPROG = 1100 / IBatt
The charge resistors on this shield are 2x 680 Ohm in series. Open jumper gives:
RPROG = 1360 =>
IBatt = 1100 / 1360
IBatt = ~0.8A
Closed jumper gives:
IBatt = 1100 / 680
IBatt = ~1.6A
Which is greater than the absolute max of 1.2A the TP5400 is rated for.
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- 36
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