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I am working on troubleshooting bunch of overheating PCBs. I found that 2 components on my charging circuit always heat-up or malfunction even after replacement.

The first problematic component is the Power management chip LTC 4085 which connects the Li-ion battery, voltage converter chip, and the wall adapter. 5V coming from the wall adapter and is passed to the LTC 4085 chip. When the charger is connected, the battery charging voltage is 4.2V from pin 14. When charging is off, the battery voltage is supplied to the converter chip. The problem with this power management chip is, I always get the wrong output on Pin14 to the battery. I have replaced the chip, cleaned up the solder pads underneath but still many failed to have the correct output (either 0V or >4.2V).

The second problematic component is the voltage converter chip TPS63001, convert 5V to 3.3V. This component always heats up. However, it has the correct output. Again, I have tried to replace the components that heat up and clean the solder pad, but the issue is still there.

I have also tried adding a noise filter capacitor on the charging cable to make sure the input voltage is steady around 5V.

Here are the schematics of the design: enter image description here

enter image description hereenter image description here


Thank you for the responses so far. I am still struggling with this issue.

Here are the link of LTC 4085 and TPS63001 datasheet:

http://cds.linear.com/docs/en/datasheet/4085fd.pdf

http://www.ti.com/lit/ds/symlink/tps63002.pdf

I have also tried the following method trying to locate the issue recently:

Increase my R11 to 100Kohms, which connected to Pin12 on U1. This reduces the battery charge current from 1.2A to 500mA. I previously found out that the recommended charge current for my battery is around 800mA. 1.2A can be too big.. However, after I switched to the 500mA settings. I still get some board to heat up.

Any input will be highly appreciated!

Thanks


One more update on the schematics..

The current board doesn't have these components( Q5 and R40 which connect to Pin 11 from the LTC 4085). Can this be a factor of heat up and malfunction issue?

enter image description here

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    \$\begingroup\$ Not bothering to try deciphering it, obviously left, right, up and down things are cut off. \$\endgroup\$ – PlasmaHH Feb 8 '18 at 21:22
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    \$\begingroup\$ that is not the schematic. ... that is part of the schematic \$\endgroup\$ – jsotola Feb 8 '18 at 21:22
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    \$\begingroup\$ Sorry guys, i posted another pic which includes both the charging chip and the buck-boost converter \$\endgroup\$ – seanyu24 Feb 8 '18 at 21:42
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    \$\begingroup\$ "always get the wrong output on Pin14 to the battery... many failed to have the correct output.( either 0v or >4,2v)" - So some boards output 0V, and others >4.2V? This is with the battery disconnected, right? What is the purpose of the diode between BATT and HPWR? "TPS63001... always gets heat up" - exactly how hot does it get? Can you measure the current going into it? \$\endgroup\$ – Bruce Abbott Feb 8 '18 at 22:00
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    \$\begingroup\$ What's the load on the buck-boost? How hot is it getting? Did you follow the manufacturer's PCB layout recommendations? What battery are you attempting to charge, do you have a datasheet? \$\endgroup\$ – John D Feb 8 '18 at 22:01

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