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Schematic Check for LTC4007

Category: Hardware
Product Number: LTC4007

LTC4007 datasheet provides typical application circuit for a 3-cell, 4A LiPo battery charger. I have read the datasheet and designed the following circuit. We have fabricated the board, and are now testing it. However, the circuit does not charge the battery. The circuit turns on FET Q4, but holds Q3 and Q5 OFF, therefore nothing is switching. Why is the circuit remaining off? The input voltage is 11.8V and the battery voltage is 11V. With those voltages, the chip should detect the lower battery voltage and start charging. I do not see any reason why the chip would be in a disabled state. The NTC detect should be disabled due to the 309kohm resistor. I disabled the input supply current limited via connecting CLP and CLN (as recommended in datasheet). I set the programming resistor and sense resistors per datasheet as well.

If anyone knows why this circuit isn't charging the battery, please let me know!! Thank you!

Thread Notes

  • Could the problem be that the NTC fault is tripping? I put 309kohm from NTC to DCIN, as specified in the datasheet to disable the function. However, the datasheet shows a sample and hold capacitor there, so I'm confused if we require that capacitor/resistor pair for the NTC to be disabled properly.

    I measure 8.6V from NTC to GND, with a 12V input, which gives 11uA current through the NTC. The datasheet says 10uA minimum and 30uA max to disable the NTC.

  • Also note, I do not have pull up resistors on ACP, FAULT, or FLAG. It seemed like those were optional so I left them floating. Can that cause a problem?

    I just soldered a 100kohm pullup on ACP but the circuit still does not charge, so hopefully that pin isn't a problem to be left floating

  • SOLVED: The issue is because the SHUTDOWN pin was left floating. Once pulled to GND, the circuit begins to charge the battery. For now, the circuit only charges at 1A (instead of the desired 4A) but I will probably figure out the issue there soon.

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