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LTC4040 Charging Issue

Hi All,

I am using LTC4040 to charge 18650 battery and to generate 5V output. Boost section is fine but charging of battery is not working.

I have removed NTC and grounded the PIN. And now LED connected to RST and CHRG pin is flickering alternatively.

PROG pin is showing 0V.

added extra info
[edited by: just_in at 12:56 PM (GMT -5) on 18 Nov 2020]
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  • I see some small blips on PFI. Can you zoom to a smaller timescale and trigger on falling edges right before the average value shown here? Also try setting the voltage range to 500mV or something that would show this more clearly.

    I expect periodic dips on this node even if  PFI is not being triggered just due to input impedance when current starts being drawn.

  • HI Zack,

    You were right. The issue is resolved. Thanks for your support.

    As you said when we zoomed into PFI signal we could see the glitch at every 490ms as shown below.

    Further investigation we understood the same glitch on VIN_FILTRD as well. We supplied external 1.3V to PFI pin (after removing voltage divider in circuit) and then battery started charging.

    So we realized, when battery started to charge at higher current, power supply voltage drops (thus PFI voltage drops below 1.3V). This was momentarily (in uS) because once the PFI voltage drops below 1.2V battery stops charging means no current consumption, and hence input voltage and PFI voltage recover back to 5V and 1.3V respectively. This keeps on happening at every 490mS.

    Now we used separate power cable to connect the input supply and avoided the voltage drop.

  • Great news! Yes, lowering the impedance (wiring) between your input source and the circuit's input is the best solution here if possible. If necessary, you could also lower the PFI threshold.