LTC4040 Charging Issue

Hello,

Have you tried this on multiple boards to rule out an assembly issue?

Make sure your input voltage is not drooping at the chip input. This can happen if you are operating near the PFI threshold or if you have long leads between your power supply and the chip input.

If that does not resolve the issue, can you send your schematic?

Regards,

Zack

Hi Zack,

We have tried 3 different assembly and issue remains the same. I have attached the schematics.

Voltage measured on net VIN_FILTRD is 5V.

We have observed 4.16V at battery terminal when battery is not inserted, and as soon as the battery inserted voltage will be same as battery voltage.

Also another observation is voltage on net VPROT is flickering at around 500mS.

We have also observed IGATE & PROG PIN waveform. This indicates aprox 490mS Gate voltage is flickering.

Which plot is which? And can you watch VIN on the scope and watch for quick dips below the PFI threshold?

Regards,

Zack

First plot is IGATE - Amplitude is 8.12V,Period 490mS,Width 2.84mS (Bottom image on first plot is single pulse of IGATE pin zoomed in)

Second plot is PROG - Amplitude is 8.71mV,Period 490mS,Width 1mS (Bottom image on second plot is single pulse of PROG pin zoomed in)

PFI is consistently 1.32V as seen in below image

.

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.

Regards,
Zack