@Newbie VDD is an internal voltage rail inside the charger IC. It can be supplied from different places. When the power supply (USB) is connected to the IN pin, then VDD it's supplied from the IN pin. When the external supply is absent and the device is powered from the battery, then VDD is powered from the battery (V_BAT).

[That's my reading of the datasheet. Maybe I should make an answer out of it.]

Notwithstanding the line in the Absolute maximum ratings which mentions VDD.

@NickAlexeev, Thank you for the comment. When you say,"When the external supply is absent and the device is powered from the battery, then VDD is powered from the battery (V_BAT)." - You mean to say, the battery is connected to Vbat and GND, as well as IN pin and GND, is it? That's not possible or doesn't make sense, right?

@Newbie What's confusing you?

@Newbie What's the purpose of the IN pin, in your understanding?

The vdd terminology is not very clear. I

You may have to live with that.

Or make sens of the terminology. I'm helping you with that.

@NickAlexeev, the IN pin is the input pin. It is there to provide power to the OUT pins as well as the Vbat pins. When you say, "When external supply is absent" - I understand that IN pin is not connected to anything. Next you say, "the device is powered from the battery" - "So, the Battery is connected to IN pin & GND" ?

Or complain to Microchip and wait until they issue another version of the datasheet.

Or pick another charger with a clearer terminology.

@Newbie The battery is always connected to the Vbat pin (and never to the IN pin). When the charger charges the battery from the external supply, current flows out of the Vbat pin. When the device runs on the battery (without the external supply), the current flows from the battery back into the Vbat pin.

@NickAlexeev, thank you for the clarification. So you mean to say, - "When the device runs on the battery, the current from the battery back into the Vbat pin and then into the Vdd rail? or does it go back into the Vbat pin and then go to the OUT pins?"

@Newbie Pretty much. When the device is running on the battery, the current from the Vbat pin supplies the VDD rail inside charger. Most of the battery current, of course, goes to the OUT pin and powers the rest of the device.

@Newbie Check out section 4.1 in the datasheet. It describes undervoltage lockout (UVLO).

@NickAlexeev, so that condition basically is based on the UVLO condition?

@Newbie Yes... I don't see anything else in the datasheet.

@Newbie The CE pin can put the charger into shutdown too.

Thank you @NickAlexeev. In my testing, when the "No battery present" condition, both STAT pins should be in High-Z. But in that case, I am getting both are Low only. Any idea on why that happens too?

@Newbie How do you observe the STAT pins? Do you have LEDs connected to them?

Yes @NickAlexeev, I have LEDs connected to both STAT pins.

@Newbie I don't have a solid hypothesis. Just thinking out loud. Accourding to table 5-1, both STAT pins are low in case of Temperature Fault or Timer Fault .

Yes @NickAlexeev, I too noticed that in the flowchart.

Maybe, if you have sometime to help, I have another question on the Timer feature of the charger IC over here below. If possible, could you please help me with some clarification on it as well. Would be grateful. Thanks! :)

@Newbie It's late here. I'll look tomorrow.

tweaktown.com/news/90807/…

Happened in November and they've finally decided to tell us about it...