The new 3.3v and 5v Regulators i need a clarity here

[mnciks11]

Hello guys

i was working on the new lenovo laptop with the new power supply for 3.3v and 5v, below on the picture i circled a resistor that was installed on the Vin power rail for the 3.3v always chip, but i dont understand the fuction and use of the resistor, why it was installed...Please anyone whose more advanced can assist please

[RethoricalCheese]

Re: The new 3.3v and 5v Regulators i need a clarity here

That resistor is a pull-down resistor for the enable pin. But it is strange indeed because EN is connected to Vin. So I guess they had a design change but did not remove the resistor.

[mnciks11]

Re: The new 3.3v and 5v Regulators i need a clarity here

That resistor is a pull-down resistor for the enable pin. But it is strange indeed because EN is connected to Vin. So I guess they had a design change but did not remove the resistor.

Ey I was so confused my brother

[ktmmotocross]

Re: The new 3.3v and 5v Regulators i need a clarity here

that pull dow resistor is for put voltage down fast from capacitors to fast swith down. if it was not there the capacitor can hold charge and EN signal will be active for long time.
every en signal must have capacitor and resistor paralel to ground like EN1 signal

[SMDFlea]

Re: The new 3.3v and 5v Regulators i need a clarity here

The resistor isn`t installed on some other compal boards,it could be a mistake in the schematic ,they didn`t mark it as @ no-stuff.

[mcplslg123]

Re: The new 3.3v and 5v Regulators i need a clarity here

I agree with @smdflea

[RethoricalCheese]

Re: The new 3.3v and 5v Regulators i need a clarity here

Yup, I would say PR339 should not be @ and PR335 should be.

[mcplslg123]

Re: The new 3.3v and 5v Regulators i need a clarity here

Yup, I would say PR339 should not be @ and PR335 should be.

Exactly. You find out the mistake in diagram.

[reformatt]

Re: The new 3.3v and 5v Regulators i need a clarity here

Refer to the datasheet, enable pin is not meant to be left floating. So the 1M resistor ties that logic line to ground when no voltage is present. Prevents erratic operation when power is first supplied.