topic PCA9420 Power Up and Operation in Power Management

PCA9420 Power Up and Operation

Kevin23 — Thu, 20 May 2021 12:35:26 GMT

I am using the PCA9420 PMIC with the RT685. I need to be able to power up with only VBAT connected (no external voltage on VIN). It appears a voltage on VIN is required for power up. I am not using VIN directly because our input voltage was falling too close or hitting to the 3.1V UVLO on VIN and not powering up. Is it acceptable to use the VBAT voltage with a diode connected to VIN for power up?

I will be inputting 3.3V on VBAT. This will result with VIN being 3.0-3.1V with the diode drop. In testing this appears to work as all regulator enable to the proper voltage and the SYSRST is released. I know the VIN is close to the UVLO but does not seem to disable the regulator outputs if it falls below the default 3.1V VIN_UVLO. The ASYS voltage should be valid and use the VBAT input as it is higher than VIN. I plan on leaving the PMIC powered in the configuration (VIN powered by VBAT with diode).

Is this a valid power up and operational design?

Re: PCA9420 Power Up and Operation

guoweisun — Fri, 21 May 2021 06:44:00 GMT

which kind type of battery do you use in your case?

what's the voltage range of your battery?

Re: PCA9420 Power Up and Operation

Kevin23 — Fri, 21 May 2021 12:27:54 GMT

Our VBAT input will be 3.0-3.6V.

We had some confusion on the power up in section 8.10.3 of the datasheet. In condition 1, we though a valid voltage on VIN was required for power up. We think inputting a voltage on VBAT, with VIN floating, will satisfy "A voltage on ASYS higher than ASYS_UVLO, a 2.8V typical" and should start the power up sequence. Is this correct?

Re: PCA9420 Power Up and Operation

guoweisun — Mon, 24 May 2021 05:25:48 GMT

• A valid VIN supply on VIN pin
• A voltage on ASYS higher than ASYS_UVLO, a 2.8V typical

Please meet above these two conditions.

Re: PCA9420 Power Up and Operation

Kevin23 — Mon, 24 May 2021 23:09:48 GMT

Both conditions must be met? VIN must be supplied? This seems odd for battery powered devices.

In testing we are able to power up with just VBAT and no voltage on VIN. ASYS will be powered by VBAT.

What is the valid voltage on VIN need for if a battery (VBAT) is attached?

Re: PCA9420 Power Up and Operation

GeoZh — Tue, 04 Jun 2024 04:47:20 GMT

Hi,Kevin!

I‘ve tested powering only the VBAT pin without powering the VIN. A battery(400mAh, 3.7-4.2V) was connected to VBAT.The PCA9420 worked properly in my case.This may be helpful to you.