PCA9420 Power Up and Operation

[Kevin23]

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?

[GeoZh]

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.

[Kevin23]

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?

[guoweisun]

• 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.

[Kevin23]

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?

[guoweisun]

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

what's the voltage range of your battery?