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PF3000 Coin Cell Charger Control in OFF state

Question asked by Bill Gessaman on May 23, 2018
Latest reply on May 25, 2018 by Bill Gessaman

I'm using the PF3000 in an i.MX7D system that has a LiIon main battery that is replaceable by the end user.  When the end user powers off the product, the PF3000 is in the OFF state and the PF3000 data sheet clearly states this:

   "In the OFF state, coin cell charging is not available as the main battery could be depleted unnecessarily."

 

I appreciate the attempt by the PF3000 designers to help avoid a system issue that might drain the main battery where the capacity is unknown, but this design choice represents an inflexible side effect that I believe is undesirable.  Without at least some minimal charging current in the OFF state, the connected supercap or LiIon button cell is subject to self-discharge and leakage of the LICELL pin on the PF3000.  In our case, the supercap in our system discharges over a period of about 5 days to about 1.8 volts.  If the main battery is removed after the product is powered OFF for these 5 days or more, then the end user gets surprised that their Real-Time Clock in the i.MX7D is lost and needs to be set again.

 

Each application differs in the capacity of the main battery used, so to hard wire this behavior into the PMIC can lead to undesirable behavior.  If the PF3000 provided the same reduced charging current of 10uA in the OFF state as it does in the Sleep or Standby states then individual application system software could choose how to manage the COINCHEN bit in the COINCTL register of the PF3000.

 

  1. Are there any options available to avoid this behavior in the PF3000 PMIC?
  2. If not, would it be reasonable to hope that future PMIC implementations would take this issue into consideration?

 

Thanks,

Bill Gessaman

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