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BQ24079: Single LiFePo4 cell charging from usb

Harry Li74
Intellectual 470 points
Part Number: BQ24079
Other Parts Discussed in Thread: BQ25071, BQ25070

I am designing a single LiFePo4 cell charger from usb. 

From the datasheet, BQ24079 have a VBAT target of 4.1V. Just wondering if anyone can tell me if LiFePo4 can handle this voltage? Most LiFePo4 datasheets will say 3.6 as the maximum voltage.

Also, with the dynamic power management (DPM) feature, does it mean that I do not need a separate USB detection circuit?

I have also looked at BQ25071, but it does not mention DPM at all, which is why i hope BQ24079 works out.

Cheers

Harry

  • 0
    TI__Mastermind 21590 points

    Hello Harry,

    The max charge voltage of  LiFePo4 is typically 3.6V so BQ24079 can't be used. The DPM feature is used to prevent collapse of the Input voltage due to heavy load. You can read more about the feature here. The feature doesn't detect the USB. What is the charging current level required?

  • 0 in reply to Raheem
    Intellectual 470 points

    I'm looking for a single cell LiFePo4 charger to be charged from a generic USB port from a PC. USB should always be 5V ish, but the current varies alot.

    Before the enumeration of my MCU, some USB ports will only supply 100mA at the start. If the charger draws more than 100mA then the usb port Voltage will crash and the USB port maybe locked up because the system think it got short circuited. (I got this from googling, if this is incorrect, please tell me.)

    After enumeration, the USB will supply 500mA or 900mA depends on type of the USB port. There's also special USB chargers that supply 1.5A or 2A.

    "VINDPM prevents an adapter from crashing by reducing current instead of voltage. This allows for charging to continue, albeit at a slower pace."

    A quote from the DPM documentation you mentioned, which is why I wanted the BQ24079 for the 100mA supply case. And I can just set the absolute maximum charge current to 450mA so I dont have to care about other types of chargers.

    Due to the variable current nature of the USB ports, I really like the VIN-DPM feature that you guys have inplemented.

    Can you recommend a LiFePo4 charger with the VIN-DPM feature for my design?

    Cheers

    Harry

  • 0 in reply to Harry Li74
    TI__Mastermind 21590 points
    Hello,
    Please take a look at the BQ25070.