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BQ25622E: Headroom needed to charge at 3A?

Cameron Wutzke
Expert 3552 points
Part Number: BQ25622E

Hey Team,

I just want to confirm 5Vin @3A is able to charger a 4.45V battery.

There is about 100mΩ between battery and VBUS, resulting in 300mV voltage drop. (5V -> 4.7V)

Is there a maximum duty cycle spec I need to consider as well?

Thanks,

Cameron Wutzke

  • 0
    TI__Mastermind 31510 points

    Hi Cameron, 

    We have verified in lab testing with the EVM that BQ25622E can charge up to 4.45V with ICHG = 3A with a 5V @3A input supply. In my testing I am measuring 5V at the VBUS test point and 4.45V at the BAT test point on the EVM. 

    Mind you on a customer board there will likely be additional parasitic resistance from the adapter port to the charger IC VBUS pin, as well as, between BAT pin and the actual battery terminal. When attempting to charge at a high current such as 3A this may limit a customers ability to practically charge up to 4.45V at 3A with a 5V adapter. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    TI__Expert 3552 points

    Thanks Garrett,

    I guess the next question I'll be asked: what if I don't have enough headroom? I assume the CC charging phase is totally fine, since we likely output 4V and current limit; CV phase would just charge slower? I'm assuming current will decrease as we get closer to the 4.45 termination voltage. Overall this doesn't sound like a showstopper to me. Since CV would charge at slower current than 3A anyways

    Hope for your insights so I sound like I know what I'm talking about with customers ;) 

    Thanks,

    Cameron

  • +1 in reply to Cameron Wutzke
    TI__Mastermind 31510 points

    Hi Cameron, 

    If the headroom is not greater than Vsleepz (typ 220mV) at low current then the buck converter will not function. In general the VINDPM and IINDPM thresholds should be able to be set to prevent the headroom from reducing below Vsleep threshold. 

    For example if parasitic resistance on input side causes VBUS to drop when trying to charge at 3A the first response from BQ25622E will be to reduce charge current in an effort to raise up VBUS. I agree reduction in charge current should not be a showstopper, but customer should be aware charge time may be longer.  

    Parasitic resistance on the battery side of the IC will cause the device to switch from CC to CV phase earlier than it should. Again this is not a showstopper issue, but it will again increase overall charge time. 

    If any of the points I made are not clear to you I am happy to have a webex meeting to discuss in more detail later this week. Mind you I will be out of office tomorrow 10/11, but I have some free time on my calendar the rest of the week. 

    Best Regards,

    Garrett