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BQ25883: 2S1P, 1S1P or 1S2P for a circuit that needs 3.3V?

Eduardo Barcellos
Intellectual 420 points
Part Number: BQ25883
Other Parts Discussed in Thread: BQ28Z610

Hello,

I'm designing a circuit that only needs 3.3V. And so, my initial thought was to use the BQ25883 + BQ28Z610 with 2S1P for 2x 18650 Li-ion cells, each one providing 4.2V (8.4V total), and having a switching regulator on the circuit to regulate it to 3.3V. However, would it be a good option to use 1S1P or 1S2P, and a LDO regulator to regulate it to 3.3V? My concern is not being able to use the entire battery charge that way.

Thanks,
Eduardo

  • 0
    TI__Genius 10385 points

    Eduardo,

    In terms of W-hr, 2s1p and 1s2p would be equivalent. However the advantage of the 2s configuration would be that less current (and therefore less conduction losses) will be needed to power your system load.

    However, a 1S topology would be a better fit if you are looking have  an LDO post-regulate to 3.3V. Could you tell me a little bit more about your application and what features you are looking for from your charger?

    Best Regards,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 420 points

    Ricardo,

    Thanks for your reply. My circuit has one 800x480 touchscreen LCD display, one FPGA, one 8-bit RISC MCU, 2 SRAMs and a touchscreen controller. Its a portable device that the user connects to industrial equipment to configure them using a GUI. And so, it must have a rechargeable battery, and the LCD display must show the battery's state of charge on the top-right corner, like a smartphone does.

    The system drains ~500mA when running, and all of its electronics uses 3.3V, including the LCD display. There's a 5V power plug on it to power the system when its connected, and to also charge the battery from it.

    So, my idea is to use the BQ25883 to charge the battery, and the BQ28Z610 to return the state of charge as well as to protect/balance the cells, having both chips on the same PCB, together with the rest of the system.

    What do you think?

    Best regards,

    Eduardo

  • 0 in reply to Eduardo Barcellos
    TI__Genius 10385 points

    Eduardo,

    As I understand, the integrated ADC is a must have feature for you. If this is the case, I suggest the BQ2589X family of devices.

    Please be aware that in all of our NVDC chargers that the SYS output can vary from the minimum system voltage to the battery regulation voltage. Typically the minimum system voltage for a 1S charger is 3.5V and 4.2V is a common battery regulation voltage. So your LDO design should accommodate this input voltage range ~3.5V to 4.2V.

    I think with either the 1S (BQ2589X) or 2S (BQ2588X) topology you could proceed with similar performance. 

    Best Regards,

    Ricardo

  • 0 in reply to Ricardo
    Intellectual 420 points

    Ricardo,

    After considering your responses and the options available I guess I'll be using 2S1P with BQ25883 for charging & BQ28Z610 for fuel gauge/protection/cell balance.

    Thanks for your help!

    Best regards,

    Eduardo