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BQ24170: Efficiency vs charge current

na na78
Guru 16770 points
Part Number: BQ24170

Hi

Could you please explain Efficiency vs Charge current?

For example, charge current is 0.5A and efficiency 87% at VIN=15V 2 cell, according to Figure 12.

What is this efficiency stand for?

Regarding to Figure 12, if 15W output power is required for the system while charging the battery by 500mA, how to calculate input current capability?

BestRegards

  • 0
    TI__Expert 8690 points
    Hi,

    In Figure 12, input voltage = 15V, battery voltage = 3.8V*(amount of cells in series). So for the purple curve, you get VIN = 15V, VBAT = 7.6V.

    Output power depends on where you connect the system, either at the battery or at PVCC.

    If system is connected to the battery:
    1. Max output power = 15W + 8.4V*0.5A = 19.2W
    2. Max output current @ max output power ~ 2.3A
    3. Efficiency at maximum power ~ 92%
    4. Max Input current = 19.2W/(15VIN*0.92) = 1.4A
    5. Input current capability must be at least 1.5A

    If system is connected to PVCC:
    1. Max Power through buck converter = 8.4V*0.5A = 4.2W
    2. Max Input Current = 15Wsys/15VOUT + 4.2W/(15VIN*0.87) ~ 1.35A
    3. Input current capability must be at least 1.5A

    For both cases, you would still need 1.5A input current capability to make sure the adapter does not crash.

    Regards,
    Steven