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BQ24770: 1S clamped current

Scott H.
Prodigy 40 points
Part Number: BQ24770
Other Parts Discussed in Thread: BQ24193

Hello,

We have a 1S configuration. We would like to charge at high current when BAT is below BATLOWV threshold, bypassing pre-charge and fast-charge clamps. Can we do this by setting SYSMIN (min sys voltage). If not, is there another register setting for this?

From datasheet section 8.6.6, for reference:

For 1s charging, the charge current is clamped at 384 mA when battery is below BATLOWV threshold. When
battery is between BATLOWV and SYSMIN, the charging current is clamped at 2 A. When battery is above
SYSMIN, the charging current follows register setting.

Thank you.

  • 0
    TI__Genius 11850 points

    Hi Scott,

    Unfortunately, there is no clean way to do this. With a 1s configuration, when VBAT < BATLOWV, the pre-charge current is clamped to 384 mA.

    How high of a pre-charge current do you need, and may I ask why your application requires this?

    Our charger ICs use a lower pre-charge current in order to safely charge a deeply discharged battery. In many applications, the battery pack has a protector circuit which opens when the battery voltage falls below ~3 V anyway, so the battery should only spend a short time in the pre-charge phase before being fast charged.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 10 points

    Hi Angelo,

    Thank you for writing back.

    We have a LiFePO4 cell that may get introduced to the charger at 2.5V (Also our protection ckt. limit). We need 4A to charge the cell in our required time, and also need the flexibility to increase the rate in certain situations.

    Any pre-charge would need to be short lived and as high as possible. The BQ24770 fast charge stage (2A) is too low as well. The trip from 2.5V to BATLOWV then to SYSMIN kills our time budget. 

    Feel free to ask any more questions.

    Thank you,

    Scott

  • 0 in reply to Scott. H.
    TI__Genius 11850 points

    Hi Scott,

    Understood, thank you for explaining this.

    It sounds like a different charger IC may be a better fit for your requirements. Can you please answer the questions below so I can provide further suggestions?

    • Need to charge a 1s LiFePO4 battery
    • At least 4 A charge current
    • Must charge as fast as possible even when the battery voltage is only 2.5 V
    • Charger IC should be host-controlled in order to flexibly change charging parameters on the fly. Do you have a preference between I2C and SMBus communication?
    • What will be the input voltage to the charger IC?
    • Will there be a system load connected to the charger IC output? If so, how much voltage and current will it draw?
    • Any other requirements?

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 40 points

    Hi Angelo,

    • Need to charge a 1s LiFePO4 battery
      YES

    • At least 4 A charge current
      YES; 8A MAX

    • Must charge as fast as possible even when the battery voltage is only 2.5 V
      YES

    • Charger IC should be host-controlled in order to flexibly change charging parameters on the fly. Do you have a preference between I2C and SMBus communication?
      Host-controlled for charge, charger/host "left behind" when load on battery power.
      SMBus preferred, not critical.

    • What will be the input voltage to the charger IC?
      12VDC

    • Will there be a system load connected to the charger IC output? If so, how much voltage and current will it draw?
      YES: Switcher capable of 2V-5V IN; 3.3V out, 40mW max. load.

    Thank you again for your attention on this.

    Scott

  • 0 in reply to Scott H.
    TI__Genius 11850 points

    Hi Scott,

    Thanks for the information. I believe the simplest solution for your application is a charger from the BQ2419x family, such as the BQ24193. The charge profile is shown below.

    Here are some key BQ24193 parameters that are relevant to your application:

    • Maximum input operating voltage = 17 V
    • Max charge current = 4.544 A
    • Max precharge current = 2.048 A
    • VREG can be set as low as 3.5 V to accommodate LiFePO4 batteries.
    • The Default BAT_LOWV threshold is 3 V, but this can be changed to 2.8 V through I2C control. Therefore, the BQ24193 will apply the 2 A precharge current until your battery rises above 2.8 V, at which point the full fast-charge current will be applied.
    • The NVDC topology makes it easy to regulate the VSYS rail for your system load. With a traditional topology charger, VSYS can go as high as your adapter voltage (12 V), so you would need a separate buck converter to step VSYS below 5 V.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 40 points

    Thank you for your help Angelo, we will look into the device family you recommended.

    Scott