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bq24295 PMID pin current limit

Sreekanth Anegunda
Intellectual 975 points

Hello,

I have selected BQ24295 for charging the battery. I have few questions.

1. What is the maximum current can be drawn from the PMID pin. The data sheet says IOTG_LSOCP LSFET cycle by cycle current limit 5A. This means that i can draw maximum of 5A from PMID pin.

2. Can we limit the current drawn from the PMID pin?

3. If I am drawing 2.5A from PMID pin and if I connect a external charger of 1A. What will be the behaviour of the IC.

Thanks & Regards,

Sreekanth

  • 0
    TI__Guru**** 165886 points
    Regarding 1, the maximum warrantied current from PMID over V(BAT) = 2.9V to VBATREG is IOTG = 1.3A. As with any boost converter, as its input voltage (V(BAT) increases, its maximum output current increases. The 5A low side FET maximum current limit is not equivalent to PMID output current. You can estimate maximum output current, using the efficiency power balance : eff = Po/Pi = Vo*Io/ (Vbat * Ibat-avg) where you can estimate efficiency from the d/s figure 4 and Ibat_avg is clamped to IOTG_LSOCP_LSFET. Attempting to pull more current from PMID may result in the voltage at PMID falling below the regulation voltage set in the registers.

    Regarding 2, there is no register to reduce IOTG_LSOCP_LSFET.

    Regarding 3, at lower battery voltages, the voltage at PMID will droop below the regulated value because IOTG_LSOC_LSFET is clamping the boost converter's input current from the battery, effectively turning it into a current source instead of a regulated voltage source.
  • 0 in reply to Jeff F
    Intellectual 975 points
    Hello Jeff,

    Thanks for the response,

    Regarding 1, Understood.
    Is it possible to draw a max of 2.5A of current from the PMID pin? I want to use the IC for charging a Li-Ion battery of 3.7V 25Ah. So if the battery voltage drops to 3V, will I be able to draw 2.5A current?

    Regarding 2, Understood.

    Regarding 3, I have observed that if 800mA current is drawn from the PMID and a external charger of 700mA is connected then the current drawn at the output is reduced to ~550mA.

    I have observed that when the charger IC is connected to PC the output current will become zero and if I connect the charger IC to the external supply the IC I am still able to draw the current at the output.

    BR,
    Sreekanth
  • 0 in reply to Sreekanth Anegunda
    TI__Guru**** 165886 points
    The boost converter will operate in cycle by cycle current limit and attempt to provide the current you request but the output voltage may drop out of regulation.