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BQ24100: output inrush current

Paul Antunes
Intellectual 2550 points
Part Number: BQ24100

Dear BMC team,

One customer reported below issues when experimenting bq24100EVM.

For his application, customer may connect battery to the ouput of bq24100 while no voltage is applied at input.

In such case, he measured high peak current taken from battery (up to 18A).

Can customer damage our device when power is applied at output with no power supply at input?

What is your recommendations to limit the peak current ?

Second concern from customer is about Vbat voltage when no battery is connected. He measured 4.3V (Vbat is blu plot). Is it normal behavior ?

thanks

Paul

  • 0
    TI__Genius 12090 points

    Hi Paul,

    Could you please send the waveform again? I can't see the waveform.

    Q1:

    You mean customer connected battery to OUT pin or after the inductor? Where is the system connect to? Could you provide the schematic for us to check if there is anything wrong?

    Q2:

    Battery detection would pull up BAT periodically. I tested with our EVM  and the high voltage is at 4.36V, waveform is shown below.

    Best regards,

    Ann Lien

  • 0 in reply to Ann_Lien
    TI__Intellectual 2550 points

    see attached document with customer waveforms

    Q1: Customer performed tests using bq24100-evm and so schematic is same as evm. Customer has not applied any HW changes. He connected battery to connector J2 with no source voltage on J1. He observed high peak current flowing from battery into the EVM. I do assume it is due to output capacitor but I want to be sure no current flowing back to our device internally and so damage our circuit.

    Q2: customer got same results and he is wondering why the voltage ramp up to 4.36V while bat charge termination is 4.2V. He would know if it is normal behavior of the part.

    Q3: customer has observed ripple voltage at input (connector J1) and high peak current during adapter hot plug-in. Do you have any solution for customer to limit as much as possible inrush current? Again he used EVM for testing.

    customer waveforms.docx

  • 0 in reply to Paul Antunes
    TI__Genius 12090 points

    Hi Paul,

    Q1:

    I tested with battery simulator and real battery, there is no high in-rush current occurred(<3A). According to EVM schematic, there is only one 10uF capacitor at BAT(C9 is open). It won't be that high in-rush current. The inrush current is caused by output capacitor and would only pass through the capacitor. But you need to minimize the trace between battery connector and output capacitor to prevent introducing high voltage to our device(parasitic inductance on trace).

    Q2:

    It will inject one constant current(Iwake) to see if VBAT would increase. it will regulate voltage at one level higher than VOREG. You can refer to datasheet section 8.3.16 battery detection and the block diagram.

    Q3:

    I still can't see a high in-rush current in our EVM board since when adapter plug-in, charger will delay and start to charge. The only thing would cause in-rush current is the input capacitor. If the inrush current would influence your system, you can control one FET by external circuit to implement soft start or just implement the reducing in-rush current connector.

    Best regards,

    Ann Lien