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BQ24040: BQ24040 Pulsing Current

Josel Go
Expert 6395 points
Part Number: BQ24040


Hi Experts,

Good day.

Our customer likes to ask for some technical advice. They implemented the BQ24040 with the TS function. The TS sets the Vreg = 4.06V at 74degC.

During our testing, they found out the current goes up and down, like a pulse as shown below.

They have some questions below,

1. Is the current pulsing behavior normal in a given condition eg when it reaches the temperature limit?

2. Will the current pulsing damage the IC or battery cell?

 Please advise.

Regards,

Josel

  • 0
    TI__Prodigy 490 points

    Hi Josel,

    Are you testing on the evaluation module (EVM) or another board?  If it's on the EVM, have there been any modifications made on it? If it is not the EVM, can you please provide a schematic?

    What is the test setup and conditions in which this occurs? What is the input voltage, charge current, how is the battery pack connected to the charger IC, etc.?  And what is the TS voltage at which these plots were generated?

    Also, based on the current behavior in the provided plots, the pulsing should not damage the charger IC

    Best,

    Mira

  • 0 in reply to Mira Manivannan
    TI__Mastermind 23775 points

    Hello Mira,

    The customer just got back to us with the ff details below:

    The circuit is mounted on a pcba and inserted in a chamber of 60degC. The charging was started after chamber reaches 60degC for at least 30 minutes.
    The input of the charger IC is connected to USB voltage 5V, 1A. It has a battery cell (positive connects to the output of charger IC, negative connects to GND).
    Unfortunately we only have a TS voltage plot of a similar pcba, we don't have the exact pcba on hand at the moment.

    Understood that the pulsing should not damage the charger IC. Will the pulsing damage the battery cell?

    Apologies, we don't have the TS voltage, but we captured the RT resistance.

    VBAT & RT.zip

    Thanks in advance

    Renan

  • 0 in reply to Renan Santos Adriano
    TI__Prodigy 490 points

    Hi Renan,

    What is causing the Rt to change if the temperature is at a constant temperature?

    And what is the Rt beta and the Rt (aka NTC) resistance value?

    What is reason for including the 3k57 resistor on the TS pin?

    Is there anything in between the OUT pin and the battery cell?

    And are there capacitors attached to the IN and OUT pins of the charger?

    Best,

    Mira

  • 0 in reply to Mira Manivannan
    TI__Mastermind 23775 points

    Hello Mira,

    Please see update from customer below:

    (1) What is causing the Rt to change if the temperature is at a constant temperature?
    I'm not sure unfortunately, I was hoping TI is able to help enlighten me. As the NTC is an SMD, maybe the charging affected it?

    (2) And what is the Rt beta and the Rt (aka NTC) resistance value?
    The beta must be the B-value here, it's 3380.
    Resistance is 10kOhm @ 25degC.

    (3) What is reason for including the 3k57 resistor on the TS pin?
    The 3k57 resistor is to "widen" the range of the temperature cutoff.
    The charging is expected to cutoff at <6degC or >170degC (the 170degC is the max here as this is the max value of the NTC).

    (4) Is there anything in between the OUT pin and the battery cell?
    The OUT pin is connected to a battery cell through a mosfet controlled by MCU, which is always ON throughout the charging process.

    (5) And are there capacitors attached to the IN and OUT pins of the charger?
    Yes, the IN and OUT pins are connected to 1uF capacitors.

    Thanks in advance.

    Regards,

    Renan

  • 0 in reply to Renan Santos Adriano
    TI__Prodigy 490 points

    Hi Renan,

    I'll get back to you tomorrow about this

    Best,
    Mira

  • 0 in reply to Mira Manivannan
    TI__Mastermind 23775 points

    Hello Mira,

    Any update on this?

    Regards,

    Renan

  • 0 in reply to Renan Santos Adriano
    TI__Prodigy 490 points

    Hi Renan,

    Sorry about the delay.

    Could you please provide the TS voltage graph of the similar pcba? Using the aforementioned pcba, could also please recreate the battery current and voltage graphs and the Vout/Rt graphs?


    Also, how physically close is the Rt to the battery and to the charger?

    Best,
    Mira