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Original question:

BQ24610: Problems about charging

BQ24610: BQ24610: Problems about temperature

user6051029
Prodigy 200 points
Part Number: BQ24610
Other Parts Discussed in Thread: CSD18531Q5A

Hi,

The schematic diagram of the circuit being debugged is as follows.

The relevant parameters are as follows.

(1) Input voltage : 24V;

(2) Battery charge voltage : 12.6V;

(3) Battery charge current : 2.8A;

(4)Precharge and termination current : 0.3A;

(5)Safety timer: 9.3h (CTTC-0.1uF);

Charging function is normal, but the chip bq24610 temperature is very high. The surface temperature of the inductor is also very high. Heat sink pad is connected to GND, and copper coating area is also large.

Please help to analyze the possible reasons.

p.s. Input voltage is 15V, the temperature is not high.

  • 0 in reply to user6051029
    Prodigy 200 points

    Schematic diagram is shown in the attachment.

    Best regards!

  • 0 in reply to user6051029
    TI__Mastermind 25800 points

    Hello,

    I recommend you first measure your charging efficiency at both 24V and 15V input voltage. 

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Prodigy 200 points

    Hi,

    There is no significant difference about charging efficiency. Charging parameters are the same at both 24V and 15V input voltage.

    Battery charge voltage : 12.6V;

    Battery charge current : 2.8A;

    (1) Is it correct to use bq24610 in this way? (Battery charge voltage : 12.6V, Input voltage: 24V)

    (2) Could you theoretically help to analyze the causes of different heating of different input voltage? The difference between input voltage and charging voltage is large, it's turned into heat consumption, right? Is it related to MOSFETs Qg?

    (3) In addition to PCB layout, what about the possibility of high temperature?

    Please help analyze this problem.

    Best regards!

    John

  • 0 in reply to user6051029
    TI__Mastermind 24075 points

    Hi John,

        The difference in input voltage causes power loss and heat dissipation on the high side MOSFET. The MOSFET gate driver power loss is given by Piclosss_driver = Vin*Qg_total*fs. Increasing the input voltage will increase the loss, however selecting a MOSFET with lower Qg (total gate charge) will decrease the loss seen. MOSFET gate-driver power loss contributes to the dominant losses on the controller IC when the buck converter is switching.

    Yes Bq24610 can be used with an input voltage up to 28V. and output charge voltage of 26V. The only consideration is that there is enough headroom so part does not enter SLEEP mode (1 to 2V headroom between VIN and charge regulation voltage) so for your application there should be no issue.

  • 0 in reply to Kedar Manishankar
    Prodigy 200 points

    Hi Kedar,

        I still have two questions, please help to answer.

        (1) I compared the parameters of three MOSFETs, CSD18531Q5A（used in my application）,FDS4887(used in the TI Demo borad),SiS412DN(used in the bq24610 datasheet on Page 26), as shown in the attachment. Qg of SiS412DN is lower. Do you recommend it more? However, are there any obvious problems in using the other two in this occasion? Please help analyze this problem.

        (2) You suggest that the battery is 1 to 2V headroom between VIN and charge regulation voltage. If the adapter can only select 24V, and the charging voltage is 12.6V. Do you have any good measures to avoid overheating of bq24610 and MOSFET during charging?

        Thank you very much!

        John

    Qg Contrast.docx

  • 0 in reply to user6051029
    TI__Mastermind 24075 points

    Hi John,

       Selection of MOSFET depends on system, and you should take into account both conduction and switching losses. Section 10.2.2.4 Power MOSFETs Selection of the datasheets does a good job of explaining the different MOSFET parameters to take into account when selecting your external MOSFET.

     I suggested that you need atleast  1V to 2V headroom between VIN and charge regulation voltage, to avoid entering SLEEP threshold. There is no issue with 24V input and 12.6V charge regulation voltage.

    Section 12 Layout gives key pointers when designing layout, as layout has the biggest role regarding overheating. Choosing a lower Qg MOSFET will also help reduce heat.