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BQ24610: choke hot

GARETH OU
Guru 11365 points
Part Number: BQ24610

Hi 

When a customer used BQ24610, he found that there was a jitter at the phase node, causing the inductor to heat up. How to solve it?

The low gate is only opened a little, and the purple output looks fine.

  • 0
    TI__Mastermind 29882 points

    Hi Gareth, 

    Thank you for reaching out!

    The schematic image posted is not very clear. Could you please provide a pdf version? 

    Also, what are the charging conditions of your design?

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Guru 11365 points

    Hi Aya

    Please refer to the attached schematic

    bq24610 schematic.pdf

  • 0 in reply to GARETH OU
    TI__Mastermind 29882 points

    Hi Gareth, 

    Thank you for providing. I will review and get back to you with feedback by Friday. 

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    TI__Mastermind 29882 points

    Hi Gareth, 

    Overall, the schematic looks good. I do have one comment about the output capacitance below (~ 66.1uF)

    Please see the table below with recommended output capacitance values as a function of charge current. Moreover, the recommended resonant frequency range is between 12-17 kHz. With your current value of 66 uF, the LC output filter resonant frequency is 7.51kHz. 

    I recommend decreasing the capacitance to ~20uF to see if that resolves the jitter at the phase node. 

    Please let me know if you have additional questions/concerns. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Guru 11365 points

    Hi Aya

    1. The customer also found that there is a problem of burning the upper and lower bridge MOS (FKBB3002). They have measured the waveform as shown in the attachment (Math=HIDRV-PH). Is there a risk to fix it though?

    2. If the HIDRV and LODRV frequencies cannot be locked and the constant jitter causes the choke to be very hot, will it cause damage to the MOS?

    Will the small dead time of HG and LG cause a shoot though?

    How to adjust the dead time?

    Adding the vin current (green) waveform, it seems that there is no shoot though
  • 0 in reply to GARETH OU
    TI__Mastermind 29882 points

    Hi Gareth, 

    GARETH OU said:
    The customer also found that there is a problem of burning the upper and lower bridge MOS (FKBB3002).

    1- Could you please clarify the conditions under which the MOSFETs are burning? 

    2- Are there any changes made to the schematic posted previously (is the output capacitance decreased?)

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Guru 11365 points

    Hi Aya

    After adjusting C24, C29 and C30 to 0.22uF, the jitter has improved. The measured Rsense voltage is 26mV, but the LDRV waveform as shown below appears The schematic also removes D29 (Zener diode) Customer feedback that removing the output capacitor only has 22u is ineffective.

  • 0 in reply to GARETH OU
    TI__Mastermind 29882 points

    Hi Gareth, 

    I am glad to hear that the jitter has improved. The improvement is most likely due to the removal of D29. 

    You could try readjusting C24, C29, and C30 to 0.1uF and observing the behavior.

    Please let me know if you have additional questions/concerns. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Guru 11365 points

    Hi Aya

    Why is the measured Rsense voltage 26mV, but the LDRV waveform is very small, and it feels like it is asynchronous?
    Test status
    Vin 19v, cell x3 is set to 12.3v,
    The current battery voltage is only 11.2v
  • 0 in reply to GARETH OU
    TI__Mastermind 29882 points

    Hi Gareth, 

    I will look into this and get back to you by the end of the week. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    TI__Mastermind 29882 points

    Hi Gareth, 

    Apologies for the delay here. 

    The charger operates in nonsynchronous mode when the SRP-SRN voltage is below 5 mV (0.5-A inductor current for a 10-mΩ sense resistor). Since the measured voltage is 26mV, the charger should not be in nonsynchronous mode.

    Best Regards, 

    Aya Khedr