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Original question:

BQ25723: BQ25723: input MLCC

BQ25723: 4uF definition

Brian Chan
Expert 6460 points
Part Number: BQ25723

Tool/software:

Hi Team

extended question from previous E2E post.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1531058/bq25723-bq25723-input-mlcc?tisearch=e2e-sitesearch&keymatch=bq25723#

From the BQ25723’s application information, could you help to share how do you define the minimum 4μF effective? This suggested capacitance is based on what kind of test condition? Thanks.

 

At the VBUS input with a 2.2-μH or smaller inductor, a minimum 4 μF effective (4 × 10-μF MLCC) is suggested for a 45-W to 65-W adapter

BRs

Brian

  • 0
    TI__Mastermind 33035 points

    Hi, Brian,

    The minimum 4uF is assured by design, and verified on bench to be stable for 45W to 65W power level. Note 4uF is effective capacitance, after DC bias derating curve. Since this is input capacitance, which is suitable for 1S to 4S battery configurations. Please refer to the BQ2572XEVM for implementation guide. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    TI__Expert 6460 points

    Hi Tiger

    appreciate your great support

    may I know which part of EVM guide line as below I should refer?

    https://www.ti.com/lit/ug/sluuc74/sluuc74.pdf

    BRs

    Brian

  • 0 in reply to Brian Chan
    TI__Expert 6460 points

    Hi Tiger

    Can you share the detailed test conditions and waveform captures

    BRs

    Brian

  • 0 in reply to Brian Chan
    TI__Mastermind 33035 points

    Hi, Brian,

    The minimum capacitance applies for all test conditions. If the customer found some corner cases, we will be glad to look into for them. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    TI__Expert 6460 points

    Hi Tiger

    because customer side meet Vin drop when CPU load transient in specific USB PD adapter.

    they have some question as below.

    1. When BU test load transient to determine effective input caps value. how BU side test it? only on EVB and apply one kind of USB PD adapter?

    2. when BU side test the load transient as above. may I know what is your Vin drop spec? what % is in our charger spec.

    BRs

    Brian

  • 0 in reply to Brian Chan
    TI__Mastermind 33035 points

    Hi, Brian,

    Brian Chan said:

    1. When BU test load transient to determine effective input caps value. how BU side test it? only on EVB and apply one kind of USB PD adapter?

    We optimize the system cap for load transient. The input is with a bulky input cap 33uF as shown in BQ25723EVM. We use bench power supply instead of PD adapter. 

    Brian Chan said:

    2. when BU side test the load transient as above. may I know what is your Vin drop spec? what % is in our charger spec.

    The input drop is a system spec, varying from customer to customer.  I would suggest starting with 5%. 

    Regards,

    Tiger

  • 0 in reply to Tiger Zhou
    TI__Expert 6460 points

    Hi Tiger

    could you help me check below waveform from customer side is ok for you? I think the Vin drop more than 5%.

    Attaching VIN drop waveform for reference. EXT_DC_IN_C6321 is VIN of BQ25723

    When they add 25V 100uF electrolytic capacitor we can see the waveform is improve.

    and we find only some type-c adapter will happen as below PN

    customer side key concern is they need to know when BU side calculate the effective capacitor. do you also think the corner as above adapter which capacitor may be very low?

    BRs

    Brian

  • 0 in reply to Brian Chan
    TI__Mastermind 33035 points

    Hi, Brian,

    It looks the customer can add more input capacitance. 

    Regards,

    Tiger