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TPS65218D0: DCDC4 capacitor

shigehiro tsuda
Mastermind 9490 points
Part Number: TPS65218D0
Other Parts Discussed in Thread: AM4376, TMDXEVM438X-EPOS, TMDSEVM437X

Hi,

The TPS65218D0 DCDC4 has the following specifications.
DCDC4 (3.3-V BUCK-BOOST) / ANALOG AND I/O
COUT Output capacitance value min 40 typ 80 max 100 µF

Is it a problem if the bypass capacitor supplied by DCDC4 uses more than 100uF?

Customer want to use VDDSHV1..11 of AM4376 only at 3.3V, and if it is used with the recommended VDDSHV1..11 = 10.02 or 10.06uF of the following recommended value of AM4376 datasheet, the total exceed 100uF.
In addition, they think that total = about 200uF because other devices need a bypass capacitor.
AM4376 datasheet
5-10. Power-Supply Decoupling Capacitor Characteristics

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Mastermind 30260 points

    Please refer to the TMDSEVM437X or TMDXEVM438X-EPOS EVKs for AM4x processors.

    Both of these designs were built using TPS65218xx PMIC and have significant extra capacitance on DCDC4 output. These designs work without issue.

    The maximum amount of capacitance is typically defined as the locally placed output capacitance, immediately following the inductor. Some additional remote capacitance is always require near the processor and other digital ICs running off the 3.3V rail. This is expected.

    Too much output capacitance, however, could cause the output voltage to rise too slowly and eventually the PMIC would fail to turn on the DCDC4 rail within the allowed turn-on time (5ms). If the 5ms timer expires or the current limit is exceeded, the PMIC will reset. Because this fault is happening during the initial power-on, the PMIC would get stuck in a loop.

    However, if your design is similar to the working EVKs, I do not think this will be an issue.

  • 0 in reply to Brian Berner
    Mastermind 9490 points

    Hi Brian,

    Thank you for quick reply.
    I understand that the maximum amount of capacitance is typically defined as the locally placed output capacitance.

    Is it correct to indicate the following capacitor in Figure 1-1. Simplified Schematic of TPS65218D0 datasheet?

    AM437x EVM uses 10uF as follows.
    Should the customer board use 47uF?
    Spec of DCDC4 output capacitance value is "min 40 typ 80 max 100 uF"

    Best Regards,
    Shigehiro Tsuda

  • 0 in reply to shigehiro tsuda
    TI__Mastermind 30260 points

    Yes, 47uF+100nF is the recommended locally-placed output capacitance for DCDC4, placed as close as possible to DCDC4 pin on the IC (pin 15).

  • 0 in reply to Brian Berner
    Mastermind 9490 points

    Hi Brian,

    Thank you for quick reply.

    I understand with your detailed answer about the processing of DCDC4 capacitor.

    Best Regards,
    Shigehiro Tsuda