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TPSM828301: maximum output capacitance

Mark Goodberlet
Prodigy 90 points

Part Number: TPSM828301
Other Parts Discussed in Thread: TPSM828302,

Page 12 of April2025 datasheet says:

"Larger output voltage combined with large output capacitance can trigger an over current event and prevent the device from starting up correctly. The circuit designer needs to select the maximum output capacitance in accordance to the target output voltage and start-up time."

Your WEBENCH design for my application suggests 22uF output capacitance - but my SoC/ASIC circuits could add another 150uF. 

1) How to determine maximum output capacitance that allows device to start up correctly?

2) Will using TPSM828302 instead of TPSM828301 help prevent startup problems due to high output capacitance?

  • +1
    TI__Mastermind 29370 points

    Hello Mark,

    thanks for reaching out in E2E.

    1) The soft-start time is specified with typ. 300μs. The current limit of the TPSM828301 is specified with 2.1A (typ.). The maximum output capacitance can be calculated depending on the output voltage according to the simplified formula I = C · ΔV / Δt → C = I · Δt / ΔV → COUT(max) = 2.1A * 300μs / VOUT. At a maximum allowable VOUT of 4.5V this would result in COUT(max) = 140μF. COUT(max) can be higher for lower VOUT. The maximum recommended output capacitance is specified with 200μF in section 6.3 of the datasheet, which is considering loop stability.

    2) Yes, a higher current limit would allow a higher output capacitance at the same soft-start time. But as mentioned before the maximum recommended output capacitance from loop stability perspective is 200μF.

    Best regards,

    Andreas.

  • 0 in reply to Andreas Mueller
    Prodigy 90 points

    Hello Andreas,

    Thanks for a very detailed and thoughtful response!!

    -have a great day,

    Mark