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TPS7A47-Q1: Regarding post dc-dc converter regulation

Unnimaya V
Prodigy 240 points
Part Number: TPS7A47-Q1
Other Parts Discussed in Thread: UCC25800-Q1, TPS7A47

Tool/software:

Hi Expert

We are utilizing TPS7A47-Q1 as a post regulator for the UCC25800-Q1 in the Gate driver bias supply application for 4kW DC-DC converter.

I would like to know that During the soft start time how much peak current can support by this LDO ?

Additionally, for the application mentioned above, does the feed-forward capacitor (CFF) at the sensing pin offer any advantages, or does it cause any disadvantages?

Thanks and Regards
Unnimaya.V

  • 0
    TI__Genius 10030 points

    Hi Unnimaya,

            During soft start, the TPS7A47-Q1 can source up to its internal current limit (1.0A min, 1.26A typ).

            If you're using the device in an adjustable configuration with an external divider, a feedforward capacitor will help improve transient response, PSRR, and noise, but may impact startup time depending on the capacitance chosen. 10nF is fairly typical. More information on optimizing transient response can be found in this white paper: https://www.ti.com/lit/an/slva289b/slva289b.pdf

    Best Regards,

    Alex Davis

  • 0 in reply to Alex Davis
    Prodigy 240 points

    Hi Alex 

    We are using (4 X 10uF) Ceramic capacitor with 1m Ohm ESR is using at the output side this will help to improve the transient response and Noise? or still need CFF in our application?

    We are also using the UCC25800-Q1, which is an LLC IC. Therefore, the LLC should prevent PSSR noise from passing through, correct?

  • 0 in reply to Unnimaya V
    TI__Genius 10030 points

    Hi Unnimaya,

    If you are using the any-out functionality of the TPS7A47 to configure its output voltage, then the output capacitance itself should be sufficient. If you are using an external voltage divider to configure the output voltage instead, I'd suggest at least providing a provision in your layout for an external feedforward capacitor. That way, should the output capacitance alone provide the required transient response, the capacitor can simply be omitted from your final build. 

    The LLC converter's PSRR will help isolate the LDO from noise or transients on your incoming power supply, but the LLC will add additional noise and ripple that will need to be attenuated by the LDO's PSRR. 

    Best Regards,

    Alex Davis