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BQ25570: Does the Vout pin have to be decoupled?

Part Number: BQ25570

Hello.

Just a quick question. I'm doing a board with BQ25570 in mind, and I'm confused about something. What is the real purpose of the Vout pin (pin #14)? The BQ25570 datasheet (page 4) lists the pin as output, and its description is "Buck converter output. Connect at least 22 μF output capacitor between this pin and pin 15 (VSS)". This makes it sound like the pin has to be decoupled with a 22+ uF cap very close to the pin. But the "7.2 Functional Block Diagram" on page 14 says otherwise and shows the pin as an input instead. By the looks of it, it's actually a sense pin? A part of the output voltage feedback loop?

Anyway, I understand there has to be some output capacitance present in a buck converter, but how close do the caps really have to be to the Vout pin in this case? I've taken a look at the BQ25570EVM-206 eval board, and it doesn't seem to have any caps near it. Moreover, the trace seems to go to the PCB bottom plane by two vias and then back again (introducing some stray inductance).

So, is it safe to assume this pin doesn't need any decoupling i.e. a 0.1uF 0603 (or a 22uF 1210) MLCC right next to it?

Best regards!


  • Hi Thomas,

    The VOUT pin is the voltage sense pin for the buck converter so should not be called an output.  The EVM doesn't have a decoupling cap and no customers have every complained that it was needed but couldn't hurt.

    Regards,

    Jeff