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I am using an MP2325 buck converter (datasheet) to drop a 24v supply down to 5v to supply a Raspberry Pi.

The datasheet above details Pin 7 as VCC a "Bias Supply" (page 7) and mentions nothing else about that pin in the datasheet.

I have found this app note from TI: Benefits Using a Buck Converter's External Vcc Bias Pin which says:

Several DC/DC converters on the market have an additional pin that accepts an externally applied voltage.... An external bias voltage, also called a split-bias rail voltage, above the internal LDO's output voltage will override the internal LDO and enhance the efficiency of the converter by eliminating its power loss. The VCC current will be supplied from the external bias instead of the internal LDO.

However all of the example schematics from Monolitic in their datasheet show VCC just tied to GND and the PG output.

Is the VCC pin on the MP2325 a "bias supply" as TI describe it? What is this VCC pin doing in relation to PG?

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  • \$\begingroup\$ The chip has a internal voltage regulator that converts the voltage at IN to a stable voltage suitable for the chip's own internal operation. This regulated voltage is then brought outside the chip trough pin 7 so it can be properly decoupled with a external capacitor as mentioned in the Pin functions table in the datasheet. \$\endgroup\$
    – Unimportant
    Commented Apr 24, 2022 at 10:33

2 Answers 2

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The \$V_{CC}\$ pin on the MP2325 is brought-out for the externally applied smoothing capacitors. Up to 5 mA can also be drawn from \$V_{CC}\$ for (say) the PG pin: -

enter image description here

The red-lines in the image above are my addition.

Is the VCC pin on the MP2325 a "bias supply" as TI describe it?

No, it is not a pin that should be used this way. \$V_{CC}\$ is generated and used internally by the chip and, it needs external capacitors to smooth it.

What is this VCC pin doing in relation to PG?

enter image description here

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I am TI eng. VCC have no connect with PG PG is Power good signal output. VCC is input to power on the internal circuit. So PG in the output loop. VCC is in input loop.

the "Vcc" in datasheet PG description is point your mcu system power level. like 3.3V, both VCC and Vcc is same word but not a same thing.

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  • \$\begingroup\$ The typical application clearly shows that the PG pull-up resistor is connected to the VCC output. If I understand you correctly, you're saying it should be connected to the external power supply (VIN). But I'm not 100% sure I understand what you're saying. Please clarify. \$\endgroup\$
    – Velvet
    Commented Jun 28, 2023 at 7:36

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