DCDC buck converter output capacitor placement

I have a microprocessor with built in DCDC converter. We need to provide in ductor and output capacitors externally at the respective pins of the proce ssor. The regulated o/p from the internal DCDC converter is for internal co re and IO as well as for external peripherals. The manufacturer recommends using 0.01uf, 0.1uf, 1uf and 33uf at the DCDC output pin. What should be th e order of placement of these o/p capacitors on the board? 0.01uf close to the pin and 33uf away or the other way? The current from the o/P pin is bot h ways. i.e goes internal to the IC as well as goes out of the pin to the o ther peripherals on the board.

-bjnk

Reply to
bhav.jnk
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Smallest capacitance closest to the pin. But nowadays a 0.1uF in 0603 package is good enough, there is usually no need for an extra 0.01uF. The 1uF is debatable, may not be needed if the 33uF is a ceramic.

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Regards, Joerg 

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Reply to
Joerg

inductor and output capacitors externally at the respective pins of the processor. The regulated o/p from the internal DCDC converter is for internal core and IO as well as for external peripherals. The manufacturer recommends using 0.01uf, 0.1uf, 1uf and 33uf at the DCDC output pin. What should be the order of placement of these o/p capacitors on the board? 0.01uf close to the pin and 33uf away or the other way? The current from the o/P pin is both ways. i.e goes internal to the IC as well as goes out of the pin to the other peripherals on the board.

That sounds like overkill. I'd go for 2x15uF ceramics. The node should be a big copper pour, adjacent to the ground plane. Another cap, 330 nF or some such, near each peripherial chip wouldn't hurt, but don't overdo it.

What uP is it? Built-in buck converters are uncommon.

Reply to
John Larkin

inductor and output capacitors externally at the respective pins of the pr ocessor. The regulated o/p from the internal DCDC converter is for internal core and IO as well as for external peripherals. The manufacturer recommen ds using 0.01uf, 0.1uf, 1uf and 33uf at the DCDC output pin. What should be the order of placement of these o/p capacitors on the board? 0.01uf close to the pin and 33uf away or the other way? The current from the o/P pin is both ways. i.e goes internal to the IC as well as goes out of the pin to th e other peripherals on the board.

I wonder why?

I remember working a zigbee chip years ago, it had an on-chip LDO since it the chip was 1.8V and usually it would run on a ~3V battery

everyone looked at me funny when I suggested adding a buck converter, it was really only a matter of adding a switch on chip and an external coil and diode it didn't have to be very accurate and in sleep mode where the chip only used uA the switch could just be permanently on since it would be feeding the LDO

I know it got put in, but I don't know how well it worked

-Lasse

Reply to
langwadt

Thanks. Its i.mx23 from freescale.

Reply to
bhav.jnk

Does the manufacturer not provide an app note with a recommended layout? Often (I want to say "usually" but can't) a microprocessor will provide layout notes for "analog-y" parts of a circuit, such as oscillator pins and (presumably) regulator pins.

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Reply to
Tim Wescott

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