12V->5V @ 3A Buck Converter Board

Owned by Nolan Haines
Last updated: 2024-06-04 by Daniel Puratich
3 min read

Status: Produced

Designer: @Nolan Haines

Reviewer: @Daniel Puratich

User Advisory: RCA: Fried LED Boards

 

Initial Requirements:

12V-5V @ 3A Buck Converter Board -

  • 12V-5V Synchronous Buck Converter PCB @ 3A Max Load Current Consumption (15W)

  • I/O:

    • Input Voltage Connector

      • +12V

      • GND

    • Output Voltage Connectors (2x)

      • +5V

      • GND

    • Current Sense Connector

      • V_sense+ and V_sense-, or:

      • I_sense and GND

  • Features:

    • 12V-5V Buck Converter @ 3A

    • Reverse Polarity Protection

    • Status LEDs for both +12V and +5V voltage rails

    • Optional current sense interface

Documentation:

 

 

 

*NOTE: The numbers for the components below does not correlate with the typical application circuit above. Please refer to the altium schematic for this board for the correct numbering.

Capacitors:

C1, C2, C5, C6, C7, C8, C9, C10: https://www.digikey.ca/en/products/detail/murata-electronics/GRM188R61E106KA73J/9887674

Voltage rating is 25V which will suffice for this application as the maximum will be 12V. We want a voltage rating of 2 to 3 times the voltage at the node. In the datasheet they recommend C1 to be 10uF for any application of this IC.

C3 & C4: https://www.digikey.ca/en/products/detail/samsung-electro-mechanics/CL10B104KA8NNNC/3886664 

Voltage rating is 25V which will be more than enough for this application. It will be able to handle the high voltage (12V). Moreover this is what the datasheet recommends.

Bulk Capacitor:

  • Used to stabilize output voltage in switching regulators. If the output voltage drops suddenly, the bulk capacitor will be there to compensate until the regulator is able to react and adjust itself.

  • Typically of a much larger value than decoupling caps.

Decoupling Capacitor:

  • Reduces noise by sending it to ground.

  • Physically as close as possible to the IC pins, since putting them further away will reduce noise reduction accuracy.

  • Can be used to isolate different circuits as capacitors block DC current.

  • Can be used to provide pure DC to a circuit or IC (eg. have a decoupling cap in parallel with load and tied to ground. AC will go to ground while DC will pass onto the load).

  • Can be used in a similar capacity in order to separate AC and DC signals.

Source:

De-coupling capacitor and Bulk capacitor

C8 & C9: https://www.digikey.ca/en/products/detail/samsung-electro-mechanics/CL21A226KOQNNNG/3894433

The capacitance value for C8 and C9 is 22uf each, adding up to 44uf. We chose this value because it is compliant with the datasheet as the capacitance total for C8 & C9 should be 20<x<68. These are bulk capacitors, which were described above.

  • These act as bulks caps as the magnetic field created from the inductor will store energy and is used to provide a safety net of current once charged to prevent the output supply to drop or increase when current is not available.

Resistors:

R1: https://www.digikey.ca/en/products/detail/yageo/RC0603FR-0754K9L/727298

Reasoning is in the table of the datasheet. For an output voltage of 5V, they recommend the resistance to be 54.9k ohm.

 

R2: https://www.digikey.ca/en/products/detail/yageo/RC0603DR-0710KL/5917797

Reasoning is in the table of the datasheet. As R2 is connected to VBF which is the pin for the converter feedback input. Moreover, the datasheet recommends 10K resistors for all types of application for this IC.

 

R1 & R2 are part of the voltage divider in the feedback circuit, used to set the output voltage. Their values can be tweaked to change the voltage send to VFB. The voltage sent to VFB is the desired output voltage.


R3: https://www.digikey.ca/en/products/detail/yageo/RC0603DR-0710KL/5917797

This is a current limiting resistor and it must remain active high and has to be pulled up to enable the device.

Inductor:

 

L1: https://www.digikey.ca/en/products/detail/würth-elektronik/78438357047/8134316

For an output voltage of 5V, the datasheet recommends using an inductance value of 3.3-4.7 uH. A higher inductor value will result in a lower peak-to-peak ripple current (equation 4 of the IC datasheet), and thus the highest value within the range was selected. Moreover the inductor we selected has a current rating of 3.9A and the IC has a current rating of 3A so having 3.9A for the inductor should have some buffer room in case there is an increase in current.

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