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I'm looking for some feedback/validation that the layout for this MCP16301 is correct. I'm trying to get 600mA 3.3v Out from 12 input.

I'm using the circuit as described in the datasheet on page 23 and loosly based on the layout on page 21.

Here's my current PCB layout:

  • Cin - C2/C3 : 4.7uf
  • Rtop - R8: 31.6k
  • Rbot - R9: 10k
  • L1: 15uH
  • Cb - C6: 100nF
  • FW Diode - D4: Diode Schottky 40v
  • Boost Diode - D5: 1N4148
  • Cout - C7/C8: 10uF
  • Reg1: MCP16301

The smaller traces are 10mil and the larger ones are 25mil. enter image description here

REVISED PER COMMENTS(location moved and orientation flipped, but same circuit: Revised Circuit

Revised to larger package D4 SOD123 40v 1A Diodes: enter image description here

Is component placement and routing correct? Anything that I should change? Is the large 3.3Vout pad going to create soldering issues?

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    \$\begingroup\$ I would fatten your current-carrying traces up or switch to polygon fills. Also, there's probably no need for thermals, eliminate those to improve your pad connectivity. \$\endgroup\$
    – uint128_t
    Commented Jun 20, 2016 at 3:52
  • \$\begingroup\$ The data sheet suggests a schottky in a SMA package; this is quite a bit chunkier than the device you have at the moment which appears to have the same dimensions as the boost diode (SOD323 if you use the recommended device). \$\endgroup\$
    – Peter Smith
    Commented Jun 23, 2016 at 8:40
  • \$\begingroup\$ Continuing from my comment above, the schottky needs to be sized according to average current; what is your minimum Vin? \$\endgroup\$
    – Peter Smith
    Commented Jun 23, 2016 at 8:48
  • \$\begingroup\$ Path from Vout to Boost pin (current through boost diode) needs bigger copper area (thicker track). \$\endgroup\$
    – Haris778
    Commented Jun 23, 2016 at 9:26
  • \$\begingroup\$ @PeterSmith average vin is 13.5V \$\endgroup\$
    – GisMofx
    Commented Jun 24, 2016 at 2:10

1 Answer 1

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trace from ground and pin2 need to be more thicker, internal gate current requires a good return pad. Also make sure D4 can drive at least twice load current. if you can improve the thermal dissipation of reg1 adding more cooper under it or bottom layer

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  • \$\begingroup\$ See the revise circuit. I have also found a 1.5a diode for D4. Would this suffice? SOD323 1.5A Diode \$\endgroup\$
    – GisMofx
    Commented Jun 24, 2016 at 21:58
  • \$\begingroup\$ I think board look better but the diode is a little tiny i could not find the Rth(j-a) on the datasheet but I find similar package and is about 415C/W. the forward voltage of diode is about 0.25V at 600mA, so in the worst case you need to dissipate 150mW then the temperature rise of D4 will be 415C/W*0.15= 62C + Tambient good design consider ambient temperature of 60C so I recommend a bigger diode package \$\endgroup\$
    – ise5755
    Commented Jun 25, 2016 at 3:26
  • \$\begingroup\$ Do you think I could use an SOD123 instead of an SMA? \$\endgroup\$
    – GisMofx
    Commented Jun 26, 2016 at 12:55
  • \$\begingroup\$ Consider SOD123FL package with equivalent Electrical characteristics like you selected, forward voltage, capacitance, with current rating same or higher. \$\endgroup\$
    – ise5755
    Commented Jun 26, 2016 at 16:00

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