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I am working on a design featuring the MP1495S switching regulator. The regulator will take 12V and output 5V. The maximum current I want to allow at the output of the regulator is 3A.

1) I am correct in thinking that this implies a max current of 1.25A at 12V at the input?

2) I want to protect the input of the regulator using a PTC and a TVS, and need help selecting the correct ones. Would the 0ZCG0260FF2C combined with the SMBJ12A work?

I looked at the electrical characteristics of 0ZCG0260FF2C but I don't fully understand how the rated voltage relates to the trip and hold current. They mention "rated current", so they probably mean trip current?

EDIT: I realized I probably need a bidirectional TVS so I also protect against reverse voltage, so I should probably use the SMBJ12CA instead?

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  1. No, You'll need slightly more input power than output power. It depends on the efficiency of the converter as a whole. For example if it has an efficiency of say 90%, then you'll need about 1.4A at 12V (16.8W) at the input to get 5V 3A (15W) at the output. The extra power is used by the components to carry out the conversion, there would also be loses due to heat. That's why you would want to select an inductor with as low a DCR (direct current resistance) as possible and MOSFETS with as low an Rdson and gate charge (getting both low usually leads to more expensive devices) as possible (in your case with this controller, the MOSFETS are embedded so no choice to be made).

  2. For me, I would just follow the typical application circuit that some manufacturers are nice enough to give. Your IC has one on page 15 of the datasheet that shows a circuit for your requirements of 5v 3A output. You could just go with that.

(On a side note these guys are pretty great for showing so many different circuits for different output options, I don't usually see that many!).

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  • \$\begingroup\$ thanks, I'm already following the 12V in/5V out example from the MP1495S datasheet. What I need help with is in selecting the right fuse (PTC) and TVS to protect the input of the MP1495S. \$\endgroup\$ – b20000 Sep 22 '17 at 20:12
  • \$\begingroup\$ Page 1 of the datahseet for the MP1495S says "Full protection features include over-current protection and thermal shut down.". I don't really think you need a PTC after that. As for the TVS, that looks like it would work fine. \$\endgroup\$ – Alaba Baju Sep 22 '17 at 21:10

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