LM2623 Regulator

I'm implementing a DC/DC regulator and you can find the datasheet in this link.

What I'm trying to do it's basically reproduce the application note in order to have Vin = 12V and Vout = 5V 1Amp but I'm not understanding how do I choose the inductor. They are saying the value for the inductor is 4,7uH but it seems very subjective.

My very first problem is how do I choose the inductor if I don't know which frequency should I select. It seems I can choose something between (300 kHz to 2 MHz) but how do I know which frequency is the best for my case?

Not only that, for the typical application circuit they have put in the datasheet (pag.1) they have a 2 cells for the Vin which I thinks it's something around 7,4V.

Can someone help me on this?

Here is a great load of TI's buck converters.

You can consider this one for example.

• Input voltage range of 3V to 20V
• Output voltage range of 0.8V to 17V
• Output current up to 1A

and the best part for you is the Featured tools and software tab where you can define your parameters and this tool calculates the rest for you.

I did not do a great search, you may find a more suitable converter. It is just a demonstration of the WEBENCH tool which can help you creating your design (not available for all component).

• THanks @battleHamster. I was checking that schematic and it seems ok. There's only a doubt for me which is related with the boost pin. How can i put 5V there if I don't have that Voltage in my design and the pin can only handle 5,5V max. Can you help on that? – scuba May 6 '15 at 11:33
• I have not used this IC before so I know as much as the datasheet says. And it says on page 10that there are four ways to drive this pin. Number 3 is on the schematic above, "from an external distributed voltage rail". But depending on the datasheet you can drive it from the input or the output voltage too. Note that, I just picked one IC from the list as an example, there can be a simplier one for your application. – Bence Kaulics May 6 '15 at 11:46
• This IC could be good too, and I think you can use this setup (also from datasheet). – Bence Kaulics May 6 '15 at 12:02
• Indeed. You helped me a lot. – scuba May 6 '15 at 13:52
• Glad to hear that. :) – Bence Kaulics May 6 '15 at 20:51

What I'm trying to do it's basically reproduce the application note in order to have Vin = 12V and Vout = 5V 1Amp

You have chosen the wrong device. The LM2623 is a boost regulator and not a buck regulator: -

If you want a buck regulator then TI have a good search engine and so do linear tech: -

Entering an input voltage range of 10V to 15V produced 6 hits for 5V at 1A

• Oh Ok my bad. Thanks Andy. But can you recommend me one cheap and easy to implement. – scuba May 6 '15 at 10:41
• Not really but if you find one I can take a look. TI have got loads and a decent parametric engine too. – Andy aka May 6 '15 at 10:42
• @scuba if this question has been answered would you care to "accept" the most appropriate answer. – Andy aka May 28 '15 at 13:38