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I am trying to design a DC to DC UPS using a Li-ion 5000 mAh battery where my load is between 5 V/4 A - 7 A. My system requires keep running after an outage about 20 mins. The load is a RPI3 with extra hardware and a small motor.

My major concern is the in the boost stage, I am looking for any DC-DC step-up/Booster for 7 A+, but I could not find any most are up 4 A.

I tried some solutions from Texas Instruments, Linear Technology and Microchip but no one fit my requirements

Does any one on the past face a similar situation?

I would like use a lead acid battery, but a big size and weight is not option for me.

details:

DC-DC step-up input range 3-4.2V (it is in Li-ion Battery)

DC-DC step-up output: 5V / 1A to 7A

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    \$\begingroup\$ What's the battery voltage and max discharge current? \$\endgroup\$ – Eugene Sh. Aug 25 '17 at 14:14
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    \$\begingroup\$ It would be easier to buy a "charge while use" type of USB power bank? \$\endgroup\$ – user3528438 Aug 25 '17 at 14:15
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    \$\begingroup\$ Split the loads and use multiple 4 amp boosters. \$\endgroup\$ – Andy aka Aug 25 '17 at 14:17
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    \$\begingroup\$ If I fill your requirements and parameters into TI's tool: ti.com/design-tools/webench-power-design/power-designer.html. I get 5 designs from them with IoutMAX ranging from 20-40 A. Here (I am not sure if you can visit this link without TI registration.) \$\endgroup\$ – Bence Kaulics Aug 25 '17 at 14:33
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    \$\begingroup\$ guys thanks a lot, in special Bence and Vince. I think it is solved now. I am going to use a DC-DC boost controller and the TI's tool. This tool is fantastic with the Thermal simulation and recommendations for the layout \$\endgroup\$ – Ale Aug 25 '17 at 17:13
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(Expanding my comment as an answer)

For currents higher than say 3 or 4 Amps, you generally will have to search for Boost "Controller IC" instead of Boost Converter. The difference is that the controller IC has all the logic and smarts but require external MOSFETs.

Currents higher than a few Amps are difficult to handle in the same IC package. By using external MOSFETs, the high currents are handled outside.

Take a look at TI and Linear for higher power stuff and make use of their free design tools (e.g. TI WEBENCH Power Designer, Linear LTPowerCAD and LTSpice).

Keep in mind that there's a big tradeoff: it's now on you to design a good board layout that handles the high currents, minimizes noise coupling, provides good grounding to your IC, keeps the switching noise away from the analog sense lines using separate digital and analog grounds, etc.

If you go this route, make sure you very carefully review the recommended layouts and read the advice in the application notes several times. SMPS layouts that use external MOSFETs are tricky. If you just "wire stuff up" your SMPS will most likely be unstable, run hot, and possibly damage itself and your load.

Also, component selection is very critical. If you're new, then just find an app note that shows an example circuit and use those exact components. If you chose your own components, you will have to learn about inductor saturation, self-resonance, ESR, capacitor ESR and dielectric types, transistor switching speed, gate capacitance, Miller effect, threshold voltage, and then simulate the design taking all that into account! So if you're new and want something quick, scour the datasheets and app notes for a recommended example circuit and use what's already been tested.

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