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LM2576HVSX-12 Understanding

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Ryan St. John 4 years ago

Hello all, I am trying to buck down 48V to 12V so that I can supply an ESP32 (the ESP32 uses a AMS1117 regulator onboard: [Link](http://www.advanced-monolithic.com/pdf/ds1117.pdf)). I am trying to use a LM2576HVSX-12 as I believe this should do the job ([Datasheet](https://datasheet.lcsc.com/szlcsc/1810111012_Texas-Instruments-LM2576HVSX-12_C38021.pdf)). Page 19 shows an example for sizing the components, but it seems that I need a 220uH inductor rated at 3.45A for a 3A at 48V outout. I don't think I will be able to find anything like this. Am I making a mistake with the calculations or misinterpreting something? Please excuse my naivety. Thank you!

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Comments

andyfierman 4 years ago

Do you really need a 3A output capable smps? The LM2576HVSX-12 datasheet does not mention it but the smps may need a minimum load current for it to maintain a regulated 12V output.

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Ryan St. John 4 years ago

@andyfierman Hey Andy, That is a good point, I don't specifically need a smps. Really I am just looking for a 48VDC to ~12VDC power supply that will power the ESP32 up to 3A. Perhaps I should look into other types of supplies as you hint at. Do you have any suggestions?

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andyfierman 4 years ago

If you really need up to 3A then the device you've selected is OK as long as you can design in some way of ensuring you either draw the minimum load (whatever that turns out to be or you can allow the LM2576HVSX-12 output rising at sub-minimum load currents. I will supply some sums for the inductor (and maybe other parts) later. Bit busy at the moment. Can you post a written spec for input voltage min & max, output voltage min & max, load current min & max, allowable pk-pk voltage ripple on Vout, allowable max current in output short circuit conditions, limits on input startup current?

Chrome 85.0.4183.83 Windows 10 EasyEDA 6.4.5

Ryan St. John 4 years ago

@andyfierman Hey Andy, I tried the [WEBENCH® POWER DESIGNER ](https://webench.ti.com/power-designer/) from TI and this is one of the solutions it recommended to me for power my ESP32 with 5V at 2A. This seems to be the simplest of the circuits with the smallest footprint, which is really what I am after. The 2A should be plenty to keep the ESP32 from browning out, and the 5V will feed the ASM117 nicely. Do you have any comments or recommendations? This is the correct placement of the ESP32, correct? I replaced the Iout node with the ESP32. ![Circuit.png](//image.easyeda.com/pullimage/TN4U8GAn8XvWuzxqJ9MOQf8ikJWPX2koudVm1tps.png) Thank you!

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