How can I power an ESP32 with a 54V battery using a buck converter?

Question

I need to power an ESP32 board from a 54 V battery. For that purpose, I understand that I need to step it down to 5 V so I need to design a step-down buck converter.

I tried the following circuit using an LM2576HV as its input range is up to 60 V DC:

I have tried following values of inductor L:

1. 100 μH: when I used a 100 μH inductor and tried to measure output voltage using a multimeter, the IC burned as soon as I supplied 54 V.
2. For an L value of 1000 and 2200 μH the output was 5 V according to the multimeter connected at the output, but when I connected the ESP32 across the output again the IC burned.

• Why did the IC burn?
• Does the capacitor have anything to do with the output current? I understand it is only for output voltage ripple.

I used this diode.

Answer 1

Do you want to design your own step-down converter?

As others pointed out creating huge step-down ratios with the mentioned topology can have numerous pitfalls.

Of course you would learn a lot by designing your own converter. But I wanted to point out you could also focus on the rest of the project instead ;-)

You don't really have to do your own.

Small and proven modules such as R3M or R5M series from Recom might solve the problem. No, I'm not a sales rep for anybody.

Such parts are available from multiple manufacurers, also as SIP and DIP modules. Some also have enable-inputs that may be useful as well if you need to shut-down for any reason.

Answer 2

If you look at the typical application in section 8.2 of the LM2576HV datasheet, where it shows a 5V output design that matches yours, the maximum input voltage for 5V out at 3A is just 15V.

If you scroll down further, to 8.2.1.3 Application Curves, you'll see the operating ranges of input voltage vs. output current and the part codes that are required. Figure 8.5 for the 5V fixed output variant of the device shows that for anything above 15V input you're going to need inductor code H1000 (a 1000uH inductor) and even then you may not exceed around 0.45A draw.

An ESP32 can draw far more than 0.45A when the WiFi transmitter is powered, so this buck converter part is wholly unsuitable for your needs. This isn't really all that surprising - this chip was designed nearly 25 years ago. A more modern buck converter IC should be able to handle this with far greater ease.

EDIT: I misread the datasheet, the above is wrong.

My suspicion is that the efficiency is what's killing your chips. Figure 6-9 shows the efficiency curves vs. input voltage. The efficiency is not very good for 5V out at high input voltages. The efficiency increases with load (this is typical for buck converters) but it doesn't outpace power dissipation. With 54V input, 5V output, and 3A current, you get about 76% efficiency. Your load power is 15W, which means you're putting 19.74W in and dissipating 4.74W in your converter. That's enough to immolate it.

It's possible that your inductor is not suited for the job either - it's not enough to just pick any old 100uH inductor. It needs to at least have appropriate DCR and saturation current ratings.