Low Voltage Step-Down Converter TPS54A20 - Series Capacitor

RE: Low Voltage Step-Down Converter TPS54A20 - Series Capacitor

jc2048 — Sun, 23 Oct 2016 21:31:02 GMT

"This switcher is specific for low voltage designs. The output range is 0.5 - 2 V.

That's a very narrow range."

It might be worth pointing out that that comes (in part) from the theory - it isn't just a limitation of the particular chip. Unlike a simple buck converter, with this circuit configuration the input has to be at least four times the output (if the circuit were perfect) and in practice five times for a real circuit where there are losses. It suits low-voltage POL with a fairly high voltage like 12V at the input, but no-one is going to be using it to drop from 5V to 3.3V.

RE: Low Voltage Step-Down Converter TPS54A20 - Series Capacitor

jc2048 — Sun, 23 Oct 2016 21:20:42 GMT

So it does work as the theory says.

It all looks quite neat and tidy and well controlled. I did wonder - 500nS for the cycle is a fairly short period and the four transistors have to be sequenced carefully to avoid shoot-through of Q1a, Q1b, and Q2b, or shorting the capacitor by having Q1a and Q2a on at the same time. Not sure I'd want to do it discretely and get all the timing right.

My explanation is a bit of a mess.

"...current flows through the capacitor..."? Did I really say that?

It might be better to refer people to the TI application note.

Are you going to have a look at the output ripple next?