Please answer my question: What is the role of capacitor in this synchronous buck circuit?

灞波儿奔

Please answer my question: What is the role of capacitor in this synchronous buck circuit? [Copy link]

We often see such a capacitor in the circuit of synchronous buck IC, such as capacitor C in the red box in the figure below. Why is there such a capacitor here?

What is the function?

I beg the great god to answer my questions

dcexpert

Taking TPS5430 as an example, the description of BOOT in the document is as follows:

Connect a 0.01 F low-ESR ceramic capacitor between the BOOT pin and PH pin. This capacitor provides the gate drive voltage for the high-side MOSFET. X7R or X5R grade dielectrics are recommended due to their stable values over temperature.

Connect a 0.01F low ESR ceramic capacitor between the BOOT pin and the PH pin. This capacitor provides the gate drive voltage for the high-side MOSFET. It is recommended to use X7R or X5R grade dielectrics because of their stable values over temperature.

maychang

"Why is there such a capacitor here?"

This is the so-called "bootstrap" capacitor. Refer to the Buck circuit composed of discrete components. The Buck circuit composed of discrete components, diodes and MOS tubes are all built into the chip, but this capacitor cannot be built into the chip and must be connected externally.

Gen_X

The above comments are all correct. In some places, it is also called a boost capacitor, which is used to boost or provide bias for internal drivers.