As shown in the picture, the picture shows the internal block diagram of the commonly used BUCK chip.
There are three questions for you: 1. The bootstrap capacitor between BST and SW is generally 0.1uF. Is this value an empirical value or how did it get it?
2. The way to charge the bootstrap capacitor is to charge it through a diode through VCC. Isn't the instantaneous current very large when the capacitor is charged? Will it burn out the diode? Do you need to connect the bootstrap capacitor in series with current limiting? Resistance, how much resistance in series?
3. If the upper tube and lower tube are externally installed, can the same model of Nmos tube be selected, that is, the parameters are the same, what should I pay attention to when choosing?
Erin Posted on December 4, 2020
This is the bootstrap capacitor, used to power the driver,,,
Cooper Posted on December 4, 2020
The diode is inside the IC, and there is no resistance in series.
If it is connected to the outside, it is not connected to the diode.
Kylie Posted on December 4, 2020
0.1uF should be an empirical value, if you want to calculate it, you can also calculate a value. As for the current-limiting resistor you mentioned, it is definitely not enough. The general switching frequency is high. Adding a current-limiting resistor affects the charging time.
