MB3789 datasheet(21/28 Pages) FUJITSU

Part #	MB3789

Description	Switching Regulator Controller (Supporting External Synchronization)

PDF	28 Pages

Scroll/Zoom	100%

Manufacturer	FUJITSU [fujitsu semiconductor]

Direct Link

Logo

21 / 28 page

MB3789

Operation of the Bootstrap Capacitor

When voltage VOUT at the OUT pin (pin 15) is “L” level, the voltages (VC1) at both ends of the bootstrap capacitor

CBS is charged up to the VCC2 voltage level by charge current (iC).

When VOUT changes from “L” level to “H” level, the CB pin (pin 13) voltage VCBS rises to

× VCC2 and VOUT

reaches almost the VCC2 level.

The charge accumulated at CBS at this time is released by discharge current id (output unit supply current).

See Figure 12 for circuit operation.

20406080

100

tON

tOFF

2 V

µs

Time t (

µs)

(VCC1 = 5 V, VCC2 = 6 V, CBS = 4700 pF)

VCBS*1

VOUT

*1: Use the device with a setting of VCBS

18 V.

*2: The slant of VCBS is determined by the value of discharge current id (output unit supply current).

Figure 14 Bootstrap operating waveform

MB3789 Datasheet(PDF) 21 Page - fujitsu semiconductor