AN022 datasheet(3/8 Pages) AIC

3 / 8 page

AN022

AIC1630A with the addition of four external switching

transistors is considered as a buck converter, shown in

Fig.

4. Via EXT (pin3), the internal switching of IC

drives

fast

driving

N-channel

circuit,

which

composed of Q1, Q2, Q3, and Q5. Bootstrapping

circuit (composed of D1, D3, C5 and C7) can provide

N-channel circuit with twice as much as the input

voltage. When Q4 is on, the diode is used as a reverse

biased. Current flows via Q4 as well as the inductor L1

to output polarity. When Q4 is off, the inductor L1

reverses its polarity with its energy transferred to the

output loading, and the diode turns forward biased.

Functions of the bootstrapped driver circuit and driven

N-channel circuit play important roles in the application

of AIC1630A and LDO with N-MOSFET circuit.

3. Bootstrapped Function

As shown in Fig. 5 and 6, the peak rectifier circuit

comprises two diodes

(D1 and D3) and two filter

capacitors (C7 and C5). And the voltage filtered by

peak rectifier may provide control voltage with two

times of VIN dc voltage as shown in Fig. 6 (the lower

waveform). Because the output voltage is boosted up

by a square waveform of amplitude VIN to two times of

the input voltage, the circuit is considered as a

“bootstrapped circuit”.

5V VPULSE

+5V

µF

470

µF

1N5819

10V DC

100

µF

Fig. 5

Bootstrapped Voltage

Fig. 6

Bootstrapped Circuit

Upper: D1 Cathode Polarity Signal

Lower: 10VDC

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