AN022 Datasheet, PDF (1/8 Pages) Analog Intergrations Corporation – High Side Driver for Buck Converter

AN022
High Side Driver for Buck Converter with an LDO
Introduction
Most boost converters have been applied to step-up
voltage applications, such as the PDA, N/B PC, cellular
phone, palmtop computer, GPS, camcorder, portable
DVD, toy, and DSC, to elevate a low voltage to a high
voltage to provide low quiescent current and high
efficiency regulator in the recent years. Yet, technically,
the boost converter does not supply applications of
high loading current today. Also, the LDO usually can
not transform to a relatively high energy.
AIC1630A is not only a boost converter but also an
application of step-down and a low-dropout function.
The circuit, shown as Fig. 1, can step down from 5V or
12V to as low as 2.5V, 1.8V and 1.25V with 80%
efficiencies. A linear controller can be implemented by
using the pin 6 and 7 of AIC1630A, as shown Fig. 1.
And it works well at low input voltages. For example, a
2.5V input, which comes from the output of AIC1630A,
can be converted into an output of 1.8V. Due to the
ultra-low dropout voltage, the power dissipation is
much lower than the general LDO’s.
Principle of operation
The principle of energy storage in the inductor L can be
applied to the buck converter. And the inductor energy
then is to be transferred to the output via the schootky
diode D. When the switch is on, the diode is used as a
reverse biased and the inductor current will ramp up.
When the switch is off, the inductor reverses its polarity
with a switch current to maintain output voltage.
1. AIC1630A driving P-MOSFET
5V— 12V
+
C1
820µF
R1
1.8K
D3
5.1V
U4
R2
270 _U3
D1
2N2222
1N4148
CEM4435
0.1µF
U2
C5
C4
2N2222 ^680P
36K R3
L1
47µH ⁺
D2
1N5820
U1
1
SD
2 _VIN
3 _EXT
4 _GND
VOUT ⁸
LBI ⁷
LBO ⁶
FB ⁵
AIC1630A
C3
1500µF
R8
2.2
2.5V
R9
1M
U5
D45H2A
1.8V
R4
62K
C6
820PF
R6
9.1K
+
C2
470µF
R5 R7
20K ^20K
Fig. 1 AIC1630A+LDO for P-MOSFET Circuit
February, 2002
1