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PDF AN022 Data sheet ( Hoja de datos )
| Número de pieza | AN022 | |
| Descripción | High Side Driver | |
| Fabricantes | AIC | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AN022 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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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 C5
U2 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
February, 2002
Fig. 1 AIC1630A+LDO for P-MOSFET Circuit
1
1 page  
AN022
For example 1:
Min typ max unit
VIN 5
12 V
VOUT
2.5 V
IOUT
0.1
3A
VRIPPLE 50 mV
Assumed that the frequency of operation is 100KHZ,
the forward voltage of sckottky diode is 0.2V and the
switch on voltage of MOSFET is 0.5V. The sequence,
when the switch is on, is calculated as below:
l Selection of inductor
There are many different ways to calculate the
inductance of the required inductor. We can get
easily it from the inductor ripple current ∆IP. When
the minimum loading current is 100mA, the regulator
will operate in continuous–conduction mode. Thus,
the inductor ripple current is calculated as:
TON(MAX)
= DUTY(MAX)
×
T
=
5
2.5 +
− 0.5
0.2
+ 0.2
×
1
120K
=
4.7µs
∆IP = 2IOUT(MIN) = 200mA
Required inductance:
L(MIN)
=
∆VL
∆IP
× ∆T
=
VIN
−
VOUT
∆IP
− VQ
× TON
=
5 − 2.5 − 0.5
200 × 10 −3
×
4.7 × 10 −6
= 47µH
In order to avoid inductor saturation and achieve the
best power efficiency, the material of the inductor
core is recommended to be either in MPP or in iron
powder and also inductance over 47µH should be
applied.
l Selection of capacitor
I. Input capacitor:
The input capacitor is selected mainly on its ESR
value and the RMS current rating, in order to support
high current on an instant at input polarity. Low ESR
capacitors may decrease input ripple and avoid the
disturbance to other circuits in the system. In addition,
a LC filter circuit can improve EMI in the power
system.
II. Output capacitor:
Capacitance and ESR value are two major
considerations for output capacitor. Capacitance
must be able to deliver high loading current when the
switch turns on. And ESR value is a main parameter
in determining the output ripple, transient voltage and
load impedance.
Thus the ESR of output capacitor is calculated as:
ESR =
∆VRIPPLE
∆IP
=
50 ×10 −3
200 ×10−3
= 250mΩ
∆VRIPPLE: desired output ripple voltage
The maximum output peak switch current:
IP(MAX)
=
IO(MAX )
+
∆IP
2
= 3 + 200mA
2
= 3.1A
The minimum capacitor value for a desired output
ripple and load current:
C OUT(MIN )
=
IP(MAX)
8∆VRIPPLE F
=
3.1
8 × 50 × 10 −3 × 120
× 103
= 65µF
l Selection of efficiency
As shown in Fig. 9 and 10 for AIC1630A-2.5V
application, the efficiency of N-MOS circuit is better
than that of P-MOS circuit. Yet, some problems like
MOSFET I2R loss, inductor loss, feedback resistor loss,
output capacitor ESR loss, sckottky diode loss, and
switch loss, which have influence on MOSFET
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet AN022.PDF ] | |
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