Advanced Analog Technology, Inc.
April 2007
AAT1164/AAT1164B/AAT1164C
Example 1: In the typical application circuit (Figure 1)
the output load current is 300mA with 13.3V output
voltage and input voltage of 5V. Choose a k of 0.431
and efficiency of 90%.
For example,
PDIODE = PDSW + PDCOM = 0.0273W or 0.68% power loss.
Input Capacitor Selection
The input capacitors have two important functions in
PWM controller. First, an input capacitor provides the
power for soft start procedure and supply the current for
the gate-driving circuit. A 10 µF ceramic capacitor is
used in typical circuit. Second, an input bypass
capacitor reduces the current peaks, the input voltage
drop, and noise injection into the IC. A low ESR
ceramics capacitor 0.1µF is used in typical circuit. To
ensure the low noise supply at VDD, VDD is decoupled
from input capacitor using an RC low pass filter.
0.9 *13.3
0.431* 0.3 *1.26
6.8µH
L ≥
0.624(0.376)2
≈
I
O
I
=
= 0.886A
IN
η(1− D)
V D
IN
I
= I +
IN
= 1.0778A
L(peak)
2Lf
S
PDCR = 0.0534W or 1.34% power loss
Schottky Diode Selection
Schottky has to be able to dissipate power. The
dissipated power is the forward voltage and input DC
current. To achieve the best efficiency, choose a
Schottky diode with less recovery capacitor (CT) for fast
recovery time and low forward voltage (VF).
For boost converter, the reverse voltage rating (VR)
should be higher than the maximum output voltage, and
current rating should exceed the input DC current.
VDD
VDD
PDIODE = PDSW + PDCOM
PDSW = (1–D) VFQRfS
QR = VRCTQR
Figure 3. Input Bypass Capacitor Affects the VDD
Drop.
PDCOM = VFIO (1–D)
Output Capacitor
The output capacitor maintains the DC output voltage. A
PDIODE: Total power loss of diode for boost converter
PDSW: Switching loss of diode for boost converter
PDCOM: Conduction loss of diode for boost converter
r
Low ESR ( C ) ceramic capacitor can reduce the output
ripple and power loss. There are two parameters which
can affect the output voltage ripple: 1. the voltage drops
when the inductor current flows through the ESR of
output capacitor; 2. charging and discharging of the
Table 2. Schottky Data List
SMA
VF
VR
CT
B220A
B240A
0.24V
0.24V
14V
28V
150pF
150pF
output capacitor also affect the output voltage ripple.
VRIPPLE = VRIPPLE (COUT ) + VRIPPLE (ESR)
DIODES Product-Max Height: 2.3mm
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Advanced Analog Technology, Inc
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