AAT1168-Q5-T AAT [Advanced Analog Technology, Inc.], AAT1168-Q5-T Datasheet - Page 15

• Manufacturer Part Number: AAT1168-Q5-T
• Description: TRIPLE-CHANNEL TFT LCD POWER SOLUTION WITH OPERATIONAL AMPLIFIERS
• Manufacturer: AAT [Advanced Analog Technology, Inc.]

voltage and input voltage of 5V. Choose a
and efficiency of 90%.
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 (V
should be higher than the maximum output voltage,
and current rating should exceed the input DC current.
For example,
L
I
I
P
P
P
P
P
P
P
P
Q
IN
( L
Table 2. Schottky
DCR
DIODE
DSW
DCOM
DIODE
DSW
DCOM
DIODE
R
peak
. 0
= 0.043W or 1% power loss
465
: Switching loss of diode for boost converter
(1 D)
V
)
I
: Conduction loss of diode for boost converter
: Total power loss of diode for boost converter
0
R
O
=
B220A
B240A
=
DIODES Product, Max-Height: 2.3mm
9 .
SMA
C
V
P
*
I
IN
T
F
DSW
1 (
P
*
0
I
DSW
13
O
= 0.89A
3 .
D
/(
3 .
*
V
2
1
1
V )
IN
Lf
1 .
P
F
D
P
D
DCOM
s
6
Q
DCOM
)
D D D D
. 0
= 1.095A
R
a ta
f
624
s
= 0.203W or 5.1% power loss.
0.24V
0.24V
L L L L
(
V
Advanced Analog Technology, Inc
. 0
i st
F
376
)
2
14V
28V
V
6.8 H
R
–
150pF
150pF
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–
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of 0.465
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Page 15 of 22
Version 1.00
R
)
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 F 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 0.1 F is used in typical circuit. To
ensure the low noise supply at
from input capacitor using an RC low pass filter.
Figure 3. Input Bypass Capacitor Affects the
Drop
Output Capacitor
The output capacitor maintains the DC output voltage.
A Low ESR (
output
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 output capacitor also affect the
output voltage ripple.
V
V
V
RIPPLE
RIPPLE
RIPPLE
(ESR) I
(
ripple
C
–
OUT
V
RIPPLE
)
r
C
L(peak) C
AAT1168/1168A/1168B
and
.
) ceramic capacitor can reduce the
f
(
S
C
C
I
O
OUT
OUT
power loss. There are two
D
r
)
V
RIPPLE
V
DD
(
,
ESR
V
DD
)
is decoupled
May 2008
V
DD