AAT1168-Q5-T AAT [Advanced Analog Technology, Inc.], AAT1168-Q5-T Datasheet - Page 19

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

Example 4:
For system design
V
V
Flying Capacitors
Increasing the flying capacitor (
can lower output voltage ripples. The 1µF ceramic
capacitors works well in positive LDO driver. A 0.1µF
ceramic capacitor works well in negative LDO driver.
LDO Driver Diode
To achieve high efficiency, a Schottky diode should be
used. BAT54S (Figure 8 and 9) has fast recovery time
and low forward voltage for best efficiency.
LDO Driver Base-Emitter Resistors
For AAT1168, the minimum drive current for positive
and negative LDO driver are 1mA, thus the minimum
base-emitter resistance can be calculated by the
following equation:
R
R
OUT3
OUT2
4
7
(min)
(min)
= 25V,
= −6V,
Figure 9. The Negative LDO Driver
V
V
BE
BE
R = 200k
R = 62k
(max)
(max)
5
8
/((
/((
I
I
OUT
OUT
,
2
3
Advanced Analog Technology, Inc
,
(min)
R = 10k
(min)
R = 10k
9
6
I
I
C
C
C ,
/ )
/ )
5
hfe
hfe
C ,
,
7
(
(
–
min
min
C ) values
)
)
Advanced Analog Technology, Inc. –
9
–
)
)
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Page 19 of 22
Version 1.00
Example 5:
Output current of V
minimum base-emitter resistor can be calculated as
The minimum value can be used, however, the larger
value has the advantage of reducing quiescent current.
So we choose 6.8k
Charge Pump Output Capacitor
Using low ESR ceramic capacitor to reduce the output
voltage ripple is recommended. With ceramic capacitor,
output voltage ripple is dominated by the capacitance
value. The minimum capacitance value can be
calculated by the following equation:
Example 6:
The output voltage ripple of V
the minimum capacitance value can be calculated as
R
R
Cout
Cout(V
Cout
7
4
: Efficiency, about 60% at charge pump circuit
(min)
(min)
(
V
V
hfe
Table 4 Pass Transistor Specifications
OUT3
GL
BE
2
V
–
(min)
(max)
. 0
I
)
0
ripple
load
5 .
DIODES Product, Case: SOT23
65
)
/((
/((
2
f
s
1
AAT1168/1168A/1168B
2 250mV 1.19MHz
mA
1
.
mA
60
OUT3
mV
30
to be R
30
and V
30mA
mA
30
MMBT4401
mA
. 1
mA
0.65V
19
130
4
/ )
OUT3
OUT2
.
/ )
MHz
90
130
)
are 30mA, the
and VGL is under 1%,
)
750
0.33µF
845
0.1µF
MMBT4403
0.5V
90
May 2008