AAT1164 Datasheet, PDF (20/24 Pages) Advanced Analog Technology, Inc. – TRIPLE-CHANNEL TFT LCD POWER SOLUTION

Advanced Analog Technology, Inc.
April 2007
AAT1164/AAT1164B/AAT1164C
OUT3 26
IN3 25
VOUT3 1
SW
C5
1µF
C6
1µF
R4
6.8k Ω
U1
BAT54S
Q1
MMBT 4403
V_OUT1
13.3V/300mA
C7
1µF
SW
R5
200 k Ω
R6
10kΩ
C8
1µF
U2
BAT54S
V_OUT3
25V/30mA
Figure 8. The Positive LDO Driver
used. BAT54S (Figure 8 and 9) has fast recovery time
and low forward voltage for best efficiency.
LDO Driver Base-Emitter Resistors
For AAT1164, the minimum drive current for positive
and negative LDO drivers are 1mA, thus the minimum
base-emitter resistance can be calculated by the
following equation:
R_4(min) ≥ V_BE(max) / ((I_OUT3(min) − I_C ) / h_fe(min) )
R_7(min) ≥ V_BE(max) / ((I_OUT2(min) − I_C ) / h_fe(min) )
Table 4. Pass Transistor Specifications
MMBT4401
MMBT4403
V_BE(max)
0.65V
0.5V
h_fe(min)
130
90
DIODES Product, Package: SOT23
Example 5:
Output current of V_OUT3 and V_OUT2 are 30mA, the
minimum base-emitter resistor can be calculated as
Figure 9. The Negative LDO Driver
Example 4:
For system design
R_4(min) ≥ 0.5 / (( 1mA − 30mA ) / 90) ≥ 750 Ω
R_7(min) ≥ 0.65 / (( 1mA − 30mA ) / 130) ≥ 845 Ω
V_OUT3 = 25V, R₅ = 200kΩ, R₆ = 10kΩ,
V_OUT2 = −6V, R₈ = 62kΩ, R₉ = 10kΩ
Flying Capacitors
Increasing the flying capacitor (C₅, C₇, C₉) values 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
The minimum value can be used, however, the larger
value has the advantage of reducing quiescent current.
So we choose 6.8kΩ to be R₄.
Charge Pump Output Capacitor
Using low ESR ceramic capacitor to reduce the output
voltage ripple is recommended and output voltage ripple
is dominated by the capacitance value. The minimum
capacitance value can be calculated by the following
equation:
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