AAT1168 Datasheet, PDF (14/22 Pages) Advanced Analog Technology, Inc. – TRIPLE-CHANNEL TFT LCD POWER SOLUTION WITH OPERATIONAL AMPLIFIERS

Advanced Analog Technology, Inc.
May 2008
AAT1168/1168A/1168B
DESIGN PROCEDURE
Boost Converter Design
Setting the Output Voltage and Selecting
the Lead Compensation Capacitor
The output voltage of boost converter is set by the
resistor divider from the output (V_OUT1) to GND with the
center tap connected to the IN1. Where V_IN1, the boost
converter feedback regulation voltage is 1.233V.
Choose R₂ (Figure 2) between 5.1kΩ to 51kΩ and
calculate R₁ to satisfy the following equation.
R₁
=
R₂



V_OUT1
V_IN1

− 1_

V_OUT1
R_C
C_P
C_C
EO
24
VREF
gm
IN1
23
AAT1168/A/B
R₁
V_IN1
R₂
Figure 2. Feedback Circuit
Inductor Selection
The minimum inductance value is selected to make
sure that the system operates in continuous conduction
mode (CCM) for high efficiency and to prevent EMI.
The equation of inductor used a parameter κ , which is
the ratio of the inductor peak to peak ripple current to
the input DC current. The best trade-off between
voltage ripple of transient output current and
permanent output current has a κ between 0.4 and
0.5.
L ≥ ^ηVO D(1− D)^{2 ,}
κI_Ofs
D = 1− ^{VIN ,}
V_O
κ = ^ILpeak
I_IN
η : Boost converter efficiency
κ : The ratio of the inductor peak to peak ripple current
to the input DC current
V_IN : Input voltage
V_O : Output voltage
I_O : Output load current
f_S : Switching frequency
D : Duty cycle
I_LPEAK : Inductor peak to peak ripple current
I_IN : Input DC current
The AAT1168 SW current limit ( I_LIM ) and inductor’
saturation current rating ( I_LSAT ) should exceed I_{L(peak )} ,
and the inductor's DC current rating should exceed I_IN .
For the best efficiency, choose an inductor with less
DC series resistance ( r_L ).
I_LIM and I_LSAT > I_{L(peak )}
I_LDC > I_IN
I_{L(peak )}
= I_IN
+
V_IND
2Lf_s
,
I_IN
=
I_O
η(1− D)
,
P_DCR
≈



I_O
η(1− D)
²


r_L
I_LDC : DC current rating of inductor
P_DCR : Power loss of inductor series resistance
C6-K1.8L
3.9 µH
Table 1.Inductor Data List
r_L
DC CURRENT RATING
41 m Ω
2.5A
6.8 µH
10 µH
68 m Ω
81 m Ω
2.2A
1.8A
MITSUMI Product-Max Height: 1.9mm
Example 1: In the typical application circuit (Figure 1)
the output load current is 300mA with 13.3V output
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