AAT1164 Datasheet, PDF (16/24 Pages) Advanced Analog Technology, Inc. – TRIPLE-CHANNEL TFT LCD POWER SOLUTION

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%.
L ≥ ^{0.9 * 13.3} 0.624(0.376)² ≈ 6.8 µH
0.431* 0.3 * 1.2⁶
I_IN
=
I_O
η(1− D)
=
0.886A
I_{L(peak )}
= I_IN
+
V_IND
2Lf_S
=
1.0778A
P_DCR = 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 (C_T) for fast
recovery time and low forward voltage (V_F).
For boost converter, the reverse voltage rating (V_R)
should be higher than the maximum output voltage, and
current rating should exceed the input DC current.
P_DIODE = P_DSW + P_DCOM
P_DSW = (1–D) V_FQ_Rf_S
Q_R = V_RC_TQ_R
P_DCOM = V_FI_O (1–D)
P_DIODE: Total power loss of diode for boost converter
P_DSW: Switching loss of diode for boost converter
P_DCOM: Conduction loss of diode for boost converter
SMA
Table 2. Schottky Data List
V_F
V_R
C_T
B220A
0.24V
14V
150pF
B240A
0.24V
28V
150pF
DIODES Product-Max Height: 2.3mm
For example,
P_DIODE = P_DSW + P_DCOM = 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 0.1 µF is used in typical circuit. To
ensure the low noise supply at V_DD, V_DD is decoupled
from input capacitor using an RC low pass filter.
VDD
VDD
Figure 3. Input Bypass Capacitor Affects the V_DD
Drop.
Output Capacitor
The output capacitor maintains the DC output voltage. A
Low ESR ( r_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
output capacitor also affect the output voltage ripple.
V_RIPPLE = V_RIPPLE (C_OUT ) + V_RIPPLE (ESR)
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