Advanced Analog Technology, Inc
.
May 2008
AAT1168/1168A/1168B
I
Lpeak
DESIGN PROCEDURE
κ =
I
IN
Boost Converter Design
: Boost converter efficiency
η
κ
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 (VOUT1) to GND with the
: The ratio of the inductor peak to peak ripple current
to the input DC current
IN : Input voltage
V
O : Output voltage
V
center tap connected to the IN1. Where V , the boost
IN1
O : Output load current
I
converter feedback regulation voltage is 1.233V.
Choose R2 (Figure 2) between 5.1kΩ to 51kΩ and
calculate R1 to satisfy the following equation.
S : Switching frequency
f
: Duty cycle
D
LPEAK : Inductor peak to peak ripple current
I
IN : Input DC current
I
2
VOUT1
R1 = R
−1
V
IN1
The AAT1168 SW current limit ( LIM ) and inductor’
I
saturation current rating ( LSAT ) should exceed
I
,
I
L(peak)
VOUT1
and the inductor's DC current rating should exceed
.
I
IN
For the best efficiency, choose an inductor with less
DC series resistance (rL ).
VREF
IN1
R1
EO
gm
24
23
VIN1
and
>
IL(peak )
I
I
LIM
LSAT
RC
CC
R2
CP
I
>I
LDC IN
AAT1168/A/B
V D
IN
,
I
= I
+
L
IN
(peak)
2Lf
s
I
O
,
I
=
IN
η(1−D)
Figure 2. Feedback Circuit
2
I
O
P
≈
r
DCR
L
η(1−D)
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
: DC current rating of inductor
ILDC
: Power loss of inductor series resistance
PDCR
Table 1.Inductor Data List
r
C6-K1.8L
DC CURRENT RATING
L
3.9
µ
µ
H
H
2.5A
41 m
Ω
6.8
10
2.2A
1.8A
68 m
81 m
Ω
Ω
µ
H
0.5.
ηV
MITSUMI Product-Max Height: 1.9mm
2
O
,
D(1−D)
L ≥
κI fs
O
Example 1: In the typical application circuit (Figure 1)
the output load current is 300mA with 13.3V output
V
IN
,
D = 1−
V
O
–
–
–
Advanced Analog Technology, Inc. –
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