AAT1187A Advanced Analog Technology, Inc., AAT1187A Datasheet - Page 18

• Manufacturer Part Number: AAT1187A
• Description: Boost Converter For Wled Driver
• Manufacturer: Advanced Analog Technology, Inc.

DESIGN PROCEDURE
Boost Converter Design
Inductor Selection
The minimum inductance value, resistance of the
resistors in series connection, and peak current rating
are
efficiency.
The minimum value of inductor is selected to ensure
that the system operates in continuous conduction
mode
performance. The equation of inductor selection uses a
parameter ĸ, which is the ratio of peak to peak ripple
current of the inductor to the input DC current. The best
trade-off between voltage ripple of transient output
current and permanent output current has a κ between
0.2 and 0.4.
ŋ: Boost Converter Efficiency
ĸ: Ratio of the Inductor Peak-to-Peak Ripple Current
V
V
I
f
D: Duty Cycle
∆I
I
The AAT1187A SW current limit (I
saturation current rating (I
and the inductor's DC current rating should exceed I
For optimal efficiency, choose an inductor with less DC
resistance (r
I
L
O
S
IN
LIM
IN
O
: Switching Frequency
: Output Load Current
Lpeak-peak
: Input DC Current
: Output Voltage
and the Input DC Current
: Input Voltage
κI f
and I
ηV
O S
important
O
(CCM)
D(1 D)
LSAT
: Inductor Peak-to-Peak Ripple Current
L
> I
). ESR DSR DCR
2
L(peak)
,
for
D 1
factors
high
Advanced Analog Technology, Inc.
V
V
IN
O
LSAT
that
,
efficiency and EMI-free
κ =
) should exceed I
∆I
influence
Lpeak-peak
LIM
I
IN
) and inductor’s
–
–
Advanced Analog Technology, Inc . –
converter
台 灣 類 比 科 技 股 份 有 限 公 司
L(peak)
Page 18 of 28
Version 1.00
IN
,
.
I
I
P
Example: In the typical application circuit, output load
current is 200mA with 8.6V output voltage and input
voltage of 3.3V. Choose a ĸ of 0.3 and efficiency of
90%
P
I
I
L
I
I
LDC
L(peak)
IN
LDC
IN
L(peak)
DCR
DCR
C6-K1.8L
: DC Current Rating of Inductor
> I
10.0µH
0.3 0.2 (1.2)
.
: Power Loss of Inductor Resistance
3.9µH
6.8µH
η(1 D)
= 0.0272W or 1.58% power loss
η(1 D)
IN
I
I
0.9 8.6
O
O
MITSUMI Product-Max Height: 1.9mm
I
IN
–
I
IN
,
= 0.579A
Table 1. Inductor Data List
V D
2Lf
IN
P
V D
2Lf
DCR
S
IN
41m
68m
81m
,
s
6
r
= 0.664A
L



0.6163 (0.3837)
η(1 D)
I
O
DC CURRENT RATING



2
r
L
AAT1187A
2.5A
2.2A
1.8A
2
September 2009
10 H