AAT1230/1230-1
18V 100mA Step-Up Converter
10000
1000
100
Selecting the Boost Inductor
B340LA
The AAT1230/1230-1 controller utilizes hysteretic
control and the switching frequency varies with
output load and input voltage. The value of the
inductor determines the maximum switching fre-
quency of the AAT1230/1230-1 boost converter.
Increased output inductance decreases the switch-
ing frequency, resulting in higher peak currents and
increased output voltage ripple. To maintain 2MHz
maximum switching frequency and stable opera-
tion, an output inductor sized from 1.5µH to 2.7µH
is recommended.
MBR0530
ZHCS350
BAT42W
10
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Forward Voltage (V)
The average diode current is equal to the output
current.
A better estimate of DMAX is possible when VF is
known.
IAVG(TOT) = IOUT
(VOUT + VF - VIN(MIN)
(VOUT + VF)
)
DMAX
=
The average output current multiplied by the for-
ward diode voltage determines the loss of the out-
put diode.
Where VF is the Schottky diode forward voltage. If
not known, it can be estimated at 0.5V.
Manufacturer’s specifications list both the inductor
DC current rating, which is a thermal limitation, and
peak inductor current rating, which is determined
by the saturation characteristics. Measurements at
full load and high ambient temperature should be
completed to ensure that the inductor does not sat-
urate or exhibit excessive temperature rise.
PLOSS(DIODE) = IAVG(TOT)
= IOUT VF
· VF
·
Diode junction temperature can be estimated.
The output inductor (L) is selected to avoid satura-
tion at minimum input voltage, maximum output load
conditions. Peak current may be estimated using
the following equation, assuming continuous con-
duction mode. Worst-case peak current occurs at
minimum input voltage (maximum duty cycle) and
maximum load. Switching frequency can be estimat-
ed from the curves and assumes a 2.2µH inductor.
TJ(DIODE) = TAMB + ΘJA · PLOSS(DIODE)
Output diode junction temperature should be
maintained below 110ºC, but may vary depending
on application and/or system guidelines. The
diode θJA can be minimized with additional PCB
area on the cathode. PCB heatsinking the anode
may degrade EMI performance.
2.0
VIN = 3.0V
VOUT = 18V
VIN = 3.0V
VOUT = 15V
The reverse leakage current of the rectifier must be
considered to maintain low quiescent (input) cur-
rent and high efficiency under light load. The recti-
fier reverse current increases dramatically at high
temperatures.
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
VIN = 3.6V
VOUT = 18V
VIN = 3.6V
VOUT = 15V
VIN = 2.7V VIN = 2.7V
VOUT = 18V VOUT = 15V
40
50 60
70
80
90
100
Output Current (mA)
1230.2006.10.1.4
11
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