AAT1230 Datasheet, PDF (11/21 Pages) Advanced Analogic Technologies – 18V 100mA Step-Up Converter

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B340LA
MBR0530
ZHCS350
BAT42W
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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.
I_AVG(TOT) = I_OUT
The average output current multiplied by the for-
ward diode voltage determines the loss of the out-
put diode.
P_LOSS(DIODE) = I_AVG(TOT) · V_F
= I_OUT · V_F
Diode junction temperature can be estimated.
T_J(DIODE) = T_AMB + Θ_JA · P_LOSS(DIODE)
Output diode junction temperature should be
maintained below 110ºC, but may vary depending
on application and/or system guidelines. The
diode θ_JA can be minimized with additional PCB
area on the cathode. PCB heatsinking the anode
may degrade EMI performance.
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.
AAT1230
18V 100mA Step-Up Converter
Selecting the Boost Inductor
The AAT1230 controller utilizes hysteretic control
and the switching frequency varies with output load
and input voltage. The value of the inductor deter-
mines the maximum switching frequency of the
AAT1230 boost converter. Increased output induc-
tance decreases the switching frequency, resulting
in higher peak currents and increased output volt-
age ripple. To maintain 2MHz maximum switching
frequency and stable operation, an output inductor
sized from 1.5µH to 2.7µH is recommended.
A better estimate of D_MAX is possible when V_F is
known.
D_MAX
=
(V_OUT + V_F -
(V_OUT +
V_IN(MIN))
V_F)
Where V_F 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.
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.
2.0
1.8
VIN = 3.0V
VOUT = 18V
VIN = 3.0V
VOUT = 15V
1.6
VIN = 3.6V
VIN = 3.6V
VOUT = 18V VOUT = 15V
1.4
1.2
1.0
0.8
0.6 V_IN = 2.7V V_IN = 2.7V
0.4 ^{VOUT = 18V VOUT = 15V}
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Output Current (mA)
1230.2006.03.1.0
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