AAT1230 Datasheet, PDF (10/21 Pages) Advanced Analogic Technologies – 18V 100mA Step-Up Converter

AAT1230
18V 100mA Step-Up Converter
JP1
1
2
3
Enable
JP2
1
2
3
Select
R4 V_CC
10K
C1
2.2µF
U1 AAT1230
TSOPJW-12
1
2
3
4
5
6
VP
LIN
EN/SET FB1
SEL
FB2
VIN
GND
N/C
PGND
SW
SW
12
11
10
9
8
7
L1
2.2µH
R3
4.99k
D1
Schottky
R2
562
V_OUT
R1
78.7k
C2
2.2µF
25V
C1 10V 0805 2.2µF
C2 25V 0805 2.2µF
D1 30V 0.5A MBR0530T1 SOD-123
L1 2.2µH SD3814-2R2
R1 78.7k 0603
R2 562 0603
R3 4.99k 0603
Figure 1: AAT1230 Demo Board Schematic.
Application Information
Selecting the Output Diode
To ensure minimum forward voltage drop and no
recovery, high voltage Schottky diodes are consid-
ered the best choice for the AAT1230 boost convert-
er. The AAT1230 output diode is sized to maintain
acceptable efficiency and reasonable operating
junction temperature under full load operating condi-
tions. Forward voltage (V_F) and package thermal
resistance (θ_JA) are the dominant factors to consider
in selecting a diode. The diode's published current
rating may not reflect actual operating conditions
and should be used only as a comparative measure
between similarly rated devices. 20V rated Schottky
diodes are recommended for outputs less than 15V,
while 30V rated Schottky diodes are recommended
for outputs greater than 15V.
The switching period is divided between ON and
OFF time intervals.
tor to the output load through the output diode.
Duty cycle is defined as the ON time divided by the
total switching interval.
D=
T_ON
T_ON + T_OFF
= T_ON ⋅ F_S
The maximum duty cycle can be estimated from
the relationship for a continuous mode boost con-
verter. Maximum duty cycle (D_MAX) is the duty
cycle at minimum input voltage (V_IN(MIN)).
D_MAX =
V_OUT - V_IN(MIN)
V_OUT
The average diode current during the OFF time can
be estimated.
1
F_S
=
T_ON
+
T_OFF
During the ON time, the N-channel power MOS-
FET is conducting and storing energy in the boost
inductor. During the OFF time, the N-channel
power MOSFET is not conducting. Stored energy is
transferred from the input battery and boost induc-
I_AVG(OFF)
=
1
I_OUT
- D_MAX
The following curves show the V_F characteristics
for different Schottky diodes (100°C case). The V_F
of the Schottky diode can be estimated from the
average current during the off time.
10
1230.2006.03.1.0