AAT1230_07 Datasheet, PDF (10/21 Pages) Advanced Analogic Technologies – 18V 100mA Step-Up Converter

AAT1230/1230-1
18V 100mA Step-Up Converter
JP1
3
2
1
Enable
JP2
3
2
1
Select
R4 _VIN
10K
C1
2.2μF
U1
1 _VP
LIN ¹²
2 _{EN/SET FB1} 11
3 _SEL
FB2 ¹⁰
4 _VIN
GND ⁹
5 _{N/C PGND} 8
6 _SW
SW ⁷
L1
2.2μH
D1
Schottky
R2
562
R3
4.99k
VOUT
R1
78.7k
C2
2.2μF
U1 AAT1230/1230-1 TSOPJW12
C1 10V 0603 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
R4 10k 0603
Figure 1: AAT1230/1230-1 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 AAT1230/1230-1 boost
converter. The AAT1230/1230-1 output diode is
sized to maintain acceptable efficiency and reason-
able operating junction temperature under full load
operating conditions. 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 oper-
ating conditions and should be used only as a com-
parative 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.
transferred from the input battery and boost induc-
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
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
1230.2007.06.1.6