13
LT1534/LT1534-1
APPLICATIONS INFORMATION
WUU
U
2. Calculate peak inductor current at full load current to
ensure that the inductor will not saturate. Peak current
can be significantly higher than output current, espe-
cially with smaller inductors and lighter loads, so don’t
omit this step. Powdered iron cores are forgiving be-
cause they saturate softly, whereas ferrite cores satu-
rate abruptly. Other core material falls in between. The
following formula assumes continuous mode opera-
tion but it errors only slightly on the high side for dis-
continuous mode, so it can be used for all conditions.
II
V
V
VV V
LfV
PEAK OUT
OUT
IN
IN OUT IN
OUT
=+
()
–
•••2
L = inductance value
V
IN
= supply voltage
V
OUT
= output voltage
I = output current
f = oscillator frequency
3. Choose a core geometry. For low EMI problems a
closed structure should be used such as a pot core, ER
core, E core or toroid (see AN70 appendix I).
4. Select an inductor that can handle peak current, aver-
age current (heating effects) and fault current.
5. Finally, double check output voltage ripple. The experts
in the Linear Technology Applications department have
experience with a wide range of inductor types and can
assist you in making a good choice.
Further Help
AN70 has more information on noise in switching regula-
tors and its measurement. AN19 has general information
on switcher design. The Linear Technology applications
group is always ready to lend a helping hand.
TYPICAL APPLICATIO S
U
SHDN
SYNC
COL
NFB
LT1534-1
GND
V
IN
2.7V TO 10V
15
212
4
5
6
11
2700pF
16.9k
NOTE 1: 25nH TRACE INDUCTANCE
OR COILCRAFT B10T
L1, L2: COILTRONICS CTX50-4
NOTE 1
10µF
0.047µF
MBR330
MBR330
2.49k
1%
10k
2.49k
1%
101,8,
9,16
21.5k
1%
9.31k
1%
C1
47µF
P6KE-20A
1N4148
C2
47µF
–12V
50mA
12V
50mA
1534 TA04
C
T
R
T
V
C
PGND
R
VSL
R
CSL
FB
3
14
13
7
10Ω
1nF
+
+
9
3
8
4
T1
2
10
17
PIN 1 TO TO 10, 16 TURNS 24AWG
PIN 3 TO 8, 45 TURNS 38AWG
PIN 4 TO 7, 45 TURNS 36AWG
PIN 2 TO 9, 16 TURNS 24AWG
T1: PHILIPS EFD-15-3F3 CORE
GAP FOR PRIMARY
L = 100µH
47µF
L1
50µH
47µF
+
+
L2
50µH
OPTIONAL
Low Noise ±12V Dual Output Flyback Converter with Dual Polarity Output Voltage Sensing
