13

LT1534/LT1534-1

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

Lf V

PEAK

OUT

OUT

IN

IN

OUT

IN

OUT

=+

()

















–

•• •

2

L = inductance value

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

SHDN

SYNC

COL

NFB

LT1534-1

GND

2.7V TO 10V

15

2

12

4

5

6

11

2700pF

16.9k

NOTE 1: 25nH TRACE INDUCTANCE

OR COILCRAFT B10T

L1, L2: COILTRONICS CTX50-4

NOTE 1

10

µF

0.047

µF

MBR330

MBR330

2.49k

1%

10k

2.49k

1%

10

1,8,

9,16

21.5k

1%

9.31k

1%

C1

47

µF

P6KE-20A

1N4148

C2

47

µF

– 12V

50mA

12V

50mA

1534 TA04

PGND

FB

3

14

13

7

10

Ω

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 = 100

µH

47

µF

L1

50

µH

47

µF

+

+

L2

50

µH

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