10

LT1373

maximum output load current and will also be increased if

poor quality (high ESR) output capacitors are used. The

addition of a 0.001

switching frequency ripple to only a few millivolts. A low

margin may be inadequate.

Switch Node Considerations

For maximum efficiency, switch rise and fall time are made

as short as possible. To prevent radiation and high fre-

quency resonance problems, proper layout of the compo-

nents connected to the switch node is essential. B field

(magnetic) radiation is minimized by keeping output di-

ode, switch pin and output bypass capacitor leads as short

as possible. E field radiation is kept low by minimizing the

length and area of all traces connected to the switch pin.

A ground plane should always be used under the switcher

circuitry to prevent interplane coupling.

Positive-to-Negative Converter with Direct Feedback

LT1373

2.7V TO 16V

1

3

8

5

4

6, 7

*COILTRONICS CTX20-2 (407) 241-7876

GND

NFB

LT1373 • TA03

S/S

D2

P6KE-15A

D3

1N4148

D1

MBRS130LT3

C1

22

µF

C2

0.01

µF

R1

5k

R3

2.49k

1%

R2

2.55k

1%

†

–5V

C3

47

µF

ON

OFF

3V

5V

9V

0.3A

0.5A

0.75A

2

1

4

T1*

3

•

•

+

+

Dual Output Flyback Converter with Overvoltage Protection

LT1373

FB

4.75V TO 13V

1

3

8

5

2

4

6, 7

*DALE LPE-4841-100MB (605) 665-9301

GND

NFB

LT1373 • TA04

S/S

P6KE-20A

1N4148

MBRS140T3

MBRS140T3

C1

100

µF

R2

275k

1%

R1

302.6k

1%

C2

0.01

µF

R3

5k

R5

2.49k

1%

R4

12.4k

1%

–15V

15V

C3

47

µF

C4

47

µF

ON

OFF

2, 3

6, 7

5

T1*

4

8

1

•

•

•

+

+

+

The high speed switching current path is shown schemati-

cally in Figure 3. Minimum lead length in this path is

essential to ensure clean switching and low EMI. The path

including the switch, output diode and output capacitor is

the only one containing nanosecond rise and fall times.

Keep this path as short as possible.

More Help

For more detailed information on switching regulator

circuits, please see AN19. Linear Technology also offers a

computer software program, SwitcherCAD

designing switching converters. In addition, our applica-

tions department is always ready to lend a helping hand.

LOAD

L1

SWITCH

NODE

LT1373 • F03

HIGH

FREQUENCY

CIRCULATING

PATH

Figure 3

APPLICATIO S I FOR ATIO

SwitcherCAD is a trademark of Linear Technology Corporation.