Page 10

January 1999 TOKO, Inc.

TK11830

APPLICATION INFORMATION

COMPONENT REQUIREMENTS

Inductor

DC resistance of the inductor must be less than 5

Ω. For

optimal performance and efficiency, an inductor with a DC

resistance of less than 1

Ω is recommended. The oscillator

frequency is inversely proportional to inductance. The

inductance should be greater than 300

µH to prevent loss

of efficiency at high frequencies.

There is a large peak current (up to I

the inductor is saturated.

C

The filtered output ripple is fed back to the feedback pin. To

ensure continuous operation, C

between the feedback pin and ground. If a large voltage is

fed back to the feedback pin, the power transistor switch

drive will be intermittent. This causes a large ripple voltage

since I

by the value of the output capacitor, C

resistance, R

when the ripple voltage is high due to the lower C

is used to prevent oscillation of the band gap reference and

to stabilize the feedback loop. The input capacitor, C

used to reduce supply impedance and to provide sufficient

input current during switching for stable circuit operation.

Recommended values:

C

C

C

C

Note: C

ESR to minimize ripple voltage.

Control Pin Resistor (R

Input requirements of the Control pin are as follows:

When V

stopped. When V

resumed.

A control current of 3

µA (typ.) is required for shutdown.

Shutdown voltage, V

R

changed.

V

V

R

ICONT

+

VCONT

RCONT

VBE

30 k

ON/OFF CONTROL

-4

-2

-5

-3

-1

VCONT

0

TA = 25 °C

0

1

2

4

2

5

3

1

0

ILPK

IL

t

L(SMALL)

L(LARGE)

t

ILPK(MAX)

-300 mA

INDUCTOR

SATURATION