STEP-DOWN, SYNCHRONOUS PWM CONTROL SWITCHING REGULATOR CONTROLLER

S-8533 Series

12



External Parts Selection

1. Inductor

η).

driveability of the switching transistor is insufficient.

reaches the maximum at a certain L value. As the L value is made even larger, the efficiency degrades since the

An inductance of 22

μH is recommended for the S-8533 Series.

When choosing an inductor, attention to its allowable current should be paid since the current exceeding the

allowable value will cause magnetic saturation in the inductor, leading to a marked decline in efficiency and the

breakdown of the IC due to large current.

following equation :

IN

OSC

OUT

IN

OUT

OUT

PK

V

L

f

2

)

V

(V

V

I

I

×

×

×

−

×

+

=

supplied, and select a capacitor that has low ESR (Equivalent Series Resistance) and large capacitance. It should

be approximately 47 to 100

μF, although the actual value depends on the impedance of the power source used and

load current value. When the input voltage is low and the load is large, the output voltage may become unstable.

In this case, increase the input capacitance.

smoothen the ripple voltage. When the input voltage is extremely high or the load current is extremely large, the

output voltage may become unstable. In this case, the unstable area will become narrow by selecting a large

capacitance for an output side capacitor. A tantalum electrolytic capacitor is recommended since the unstable area

widens when a capacitor with a large ESR, such as an aluminum electrolytic capacitor, or a capacitor with a small

ESR, such as a ceramic capacitor, is chosen. The range of the capacitance should generally be approximately 47

to 100

μF.

Fully evaluate input and output capacitors under the actual operating conditions to determine the best value.