DC/DC Step-Down Converter IC

SI-8000TM Series

September 2005

Sanken Electric Co.,Ltd.

I02-001EA-050910

6-1 Standard circuit diagram

VIN

1

GND

GN

D

2

4

5

3

GND

SS

IN

SW

ADJ

C1

220uF

C2

470uF

L 47uH

Di

SI-8008TM

R1

R2

C3

Diode Ｄｉ

・

The shottky-barrier diode must be used for Di. If other diodes like fast recovery diodes are used, IC

may be destroyed because of the reverse voltage applied by the recovery voltage or ON voltage.

Choke coil Ｌ1

・

If the winding resistance of the choke coil is too high, the efficiency may go down to the extent that

it is out of the rating.

・

As the overcurrent protection start current is approx. 2.5A, attention must be paid to the heating of

the choke coil by the magnetic saturation due to overload or short-circulated load.

Capacitor Ｃ1，Ｃ2，Ｃ3

・

As large ripple currents flow across C1 and C2, capacitors with high frequency and low impedance

for SMPS must be used. Especially when the impedance of C2 is high, the switching waveform may

not be normal at low temperature. Please use neither OS capacitor nor tantalum capacitor which

causes an abnormal oscillation for the C2.

・

C3 is a capacitor for soft start. In case soft start function is not used, please keep No.5 terminal open.

A pull-up resistor is provided inside the IC.

Resister R1，R2

・

by the following expression.

◎

In order to have optimum operating condition, each component must be laid out with the minimum

distance.

C1：220μF

C2：470μF

C3：1μF

(If soft start function is used)

L1：47μH

Di：SFPB66

(Made by Sanken)

(

) ()()

()

Ω

×

=

=

Ω

×

−

=

−

=

−

−

k

I

V

R

V

I

V

V

R

ADJ

ADJ

OUT

ADJ

ADJ

OUT

8

.

0

10

1

8

.

0

2

10

1

8

.

0

1

3

3

≒

，

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