AN2620 datasheet(14/20 Pages) STMICROELECTRONICS

14 / 20 page

Board usage recommendation

AN2620

14/20

Doc ID 13883 Rev 3

Figure 9.

ST1S10 application schematic for heavy capacitive load

4.5

Low output voltage (Vout < 2.5 V) and 2.5 V < Vin < 8 V

For applications with lower output voltage levels (Vout < 2.5 V) the output capacitance and

the inductor values should be selected in a way that improves the DC-DC control loop

behavior.

In this output condition two cases must be considered: Vin > 8 V and Vin < 8 V.

For Vin < 8 V the use of 2 x 22 µF capacitors in parallel to the output is recommended, as

shown in Figure 10.

For Vin > 8 V, a 100 µF electrolytic capacitor with ESR < 0.1 should be added in parallel to

the 2 x 22 µF output capacitors as shown in Figure 11.

Figure 10.

ST1S10 application schematic for low output voltage (Vout < 2.5 V) and

2.5 V < Vin < 8 V

4-8

OUT

SYNC

GND

2-3 = INH-OFF

1-2 = INH-ON

IC1

ePad*

R1 = 100 k

R2 = 20 k

R3 = 10 k

C1 = 4.7

µF

C2 = 22

µF

C3 = 0.1~4.7

µF

L1 = 3.3

µH

IC1 = ST1S10

*ePad Connected to GND

GND

OUT

12 V

5 V

OUT

C4 = 4.7 nF

4-8

OUT

SYNC

GND

2-3 = INH-OFF

1-2 = INH-ON

IC1

ePad*

R1 = 100 k

R2 = 20 k

R3 = 10 k

C1 = 4.7

µF

C2 = 22

µF

C3 = 0.1~4.7

µF

L1 = 3.3

µH

IC1 = ST1S10

*ePad Connected to GND

GND

OUT

12 V

5 V

OUT

C4 = 4.7 nF

25 4-8

Vout

SYNC

Vin

GND

2-3=INH-OFF

1-2=INH-ON

IC1

ePad*

R1=*

R2=2 k Ω

R3=10 k Ω

C1=2*4.7 µF or 10 µF

C2=2*22 µF

C3=0.47~1 µF

GND

Vout

<2.5Vout

8<Vin

L1=2.2 µH to 1 µH

IC1=ST1S10

*ePad Connected to GND

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