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APPLICATION INFORMATION

ADJUSTABLE OUTPUT VOLTAGE VERSION

V

O +

0.5 V

1 )

R1

R2

(3)

C1 +

1

2

p

10 kHz

R1

(4)

C2 +

R1

R2

C1

(5)

VIN

VIN

EN

MODE

SW

FB

PGND

PGND

SW

GND

2

3

1

4

9

10

5

7

8

6

TPS62020

C3

22

µF

2.5 V to 6 V

L1

6.2

µH

C4

22

µF

1.8 V / 600 mA

R1

470 k

Ω

R2

180 k

Ω

C1

33 pF

C2

100 pF

TPS62020, TPS62021

SLVS076B – JUNE 2003 – REVISED APRIL 2004

When the adjustable output voltage version TPS62020 is used, the output voltage is set by the external resistor

divider. See Figure 15.

The output voltage is calculated as:

with R1 + R2

≤ 1 MΩ and internal reference voltage V

R1 + R2 should not be greater than 1 M

Ω because of stability reasons. To keep the operating quiescent current

to a minimum, the feedback resistor divider should have high impedance with R1+R2

≤1 MΩ. Due to this and the

capacitive divider C1 and C2 across the feedback resistors minimizes the noise at the feedback, without

degrading the line or load transient performance.

C1 and C2 should be selected as:

with:

• R1 = upper resistor of voltage divider

• C1 = upper capacitor of voltage divider

For C1 a value should be chosen that comes closest to the calculated result.

with:

• R2 = lower resistor of voltage divider

• C2 = lower capacitor of voltage divider

For C2, the selected capacitor value should always be selected larger than the calculated result. For example, in

Figure 15 for C2 100 pF are selected for a calculated result of C2 = 88.42 pF.

If quiescent current is not a key design parameter C1 and C2 can be omitted, and a low impedance feedback

divider has to be used with R1 + R2 < 100 k

Ω. This reduces the noise available on the feedback pin (FB) as well

but increases the overall quiescent current during operation. The higher the programmed output voltage the

lower the feedback impedance has to be for best operation when not using C1 and C2.

Figure 15. Adjustable Output Voltage Version

12