TPS62040

TPS62042,TPS62043

TPS62044,TPS62046

SLVS463A − JUNE 2003 − REVISED OCTOBER 2003

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13

APPLICATION INFORMATION

ADJUSTABLE OUTPUT VOLTAGE VERSION

When the adjustable output voltage version TPS62040 is used, the output voltage is set by the external resistor

divider. See Figure 15.

The output voltage is calculated as:

V

O +

0.5 V

1

) R1

R2

with R1 + R2

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 low

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:

C1

+

1

2

p

10 kHz

R1

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.

C2

+ R1

R2

C1

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 kΩ. 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.

VIN

VIN

EN

MODE

SW

FB

PGND

PGND

SW

GND

2

3

1

49

10

5

7

8

6

TPS62040

C3

10

µF

VI

2.5 V to 6 V

L1

10

µH

C4

10

µF

VO

1.8 V / 1.2 A

R1

470 k

Ω

R2

180 k

Ω

C1

33 pF

C2

100 pF

Figure 15. Adjustable Output Voltage Version

(3)

(4)

(5)