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APPLICATION INFORMATION

ADJUSTABLE OUTPUT VOLTAGE

V

O +

1.5

V

ref

1 )

R1

R2

with an internal reference voltage V

ref

typical + 0.4 V

(2)

AVIN

VIN

SW

TPS62300

L1

ADJ

C1

PGND

C2

VI

AGND

VOUT

R1

R2

EN

MODE/SYNC

A

A

FB

A

1

2

3

8

7

10

6

4

5

9

VO

1.6 V/500 mA

2.7 V . . 6 V

4.7

F

m

4.7

F

m

OUTPUT FILTER DESIGN (INDUCTOR AND OUTPUT CAPACITOR)

ƒc +

1

2p

L

C

O

+

1

2p 1 mH

10 mF

+ 50.3 kHz

(3)

TPS62300, TPS62301, TPS62302

TPS62303, TPS62305, TPS62311

TPS62313, TPS62320, TPS62321

SLVS528B – JULY 2004 – REVISED JUNE 2005

When the adjustable output voltage versions, TPS62300 or TPS62320, are used, the output voltage is set by the

external resistor divider (see Figure 32).

The output voltage is calculated as:

To keep the operating quiescent current to a minimum, it is recommended that R2 be set in the range of 75 k

Ω to

130 k

Ω. Route the FB line away from noise sources, such as the inductor or the SW line.

Figure 32. Adjustable Output Voltage Version

The TPS6230x, TPS6231x, and TPS6232x series of step-down converters have internal loop compensation.

Therefore, the external L-C filter must be selected to work with the internal compensation.

The device has been designed to operate with inductance values between a minimum of 0.7

µH and maximum of

6.2

µH. The internal compensation is optimized to operate with an output filter of L = 1 µH and C

an output filter has its corner frequency at:

Operation with a higher corner frequency (e.g., L = 1

µH, C

the loop stability be checked in detail. Selecting a larger output capacitor value (e.g., 22

µF) is less critical

because the corner frequency moves to lower frequencies with fewer stability problems. The possible output filter

combinations are listed in Table 1.

Regardless of the inductance value, operation is recommended with 10-

µF output capacitor in applications with

high-load transients (e.g.,

≥ 1600 mA/µs).

Table 1. Output Filter Combinations

INDUCTANCE (L)

1

µH

≥ 4.7 µF (ceramic capacitor)

2.2

µH

≥ 2.2 µF (ceramic capacitor)

The inductor value also has an impact on the pulse skipping operation. The transition into power-save mode

begins when the valley inductor current goes below a level set internally. Lower inductor values result in higher

ripple current which occurs at lower load currents. This results in a dip in efficiency at light load operations.

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