©

§

2 x L

©

§

x

x

1

f

©

§

1+

©

§

C1

10 µF

2.2 µH

L1

SW

FB

LP3923

C2

LP3923

SNVS567B – APRIL 2010 – REVISED MAY 2013

www.ti.com

Buck Converter Application Information

BUCK OUTPUT VOLTAGE SELECTION

Buck output voltage can be programmed via the selection of the external feedback resistor network forming the

output feedback between the output voltage side of the inductor and the FB pin and the FB pin and GND.

Figure 5. Buck Converter Components

around 200 k

Ω to keep the current drawn through the resistor network to a minimum but large enough that it is

not susceptible to noise. If R2 is 200 k

will be 2.5 µA.

The formula for output voltage selection is

(2)

- feedback voltage (0.5V)

The recommended value for C1 is 2.2 pF to 5.1 pF, and for C2 is 15 pF.

Table 15. Component Configurations for Various Output Voltage Values

C1 [pF]

C2 [pF]

L [µH]

1.4

360

200

2.2 to 5.1

15

2.2

10

1.6

390

178

2.2 to 5.1

15

2.2

10

1.8

390

150

2.2 to 5.1

15

2.2

10

2.0

453

150

2.2 to 5.1

15

2.2

10

INDUCTOR SELECTION

There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor

current ripple is small enough to achieve the desired output voltage ripple. Different saturation current rating

specs are followed by different manufacturers so attention must be given to details. Saturation current ratings are

typically given at 25°C so ratings at the application maximum ambient temperature should be requested from the

manufacturer.

There are two methods to choose the inductor saturation current rating.

Method 1

The total current is the sum of the load and the inductor ripple current. This can be written as:

(3)

22

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