LM2672 datasheet(17/25 Pages) NSC

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LM2672 Series Buck Regulator

Design Procedure (Adjustable

Output)

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

To simplify the buck regulator design procedure, National

Semiconductor is making available computer design software to

be used with the SIMPLE SWITCHER line of switching

regulators. LM267X Made Simple version 6.0 is available on

Windows

3.1, NT, or 95 operating systems.

Given:

OUT = Regulated Output Voltage

OUT = 20V

IN(max) = Maximum Input Voltage

IN(max) = 28V

LOAD(max) = Maximum Load Current

LOAD(max) = 1A

F = Switching Frequency

(Fixed at a nominal 260 kHz).

F = Switching Frequency

(Fixed at a nominal 260 kHz).

1. Programming Output Voltage (Selecting R

1 and R2,as

shown in

Figure 3)

Use the following formula to select the appropriate resistor

values.

1. Programming Output Voltage (Selecting R

1 and R2,as

shown in

Figure 3)

Select R

1 to be 1 kΩ, 1%. Solve for R2.

where V

REF = 1.21V

Select a value for R

1 between 240Ω and 1.5 kΩ. The lower

resistor values minimize noise pickup in the sensitive feedback

pin. (For the lowest temperature coefficient and the best stability

with time, use 1% metal film resistors.)

2 =1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ.

2 = 15.4 kΩ.

AVX TPS

Recommended

Application Voltage

Voltage

Rating

+85˚C Rating

3.3

6.3

510

Sprague 594D

Recommended

Application Voltage

Voltage

Rating

+85˚C Rating

2.5

3.3

6.3

510

816

FIGURE 15. Recommended Application Voltage for AVX TPS and

Sprague 594D Tantalum Chip Capacitors Derated for 85˚C.

LM2672 Datasheet(PDF) 17 Page - National Semiconductor (TI)

LM2672 Datasheet(HTML) 17 Page - National Semiconductor (TI)

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