LM2671

SNVS008K – SEPTEMBER 1998 – REVISED APRIL 2013

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ON/OFF

This input provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any

voltage less than 0.8V will completely turn OFF the regulator. The current drain from the input supply when OFF

is only 50

μA. The ON/OFF input has an internal pull-up current source of approximately 20μA and a protection

clamp zener diode of 7V to ground. When electrically driving the ON/OFF pin the high voltage level for the ON

condition should not exceed the 6V absolute maximum limit. When ON/OFF control is not required this pin

should be left open.

DAP (WSON PACKAGE)

The Die Attach Pad (DAP) can and should be connected to the PCB Ground plane/island. For CAD and

assembly guidelines refer to Application Note SNOA401.

LM2671 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

To simplify the buck regulator design procedure, Texas Instruments

is making available computer design software to be used with the

SIMPLE SWITCHER line of switching regulators.LM267X Made

operating systems.

Given:

Given:

1. Inductor Selection (L1)

1. Inductor Selection (L1)

A. Select the correct inductor value selection guide from Figure 24

A. Use the inductor selection guide for the 5V version shown in

and Figure 25 or Figure 26 (output voltages of 3.3V, 5V, or 12V

Figure 25.

respectively). For all other voltages, see the design procedure for the

adjustable version.

B. From the inductor value selection guide, identify the inductance

B. From the inductor value selection guide shown in Figure 25, the

region intersected by the Maximum Input Voltage line and the

inductance region intersected by the 12V horizontal line and the 500

Maximum Load Current line. Each region is identified by an

mA vertical line is 47

μH, and the inductor code is L13.

inductance value and an inductor code (LXX).

C. Select an appropriate inductor from the four manufacturer's part

C. The inductance value required is 47

μH. From the table in

numbers listed in Table 1. Each manufacturer makes a different style Table 1, go to the L13 line and choose an inductor part number from

of inductor to allow flexibility in meeting various design requirements. any of the four manufacturers shown. (In most instances, both

Listed below are some of the differentiating characteristics of each

through hole and surface mount inductors are available.)

manufacturer's inductors:

Schott: ferrite EP core inductors; these have very low leakage

magnetic fields to reduce electro-magnetic interference (EMI) and

are the lowest power loss inductors

Renco: ferrite stick core inductors; benefits are typically lowest cost

inductors and can withstand E•T and transient peak currents above

rated value. Be aware that these inductors have an external

magnetic field which may generate more EMI than other types of

inductors.

Pulse: powered iron toroid core inductors; these can also be low cost

and can withstand larger than normal E•T and transient peak

currents. Toroid inductors have low EMI.

Coilcraft: ferrite drum core inductors; these are the smallest physical

size inductors, available only as SMT components. Be aware that

these inductors also generate EMI—but less than stick inductors.

Complete specifications for these inductors are available from the

respective manufacturers. A table listing the manufacturers' phone

numbers is located in Table 2.

A. Select an output capacitor from the output capacitor table in

A. Use the 5.0V section in the output capacitor table in Table 10.

Table 10. Using the output voltage and the inductance value found in Choose a capacitor value and voltage rating from the line that

the inductor selection guide, step 1, locate the appropriate capacitor

contains the inductance value of 47

μH. The capacitance and

value and voltage rating.

voltage rating values corresponding to the 47

μH inductor are the:

12

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