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LM2673

SNVS030O – APRIL 2000 – REVISED JUNE 2016

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Copyright © 2000–2016, Texas Instruments Incorporated

Feature Description (continued)

7.3.2 Input

The input voltage for the power supply is connected to pin 2. In addition to providing energy to the load the input

voltage also provides bias for the internal circuitry of the LM2673. For ensured performance the input voltage

must be in the range of 8 V to 40 V. For best performance of the power supply the input pin must always be

bypassed with an input capacitor located close to pin 2.

7.3.3 C Boost

A capacitor must be connected from pin 3 to the switch output, pin 1. This capacitor boosts the gate drive to the

high efficiency. The recommended value for C Boost is 0.01 µF.

7.3.4 Ground

This is the ground reference connection for all components in the power supply. In fast-switching, high-current

applications such as those implemented with the LM2673, TI recommends that a broad ground plane be used to

minimize signal coupling throughout the circuit.

7.3.5 Current Adjust

A key feature of the LM2673 is the ability to tailor the peak switch current limit to a level required by a particular

application. This alleviates the need to use external components that must be physically sized to accommodate

current levels (under shorted output conditions for example) that may be much higher than the normal circuit

operating current requirements.

7.3.6 Feedback

This is the input to a two-stage high gain amplifier, which drives the PWM controller. It is necessary to connect

pin 6 to the actual output of the power supply to set the DC output voltage. For the fixed output devices (3.3-V, 5-

V, and 12-V outputs), a direct wire connection to the output is all that is required as internal gain setting resistors

are provided inside the LM2673. For the adjustable output version two external resistors are required to set the

dc output voltage. For stable operation of the power supply it is important to prevent coupling of any inductor flux

to the feedback input.

7.4 Device Functional Modes

7.4.1 Soft-Start

A capacitor connected from pin 7 to ground allows for a slow turnon of the switching regulator. The capacitor sets

a time delay to gradually increase the duty cycle of the internal power switch. This can significantly reduce the

amount of surge current required from the input supply during an abrupt application of the input voltage. If soft

start is not required this pin must be left open circuited. See CSS Soft-Start Capacitor for further information

regarding soft-start capacitor values.