LM2576 datasheet(20/23 Pages) ARTSCHIP

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LM2576/LM2576HV

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Definition of Terms (Continued)

CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)

The purely resistive component of a real capacitor’s impedance

( see Figure 16 ). It causes power loss resulting in capacitor

heating ,which directly affects the capacitor’s operating lifetime.

When used as a switching regulator output filter, higher ESR

values result in higher output ripple voltages.

FIGURE 16. Simple Model of a Real Capacitor

Most standard aluminum electrolytic capacitors in the 100μF

-1000 μ F range have 0.5 Ω to 0.1 Ω ESR. Higher-grade

capacitors (“low-ESR”, “high-frequency”, or “low-inductance”) in

the 100μF -1000μF range generally have ESR of less than

0.15Ω.

EQUIVALENT SERIES INDUCTANCE (ESL)

The pure inductance component of a capacitor ( see Figure 16 ).

The amount of inductance is determined to a large extent on the

capacitor’s construction. In a buck regulator, this unwanted

inductance causes voltage spikes to appear on the output.

OUTPUT RIPPLE VOLTAGE

The AC component of the switching regulator’s output voltage.

It is usually dominated by the output capacitor’s ESR multiplied

by the inductor’s ripple current (△I IND ). The peak-to-peak

value of this sawtooth ripple current can be determined by

reading the Inductor Ripple Current section of the Application

hints.

CAPACITOR RIPPLE CURRENT

RMS value of the maximum allowable alternating current at

which a capacitor can be operated continuously at a specified

temperature.

STANDBY QUIESCENT CURRENT (ISTBY)

Supply current required by the LM2576 when in the standby

mode (

/OFF pin is driven to TTL-high voltage, thus turning

the output switch OFF).

INDUCTOR RIPPLE CURRENT (△I IND)

The peak-to-peak value of the inductor current waveform,

typically a sawtooth waveform when the regulator is operating

in the continuous mode (vs. discontinuous mode).

CONTINUOUS/DISCONTINUOUS MODE OPERATION

Relates to the inductor current. In the continuous mode, the

inductor current is always flowing and never drops to zero, vs.

the discontinuous mode, where the inductor current drops to

zero for a period of time in the normal switching cycle.

INDUCTOR SATURATION

The condition which exists when an inductor cannot hold any

more magnetic flux. When an inductor saturates, the inductor

appears less inductive and the resistive component dominates.

Inductor current is then limited only by the DC resistance of the

wire and the available source current.

OPERATING VOLT MICROSECOND CONSTANT (E●

Top)

The product (in Volt●μs) of the voltage applied to the inductor

and the time the voltage is applied. This E●Top constant is a

measure of the energy handling capability of an inductor and is

dependent upon the type of core, the core area, the number of

turns, and the duty cycle.

Connection Diagrams (Note 15)

Straight Leads

5-Lead TO-220(T)

Top View

01147621

LM2576T-XX or LM2576HVT-XX

NS Package Number T05A

TO-263(S)

5-Lead Surface-Mount Package

Top View

LM2576S-XX or LM2576HVS-XX

NS Package Number TS5B

LM2576SX-XX or LM2576HVSX-XX

NS Package Number TS5B, Tape and Reel

Bent, Staggered Leads

5-Lead TO-220 (T)

Top View

Side View

LM2576T-XX Flow LB03

Or LM2576HVT-XX Flow LB03

NS Package Number T05D

Note15:(XX indicates output voltage option. See ordering

information table for complete part number.)

LM2576 Datasheet(PDF) 20 Page - ARTSCHIP ELECTRONICS CO.,LMITED.

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