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LM2576T-5.0 Datasheet(PDF) 20 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor. Click here to check the latest version.
Part No. LM2576T-5.0
Description  SIMPLE SWITCHER 3A Step-Down Voltage Regulator
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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 20 page
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Definition of Terms (Continued)
CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR)
The purely resistive component of a real capacitor’s imped-
ance (see Figure 16). It causes power loss resulting in
capacitor heating, which directly affects the capacitor’s op-
erating lifetime. When used as a switching regulator output
filter, higher ESR values result in higher output ripple volt-
ages.
Most standard aluminum electrolytic capacitors in the
100 µF–1000 µF range have 0.5
Ω to 0.1Ω ESR. Higher-
grade capacitors (“low-ESR”, “high-frequency”, or “low-
inductance”) in the 100 µF–1000 µF range generally have
ESR of less than 0.15
Ω.
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 volt-
age. 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 deter-
mined 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 speci-
fied temperature.
STANDBY QUIESCENT CURRENT (I
STBY)
Supply current required by the LM2576 when in the standby
mode (ON /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 operat-
ing 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 induc-
tor appears less inductive and the resistive component domi-
nates. Inductor current is then limited only by the DC resis-
tance of the wire and the available source current.
OPERATING VOLT MICROSECOND CONSTANT (E
T
op)
The product (in VoIt
µs) of the voltage applied to the inductor
and the time the voltage is applied. This E
T
op 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
01147625
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
01147622
LM2576T-XX Flow LB03
or LM2576HVT-XX Flow LB03
NS Package Number T05D
Note 15: (XX indicates output voltage option. See ordering information table
for complete part number.)
01147620
FIGURE 16. Simple Model of a Real Capacitor
www.national.com
20




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