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参数资料
| 型号： | LMX2575MX-5.0 |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 3.2 A SWITCHING REGULATOR, 63 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封装： | SMT-24 |
| 文件页数： | 13/30页 |
| 文件大小： | 676K |
| 代理商： | LMX2575MX-5.0 |
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Additional Applications (Continued)
Definition of Terms
BUCK REGULATOR
A switching regulator topology in which a higher voltage is
converted to a lower voltage. Also known as a step-down
switching regulator.
BUCK-BOOST REGULATOR
A switching regulator topology in which a positive voltage is
converted to a negative voltage without a transformer.
DUTY CYCLE (D)
Ratio of the output switch’s on-time to the oscillator period.
CATCH DIODE OR CURRENT STEERING DIODE
The diode which provides a return path for the load current
when the LM2575 switch is OFF.
EFFICIENCY (
η)
The proportion of input power actually delivered to the load.
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 ca-
pacitor heating, which directly affects the capacitor’s operat-
ing lifetime. When used as a switching regulator output filter,
higher ESR values result in higher output ripple voltages.
Most standard aluminum electrolytic capacitors in the
100
F–1000
F
range
have
0.5
to 0.1 ESR.
Higher-grade capacitors (“low-ESR”, “high-frequency”, or
“low-inductance”’) in the 100 F–1000 F range generally
have ESR of less than 0.15
.
EQUIVALENT SERIES INDUCTANCE (ESL)
The pure inductance component of a capacitor (see
Figure
16). The amount of inductance is determined to a large ex-
tent 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 de-
termined 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 LM2575 when in the standby
mode (ON /OFF pin is driven to TTL-high voltage, thus turn-
ing 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.
DS011475-20
Note: Pin numbers are for the TO-220 package.
FIGURE 15. 1.2V to 55V Adjustable 1A Power Supply with Low Output Ripple
DS011475-21
FIGURE 16. Simple Model of a Real Capacitor
www.national.com
20
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