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LM2596SX-5.0/NOPB 参数 Datasheet PDF下载

LM2596SX-5.0/NOPB图片预览
型号: LM2596SX-5.0/NOPB
PDF下载: 下载PDF文件 查看货源
内容描述: LM2596 SIMPLE SWITCHER电源转换器150千赫3A降压型稳压器 [LM2596 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator]
分类和应用: 转换器稳压器
文件页数/大小: 42 页 / 4730 K
品牌: TI [ TEXAS INSTRUMENTS ]
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LM2596  
SNVS124C NOVEMBER 1999REVISED APRIL 2013  
www.ti.com  
DISCONTINUOUS MODE OPERATION  
The selection guide chooses inductor values suitable for continuous mode operation, but for low current  
applications and/or high input voltages, a discontinuous mode design may be a better choice. It would use an  
inductor that would be physically smaller, and would need only one half to one third the inductance value needed  
for a continuous mode design. The peak switch and inductor currents will be higher in a discontinuous design,  
but at these low load currents (1A and below), the maximum switch current will still be less than the switch  
current limit.  
Discontinuous operation can have voltage waveforms that are considerable different than a continuous design.  
The output pin (switch) waveform can have some damped sinusoidal ringing present. (See Typical Performance  
Characteristics photo titled Discontinuous Mode Switching Waveforms) This ringing is normal for discontinuous  
operation, and is not caused by feedback loop instabilities. In discontinuous operation, there is a period of time  
where neither the switch or the diode are conducting, and the inductor current has dropped to zero. During this  
time, a small amount of energy can circulate between the inductor and the switch/diode parasitic capacitance  
causing this characteristic ringing. Normally this ringing is not a problem, unless the amplitude becomes great  
enough to exceed the input voltage, and even then, there is very little energy present to cause damage.  
Different inductor types and/or core materials produce different amounts of this characteristic ringing. Ferrite core  
inductors have very little core loss and therefore produce the most ringing. The higher core loss of powdered iron  
inductors produce less ringing. If desired, a series RC could be placed in parallel with the inductor to dampen the  
ringing. The computer aided design software Switchers Made Simple (version 4.3) will provide all component  
values for continuous and discontinuous modes of operation.  
Figure 29. Post Ripple Filter Waveform  
OUTPUT VOLTAGE RIPPLE AND TRANSIENTS  
The output voltage of a switching power supply operating in the continuous mode will contain a sawtooth ripple  
voltage at the switcher frequency, and may also contain short voltage spikes at the peaks of the sawtooth  
waveform.  
The output ripple voltage is a function of the inductor sawtooth ripple current and the ESR of the output  
capacitor. A typical output ripple voltage can range from approximately 0.5% to 3% of the output voltage. To  
obtain low ripple voltage, the ESR of the output capacitor must be low, however, caution must be exercised when  
using extremely low ESR capacitors because they can affect the loop stability, resulting in oscillation problems. If  
very low output ripple voltage is needed (less than 20 mV), a post ripple filter is recommended. (See Figure 20.)  
The inductance required is typically between 1 μH and 5 μH, with low DC resistance, to maintain good load  
regulation. A low ESR output filter capacitor is also required to assure good dynamic load response and ripple  
reduction. The ESR of this capacitor may be as low as desired, because it is out of the regulator feedback loop.  
The photo shown in Figure 29 shows a typical output ripple voltage, with and without a post ripple filter.  
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