Better Approach Dealing with Ripple Noise been trend that cellula

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Better Approach Dealing with Ripple Noise been trend that cellula

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AN019
Better Approach Dealing with Ripple Noise
been trend that cellular phones, audio systems, cordless phones portable appliances have requirement noise power supplies. talking about interesting subject control input noise caused external disturbance reduce output noise provide power with lower noise logic
power line capacitors improve noise problem. Besides, most featured with ripple rejection function reduce noise. Such AIC1730, lower output noise high ripple rejection bypass polarity followings describe details about inductor effect power line ripple rejection function.
general, ripple noise power line will influenced fast charge/discharge capacitors external switch converter input polarity, respectively. power source originally from output converter. output influenced ringing current, which caused rising falling edges switch MOSFET, power line. serious problem generate noise false signals input polarity from power line. order avoid problem, employ some bypass capacitors input capacitor close possible input polarity LDO. high-speed environment, inductive effect power line input capacitor become very critical. output polarity high-speed switch generates high frequency noise power line. ringing makes input capacitor with high lead inductor open circuit. open circuit prevents power line, flowing with current, from ripple noise input polarity, high noises output polarity false signals logic maintain system stable state. Conclusively, adding bypass capacitors (MLCC) reducing inductor effect
July 2001
influence inductor effect over
Formula inductor effect power line
VOUT
VOUT
COUT
Figure
Inductor Effect Power Line
Most printed circuit boards designed maintain short distances from input polarity well from power ground. result, users reduce inductor effect power line lead inductor capacitor. addition, better reliable system low-impedance path when bypass capacitor considered. shown figure1, input capacitor charged prevent drop. Therefore, distance between input polarity crucial point. inductor will disturb power line when works normally. inductor
AN019
effect calculated below:
Where: length input polarity distance wires radius wire permeability medium between wires
Power line
COUT
Figure
Power Line Equals Inductor
shown figure LDO, semiconductor component, similar configuration capacitor because most semiconductor discharging
inductor directly proportional distance between input polarity other words, shorter distances between well VOUT GND, less inductor effect will
components
possess
charging
functions. inductor effect power line calculated below:
L(inductor
this location input capacitor crucial LDO?
These series capacitors COUT) calculated
Power line
VOUT COUT
COUT COUT CCOUT
Thus, ringing frequency shown
Figure Power Line Distance Between
COUT CCOUT
inverse
shown figure input polarity disturbed long distance from Printed circuit boards need designed with shortest distance from input polarity well from power ground.
Where,
ringing
frequency
proportional CIT. reducing capacitance will affect noise input polarity influence stability system.
AN019
ripple noise when switch mode power supply
Power line COUT
used power application. VOUT 10µF Electric Capacitor
Figure Different Location Input Capacitor VSIN Comparing figure with figure input capacitor located close possible input polarity, when length power line remains same. Thus calculated below: Figure
PSRR Circuit Measurement HP3577A
COUT COUT CCOUT CCOUT
Principle PSRR calculation defined
PSRR
ringing frequency shown
Based ripple rejection circuit, frequency from 300KHZ with amplitude 75mV, PSRR AIC1117-33 shown figure below.
LCIT
LCIN
result above, ringing will reduced distance from input capacitor (CIT) input polarity becomes shortest. noise, however inductor effect power line still existing unless users implement system with shortest length power line, required formula (1).
PSRR (ldBl)
AIC1117
Relocating input capacitor improve ripple
Ripple rejection capability
Frequency (KHz)
Measurement PSRR
Figure AIC1117 PSRR
Power supply rejection ratio (PSRR), also known ripple rejection, represents performance regulator, which prevents regulated output voltage disturbance caused input voltage variations. particular, PSRR filters output
AN019
Simple measurement PSRR
Function Generat Electric VOUT
AIC1117-33 PSRR 60KHZ calculated:
SCOPE
PSRR
5.8mV 28.5dB 155mV
Figure Simple Measurement Circuit PSRR
shown figure AIC1117-33 improves output ripple noise from 28.5dB 34.9dB when user employs 22µF electric capacitor, instead 10µF, input polarity.
waveform noise negative pole 10µF electric capacitor, which separate signal from signal figure bias 5V/DC, bearing 60KHZ signal, supplied input polarity LDO, example, AIC1117-33.
Avoiding abnormal oscillation itself
Properly selecting output capacitor
LDO, which features with output capacitor, does produce ripple noise itself, unless input polarity influenced external ripple noise. stability, output (high ESR) capacitor required between output ground. Without this capacitor, will oscillate temperature rising. Even though most capacitors work with LDO, equivalent series resistor (ESR) capacitors should held within capacitors aluminum recommended. figure Figure AIC1117-33 Ripple Rejection Test AIC1117-33 applied with load 200mA current. Please refer "guide operate AIC1730 ceramic" reasons oscillatory.
Figure
AIC1117-33 Ripple Rejection Test
AN019
Figure AIC1117-33 Abnormal Oscillation with Output 10µF Ceramic
Figure Abnormal Dynamic Impedance Figure AIC1117-33 Normal Output Voltage with Output 10µF Electric Loading 100mA
Properly selecting input capacitor
employment input capacitor necessary avoid abnormal oscillation because does have external compensation pin. important properly select input capacitor most LDOs. When input capacitor with loading current output polarity applied, zero point loop-gain plot will moving. movement zero point cause input polarity abnormally oscillated. Note that input oscillation influence output ripple noise. avoid noise caused oscillation, input capacitor absolute requirement LDO. large input capacitance definitely help stability system. Shown figure system unstable state input capacitor LDO. figure shows satisfactorily dynamic impedance when input capacitor employed. With input capacitor applied, abnormal oscillation occurs figure Figure Normal Dynamic Impedance Loading 100mA
Figure AIC1117-33 Abnormal Oscillation Input Polarity
AN019
length always been left consideration when applied system.
Again, would like point importance using shortest power line best performance reduce disturbance from switching converter. always essential minimize loop among VIN, ground, input capacitor, bypass capacitor.
Figure AIC1117-33
Abnormal
Oscillation
Ripple rejection represents capability filtering noise. Users must fully aware PSRR capability they need select proper ripple rejection capability LDO.
Output Polarity
Conclusion
Conclusively, major concern ripple noise power line length because power line influences system reliability indirectly through inductor effect. Either locating input capacitor close possible input polarity adding some bypass capacitors power line reduce complications completely eliminate ringing. concern power line
Therefore, suggesting users only concern about cost also performance when they making decision selecting LDO.
Ripple noise always been complicated problem some fields. crucial best resolution solve abnormality external disturbance. This obtained close attention layout trace PCB.
High output capacitor must applied LDO. Also employment input capacitor highly recommended input polarity. They result best most efficient performance dropout linear regulator.

Better Approach Dealing with Ripple Noise been trend that cellula

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