AN025 Datasheet PDF - AIC
| Part Number | AN025 | |
| Description | Analysis of LDO oscillation issues | |
| Manufacturers | AIC | |
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There is a preview and AN025 download ( pdf file ) link at the bottom of this page. Total 6 Pages | ||
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Analysis of LDO oscillation issues
AN025
Introduction
Using low noise and stable power supplies is a trend for power application. And LDO is one
of the simplest applications. Yet LDO oscillation results in voltage instability. The analysis
below tells you how to prevent LDO from oscillation.
Vin Vout
Error
Amplifier
R1
+
Co
GND
Vref
LDO
R2
Fig 1.a: LDO basic structure
Vin
GND
S
Rds
VgsGp
Rpar Cpar
D
G
Error
Amplifier
Vref
LDO
Zo
Vout
R1 +
Co
Resr Cb
R2
Fig 1.b: LDO ac effective circuit
The LDO in fig. 1.a is composed of four parts - pass element, error amplifier, reference
voltage, and feedback resistor. The series pass element, PMOS transistor, is formed into a
small signal model. The parasitic parameters, Rpar and Cpar, are signified by the output
impedance of the error amplifier and the input impedance of PMOS. An ac prototype of LDO
1
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AN025
Effect of ESR of capacitor on LDO
Linear regulators require input and output capacitors to maintain stability. LDO does not
create ripple noise by itself, unless the input polarity is influenced by external ripple noise.
The output capacitor should be selected within the ESR range (shown as figure3 and 4).
Without an output capacitor (high ESR), LDO will oscillate as temperature increasing.
Solid tantalum electrolytic, aluminum electrolytic, and multiplayer ceramic capacitors are all
suitable, provided they meet the ESR requirements. But capacitors of aluminum and tantalum
electrolytic are recommended. Because the ceramic capacitor’s ESR is lower and its electrical
characteristics vary widely over temperature.
100
COUT=1µF
10
100
COUT=2.2µF
10
1 STABLE REGION
0.1
1
Stable Region
0.1
0.01
50
100
0.01
150
50 100 150
<Fig3>
I0(mA)
<Fig4>
I0(mA)
Fig3: Output Capacitor = 1µF
Fig4: Output Capacitor = 2.2µF
In figure5 and 6, AIC1730-33 is applied with 150mA load current. Figure5 shows unusual
oscillation with a 1uF ceramic output capacitor (ESR=100mΩ), and output voltage is normal
with a 1uF electric capacitor (ESR=500mΩ) which is shown as figure6.
5
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for AN025 electronic component. |
| Information | Total 6 Pages | |
| Link URL | [ Copy URL to Clipboard ] | |
| Download | [ AN025.PDF Datasheet ] | |
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