AN734 Datasheet, PDF (1/5 Pages) Vishay Siliconix – Design Guidelines for the Low-Noise Low-Dropout Regulator Si9181

AN734
Vishay Siliconix
Design Guidelines for the Low-Noise
Low-Dropout Regulator—Si9181
Nitin Kalje
INTRODUCTION
This application note discusses the operation and features of
the Si9181, a 350-mA CMOS low-dropout (LDO), low-noise
voltage regulator. Providing very low ground current to extend
battery life, the Si9181 also offers superior line/load transient
response and ripple rejection. Designed to maintain regulation
while delivering currents from 0 mA to 600 mA, the Si9181
regulator also features an “out of regulation” error flag signal
and ON/OFF control input for complete shutdown.
The Si9181 was designed for applications requiring a regu-
lated voltage equal to or less than the voltage of the source or
battery, and requiring very low output noise. Such applications
include digital signal processors, baseband circuits, mixers, A-
to-D converters, or intermediate amplifiers. The Si9181’s LDO
characteristics are determined by its voltage, ground current,
power-dissipation, peak current capability, noise and ripple re-
jection specifications. The Si9181 is designed to meet the cri-
teria for high quality on each of these determinants, and is
suitable for portable and noise–sensitive appliances such as
cellular phones.
C_NOISE
4
V_IN
C_IN
2.2 mF
8
SD
ON
OFF
3
GND
6 ADJ
1
C_NOISE
S19181
U1
+
–
To V_IN
6 MW
60 mV
5% V_{REF +}
2.2 mA
Q1
+
–
U2
+
1.215 V
V_{REF –}
U3
–
+
R₂
V_ADJ
R₁
5
C_OUT
2.2 mF
2
C_DELAY
0.1 mF
Q2
7
V_OUT
R_EXT
ERROR
FIGURE 1. 350-mA CMOS LDO Regulator (Adjustable Output)
Document Number: 71337
31-Oct-00
www.vishay.com
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