5V/3.3V or Adjustable, Low-Dropout,
Low I
Q
, 200mA Linear Regulators
MAX882/MAX883/MAX884
80
70
60
I
OUT
= 1mA
PSRR (dB)
PSRR (dB)
50
40
30
20
10
0
10
0
10
1
10
2
10
3
10
4
10
5
10
6
FREQUENCY (Hz)
MAX884
∆V
IN
= 1V
P-P
C
IN
= 0µF
C
OUT
= 2.2µF
40
30
C
20
10
I
OUT
= 100mA
0
10
1
10
2
10
3
10
4
10
5
10
6
FREQUENCY (Hz)
MAX883
∆V
IN
= 1V
P-P
C
IN
= 0µF
I
OUT
= 100mA
B
A
60
50
A: C
OUT
= 1µF
B: C
OUT
= 10µF
C: C
OUT
= 100µF
MAX882/4-8a
Figure 8a. Power-Supply Rejection Ratio vs. Ripple Frequency
for Light and Heavy Loads
Figure 8b. Power-Supply Rejection Ratio vs. Ripple Frequency
for Various Output Capacitances
MAX882/4-8b
The filter capacitor’s size depends primarily on the
desired power-up time and load-transient responses.
Load-transient response is improved by using larger
output capacitors.
The output capacitor’s equivalent series resistance
(ESR) will not affect stability as long as you observe the
minimum capacitance requirement. The type of capaci-
tor selected is not critical, but it must remain above the
minimum value over the full operating temperature
range.
Noise
The MAX882/MAX883/MAX884 exhibit up to 4mV
p-p
of
noise during normal operation. This is negligible in
most applications. When using the MAX882/MAX883/
MAX884 for applications that include analog-to-digital
converters (ADCs) with resolutions greater than 12 bits,
consider the ADC’s power-supply rejection specifica-
tions. Refer to the output noise plot in the
Typical
Operating Characteristics
section.
Input Bypass Capacitor
Normally, use 0.1µF to 10µF capacitors on the MAX882/
MAX883/MAX884 input. The best value depends pri-
marily on the power-up slew rate of V
IN
, and on load
and line transients. Larger input capacitor values pro-
vide better supply-noise rejection and line-transient
response, as well as improved performance, when the
supply has a high AC impedance. The type of input
bypass capacitor used is not critical.
PSRR and Operation from
Sources Other than Batteries
The MAX882/MAX883/MAX884 are designed to
achieve low dropout voltages and low quiescent cur-
rents in battery-powered systems. However, to gain
these benefits, the devices must trade away power-
supply noise rejection, as well as swift response to sup-
ply variations and load transients. For a 1mA load
current, power-supply rejection ranges from 60dB
down to 20dB at 2kHz. At higher frequencies, the cir-
cuit depends primarily on the characteristics of the out-
put capacitor, and the PSRR increases (Figure 8).
12
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