MIC5206 Micrel Semiconductor, MIC5206 Datasheet - Page 6

• Manufacturer Part Number: MIC5206
• Description: 150mA Low-Noise LDO Regulator
• Manufacturer: Micrel Semiconductor

MIC5206
Applications Information
Enable/Shutdown
Forcing EN (enable/shutdown) high (> 2V) enables the regu-
lator. EN is compatible with CMOS logic gates.
If the enable/shutdown feature is not required, connect EN
(enable) to IN (supply input). Refer to the text with Figures 1a
and 2.
Input Capacitor
A 1 F capacitor should be placed from IN to GND if there is
more than 10 inches of wire between the input and the ac filter
capacitor or if a battery is used as the input.
Reference Bypass Capacitor
BYP (reference bypass) is connected to the internal voltage
reference. A 470pF capacitor (C
GND quiets this reference, providing a significant reduction in
output noise. See Figure 2. C
margin; when using C
greater are generally required to maintain stability.
The start-up speed of the MIC5206 is inversely proportional
to the size of the reference bypass capacitor. Applications
requiring a slow ramp-up of output voltage should consider
larger values of C
consider omitting C
If output noise is not a major concern, omit C
BYP open.
Output Capacitor
An output capacitor is required between OUT and GND to
prevent oscillation. The minimum size of the output capacitor
is dependent upon whether a reference bypass capacitor is
used. 1.0 F minimum is recommended when C
used (see Figure 2). 2.2 F minimum is recommended when
C
regulator’s transient response. The output capacitor value
may be increased without limit.
The output capacitor should have an ESR (effective series
resistance) of about 5
above 1MHz. Most tantalum or aluminum electrolytic capaci-
tors are adequate; film types will work, but are more expen-
sive. Since many aluminum electrolytics have electrolytes
that freeze at about –30 C, solid tantalums are recom-
mended for operation below –25 C.
At lower values of output current, less output capacitance is
required for output stability. The capacitor can be reduced to
0.47 F for current below 10mA or 0.33 F for currents below
1mA.
No-Load Stability
The MIC5205 will remain stable and in regulation with no load
(other than the internal voltage divider) unlike many other
voltage regulators. This is especially important in CMOS
RAM keep-alive applications.
Error Flag Ouput
The error flag is an open-collector output and is active (low)
when an undervoltage of approximately 5% below the nomi-
nal output voltage is detected. A pullup resistor from IN to
FLAG is shown in all schematics.
MIC5206
BYP
is 470pF (see Figure 2). Larger values improve the
BYP
BYP
. Likewise, if rapid turn-on is necessary,
.
BYP
or less and a resonant frequency
, output capacitors of 2.2 F or
BYP
BYP
reduces the regulator phase
) connected from BYP to
BYP
BYP
and leave
is not
6
If an error indication is not required, FLAG may be left open
and the pullup resistor may be omitted.
Enable Pin Ramp and the Error Flag
To prevent indeterminate behavior on the error flag during
power down of the device, ensure that the fall time of the
enable pin signal, from logic high to logic low, is faster than
100 s.
Fixed Regulator Applications
EN (pin 3) is shown connected to IN (pin 1) for an application
where enable/shutdown is not required. The error flag is
shown with a 100k pullup resistor.
Figure 1b is an example of a basic configuration where the
lowest-noise operation is not required. C
The error flag is shown with a 47k pullup resistor.
Ultra-Low-Noise Application
Figure 2 includes a 470pF capacitor for low-noise operation
and shows EN (pin 7) connected to IN (pin 8) for an applica-
tion where enable/shutdown is not required. The error flag is
shown with a 47k pullup resistor.
Adjustable Regulator Applications
Figure 3 shows the MIC5206BMM adjustable output voltage
configuration. Two resistors set the output voltage. The
formula for output voltage is:
Figure 2. Ultra-Low-Noise Fixed Voltage Application
Flag Output
Flag Output
Figure 1a. Low-Noise Fixed Voltage Application
Figure 1b. Low-Noise Fixed Voltage Application
(optional)
(optional)
V
OUT
V
V
EN (pin 3) may be
connected directly
to IN (pin 1).
OUT
OUT
= 1.242V
V
2.2µF
IN
1µF
MIC5206-x.xBM5
1
2
3
1
2
3
4
1
2
3
4
R2
R1
MIC5206-x.xBMM
MIC5206-x.xBMM
1
5
4
47k
47k
BYP
100k
Error Flag
OUT
= 1 F minimum.
V
8
7
6
5
8
7
6
5
January 2000
C
1µF
OUT
OUT
C
470pF
BYP
V
Enable
IN
Micrel
V
IN