MIC5201_05 Datasheet, PDF (8/9 Pages) Micrel Semiconductor – 200mA Low-Dropout Regulator

MIC5201
Applications Information
Figure 1 shows a basic fixed-voltage application with the
unused enable input connected to V_IN.
MIC5201-x.xBM
MIC5201-x.xBS
V_IN
IN
OUT
V_OUT
EN
GND
1µF
Figure 1. Fixed Application
Adjustable regulators require two resistors to set the output
voltage. See Figure 2.
MIC5201BM
V_IN
IN
OUT
V_OUT
EN ADJ R1
GND
3.3µF
R2
V_OUT = 1.242V ^{}1+ ^{RR21}
Figure 2. Adjustable Application
Resistors values are not critical because ADJ (adjust) has a
high impedance, but for best results use resistors of 470kΩ
or less.
Output Capacitors
A 1µF capacitor is recommended between the MIC5201
output and ground to prevent oscillations due to instability.
Larger values serve to improve the regulator’s transient
response. Most types of tantalum or aluminum electrolytics
will be adequate; film types will work, but are costly and
therefore not recommended. Many aluminum electrolytics
have electrolytes that freeze at about –30°C, so solid tanta-
lums are recommended for operation below –25°C. The
important parameters of the capacitor are an effective series
resistance of about 5Ω or less and a resonant frequency
above 500kHz. The value of this capacitor may be increased
without limit.
At lower values of output current, less output capacitance is
required for output stability. The capacitor can be reduced to
0.47µF for current below 10mA or 0.33µF for currents below
1mA.
Input Capacitors
A 1µF capacitor should be placed from the MIC5201 input to
ground 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.
Noise Reduction Capacitors
On adjustable devices, a capacitor from ADJ to GND will
decrease high-frequency noise on the output. See Figure 3.
MIC5201BM
V_IN
IN
OUT
EN ADJ R1
GND
R2
Micrel, Inc.
V_OUT
3.3µF
C_ADJ
Figure 3. Decreasing Ouput Noise
Minimum Load
The MIC5201 will remain stable and in regulation with no
load unlike many other voltage regulators. This is
especially important in CMOS RAM keep-alive
applications.
Dual-Supply Systems
When used in dual supply systems where the regulator
load is returned to a negative supply, the output voltage
must be diode clamped to ground.
Thermal Considerations Layout
The MIC5201-x.xBM (8-pin surface mount package) has the
following thermal characteristics when mounted on a single
layer copper-clad printed circuit board.
PC Board
Dielectric
FR4
Ceramic
θ_JA
160ºC/W
120ºC/W
Multilayer boards having a ground plane, wide traces near the
pads, and large supply bus lines provide better thermal
conductivity.
The “worst case” value of 160°C/W assumes no ground
plane, minimum trace widths, and a FR4 material board.
Nominal Power Dissipation and Die Temperature
The MIC5201-x.xBM at a 25°C ambient temperature will
operate reliably at up to 625mW power dissipation when
mounted in the “worst case” manner described above. At an
ambient temperature of 55°C, the device may safely dissi-
pate 440mW. These power levels are equivalent to a die
temperature of 125°C, the recommended maximum tem-
perature for non-military grade silicon integrated circuits.
For MIC5201-x.xBS (SOT-223 package) heat sink character-
istics, please refer to Micrel Application Hint 17, P.C. Board
Heat Sinking.
50 mil
245 mil
150 mil
MIC5201
30 mil
50 mil
Figure 4. Min. Recommended SO-8 PCB Pads Size
8
June 2005