Datasheet

MIC5205
DS20005785A-page 10 2017 Microchip Technology Inc.
4.0 APPLICATION INFORMATION
4.1 Enable/Shutdown
Forcing EN (enable/shutdown) high (greater than 2V)
enables the regulator. EN is compatible with CMOS
logic gates.
If the enable/shutdown feature is not required, connect
EN (pin 3) to IN (supply input, pin 1). See Figure 4-1.
4.2 Input Capacitor
A 1 µF capacitor should be placed from IN to GND if
there are more than 10 inches of wire between the
input and the AC filter capacitor or if a battery is used
as the input.
4.3 Reference Bypass Capacitor
BYP (reference bypass) is connected to the internal
voltage reference. A 470 pF capacitor (C
BYP
)
connected from BYP to GND quiets this reference,
providing a significant reduction in output noise. C
BYP
reduces the regulator phase margin; when using C
BYP
,
output capacitors of 2.2 µF or greater are generally
required to maintain stability.
The start-up speed of the MIC5205 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
BYP
.
Likewise, if rapid turn-on is necessary, consider
omitting C
BYP
.
If output noise is not a major concern, omit C
BYP
and
leave BYP open.
4.4 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 µF minimum is
recommended when C
BYP
is not used (see Figure 4-2).
2.2 µF minimum is recommended when C
BYP
is 470 pF
(see Figure 4-1). Larger values improve the 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 or less and a resonant
frequency above 1 MHz. Ultra-low-ESR capacitors can
cause a low amplitude oscillation on the output and/or
underdamped transient response. Most tantalum or
aluminum electrolytic capacitors are adequate; film
types will work, but are more expensive. Because
many aluminum electrolytics have electrolytes that
freeze at about –30°C, solid tantalums are
recommended 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 µF for current below
10 mA or 0.33 µF for currents below 1 mA.
4.5 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.
4.6 Thermal Considerations
The MIC5205 is designed to provide 150 mA of
continuous current in a very small package. Maximum
power dissipation can be calculated based on the
output current and the voltage drop across the part. To
determine the maximum power dissipation of the
package, use the junction-to-ambient thermal
resistance of the device and the following basic
equation:
EQUATION 4-1:
T
J(MAX)
is the maximum junction temperature of the
die, 125°C, and T
A
is the ambient operating
temperature. θ
JA
is layout dependent; Ta b le 4-1 shows
examples of junction-to-ambient thermal resistance for
the MIC5205.
The actual power dissipation of the regulator circuit can
be determined using the equation:
EQUATION 4-2:
Substituting P
D(MAX)
for P
D
and solving for the
operating conditions that are critical to the application
will give the maximum operating conditions for the
TABLE 4-1: SOT-23-5 THERMAL
RESISTANCE
Package
θ
JA
Rec.
Min.
Footprint
θ
JA
Square
Copper
Clad
θ
JC
SOT-23-5
(M5)
220°C/W 170°C/W 130°C/W
P
DMAX
T
JMAX
T
A

JA
-------------------------------------=
P
D
V
IN
V
OUT
I
OUT
V
IN
+ I
GND
=