Datasheet

MIC5501/2/3/4
DS20006006A-page 10  2018 Microchip Technology Inc.
4.0 APPLICATION INFORMATION
MIC5501/2/3/4 are low-noise 300 mA LDOs. The
MIC5502 and MIC5504 include an auto-discharge
circuit that is switched on when the regulator is
disabled through the enable (EN) pin. The MIC5503
and MIC5504 have an internal pull-down resistor on the
EN pin to ensure the output is disabled if the control
signal is tri-stated. The MIC5501/2/3/4 regulators are
fully protected from damage due to fault conditions,
offering linear current limiting and thermal shutdown.
4.1 Input Capacitor
The MIC5501/2/3/4 are high performance, high
bandwidth devices. An input capacitor of 1 µF is
required from the input to ground to provide stability.
Low-ESR ceramic capacitors provide optimal
performance at a minimum of space. Additional high
frequency capacitors, such as small-valued NPO
dielectric-type capacitors, help filter out high frequency
noise and are good practice in any RF-based circuit.
X5R or X7R dielectrics are recommended for the input
capacitor. Y5V dielectrics lose most of their
capacitance over temperature and are therefore, not
recommended.
4.2 Output Capacitor
The MIC5501/2/3/4 require an output capacitor of 1 µF
or greater to maintain stability. The design is optimized
for use with low-ESR ceramic chip capacitors. High
ESR capacitors are not recommended because they
may cause high frequency oscillation. The output
capacitor can be increased, but performance has been
optimized for a 1 µF ceramic output capacitor and does
not improve significantly with larger capacitance.
X7R/X5R dielectric-type ceramic capacitors are
recommended because of their temperature
performance. X7R-type capacitors change capacitance
by 15% over their operating temperature range and are
the most stable type of ceramic capacitors. Z5U and
Y5V dielectric capacitors change value by as much as
50% and 60%, respectively, over their operating
temperature ranges. To use a ceramic chip capacitor
with Y5V dielectric, the value must be much higher than
an X7R ceramic capacitor to ensure the same
minimum capacitance over the equivalent operating
temperature range.
4.3 No-Load Stability
Unlike many other voltage regulators, the
MIC5501/2/3/4 remain stable and in regulation with no
load. This is especially important in CMOS RAM
keep-alive applications.
4.4 Enable/Shutdown
The MIC5501/2/3/4 each come with an active-high
enable pin that allows the regulator to be disabled.
Forcing the EN pin low disables the regulator and
sends it into an off mode current state drawing virtually
zero current. When disabled, the MIC5502 and
MIC5504 switches an internal 25 load on the
regulator output to discharge the external capacitor.
Forcing the EN pin high enables the output voltage.
The MIC5501 and MIC5502 enable pin uses CMOS
technology and the EN pin cannot be left floating; a
floating EN pin may cause an indeterminate state on
the output. The MIC5503 and MIC5504 have an
internal pull-down resistor on the enable pin to disable
the output when the enable pin is floating.
4.5 Thermal Considerations
The MIC5501/2/3/4 are designed to provide 300 mA of
continuous current in a very small package. Maximum
ambient operating temperature can be calculated
based on the output current and the voltage drop
across the part. For example if the input voltage is 3.6V,
the output voltage is 2.8V, and the output current is
300 mA. The actual power dissipation of the regulator
circuit can be determined using Equation 4-1:
EQUATION 4-1:
Because this device is CMOS and the ground current
is typically <100 µA over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation:
EQUATION 4-2:
To determine the maximum ambient operating
temperature of the package, use the
junction-to-ambient thermal resistance of the device
and Equation 4-3:
EQUATION 4-3:
P
D
V
IN
V
OUT1
–I
OUT
 V
IN
+ I
GND
=
P
D
3.6V 2.8 V–300mA 0.240W==
P
DMAX
T
JMAX
T
A
–

JA
--------------------------------
=
Where:
T
J(MAX)
= 125°C, the max. junction temp. of the die.

JA
= Thermal resistance of 250°C/W for the DFN
package.