MIC5524 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – High-Performance 500mA LDO

Micrel, Inc.
Application Information
The MIC5524 is a high-performance, low-power 500mA
LDO. The MIC5524 includes an auto-discharge circuit
that is switched on when the regulator is disabled through
the enable pin. The MIC5524 also offers an internal
pulldown resistor on the enable pin to ensure the output
is disabled if the control signal is tri-stated. The MIC5524
regulator is fully protected from damage due to fault
conditions, offering linear current limiting and thermal
shutdown.
Input Capacitor
The MIC5524 is a high-performance, high-bandwidth
device. An input capacitor of 2.2µF 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.
Output Capacitor
The MIC5524 requires an output capacitor of 2.2µF 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 2.2µF 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.
No-Load Stability
Unlike many other voltage regulators, the MIC5524
remains stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
MIC5524
Enable/Shutdown
The MIC5524 comes with an active-high enable pin that
allows the regulator to be disabled. Forcing the enable
pin low disables the regulator and sends it into an off
mode current state drawing virtually zero current. When
disabled the MIC5524 switches an internal 25Ω load on
the regulator output to discharge the external capacitor.
Forcing the enable pin high enables the output voltage.
The MIC5524 has an internal pull down resistor on the
enable pin to disable the output when the enable pin is
floating.
Thermal Considerations
The MIC5524 is designed to provide 500mA 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 3.3V, and the output current = 500mA. The
actual power dissipation of the regulator circuit can be
determined using Equation 1:
P_D = (V_IN − V_OUT)I_OUT + V_IN I_GND
Eq. 1
Because this device is CMOS and the ground current is
typically <100µA over the load range, the power
dissipation contributed by the ground current is <1% and
can be ignored Equation 2:
P_D = (3.6V − 3.3V)× 500mA
P_D = 0.150W
Eq. 2
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance of the device Equation 3:
P_D(MAX)
=

T_J(MAX) −
θ_JA
T_A

Eq. 3
T_J(MAX) = 125°C, the maximum junction temperature of the
die, θ_JA thermal resistance = 250°C/W for the TDFN
package.
May 15, 2013
8
Revision 1.0