MIC94310 Datasheet, PDF (9/13 Pages) Micrel Semiconductor – 200mA LDO with Ripple Blocker™ Technology

Micrel, Inc.
Application Information
The MIC94310 is a very-high PSRR, fixed-output,
200mA LDO utilizing Ripple Blocker™ technology. The
MIC94310 is fully protected from damage due to fault
conditions, offering linear current limiting and thermal
shutdown.
Input Capacitor
The MIC94310 is a high-performance, high-bandwidth
device. An input capacitor of 0.47µF 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
In order to maintain stability, the MIC94310 requires an
output capacitor of 0.47µF or greater. For optimal ripple
rejection performance a 1µF capacitor is recommended.
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 1µF 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 their value by as much
as 50% and 60%, respectively, over their operating
temperature ranges. To use a ceramic chip capacitor
with the 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
The MIC94310 will remain stable and in regulation with
no load. This is especially important in CMOS RAM
keep-alive applications.
MIC94310
Enable/Shutdown
Forcing the enable (EN) pin low disables the MIC94310
and sends it into a “zero” off mode current state. In this
state, current consumed by the MIC94310 goes nearly to
zero. Forcing EN high enables the output voltage. The
EN pin uses CMOS technology and cannot be left
floating as it could cause an indeterminate state on the
output.
Thermal Considerations
The MIC94310 is designed to provide 200mA 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 2.5V, the output
voltage is 1.8V, and the output current = 200mA. The
actual power dissipation of the Ripple Blocker™ can be
determined using the equation:
P_D = (V_IN – V_OUT1) I _OUT + V_IN I_GND
Because this device is CMOS and the ground current is
typically <170µA over the load range, the power
dissipation contributed by the ground current is <1% and
can be ignored for this calculation.
P_D = (2.5V – 1.8V) × 200mA
P_D = 0.14W
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance of the device and the following basic
equation:
P_D(MAX)
=
⎜⎜⎝⎛
T − _J(max)
θ _JA
T_A
⎟⎟⎠⎞
T_J(max) = 125°C, the maximum junction temperature of the
die, θ_JA thermal resistance = 173°C/W for the Thin MLF^®
package.
Substituting P_D for P_D(MAX) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit.
The maximum power dissipation must not be exceeded
for proper operation.
February 2012
9
M9999-020612-A