9 Revision 2.0
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 Capacitance
In order to maintain stability, the MIC94310 requires an
output capacitor of 0.47µF or greater for the Thin DFN
and CSP packages and 10µF or greater for the SOT-23
package. For optimal ripple rejection performance a 1µF
capacitor is recommended for the CSP and Thin DFN
packages, while a 10µF capacitor is recommended for
the SOT-23 package. 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.
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:
PD = (VIN – VOUT1) IOUT + VIN IGND
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.
PD = (2.5V – 1.8V) × 200mA
PD = 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:
−
=
JA
AJ(max)
D(MAX) θ
TT
P
TJ(MAX) = 125ºC, the maximum junction temperature of the
die, θJA thermal resistance = 173°C/W for the Thin DFN
package.
Substituting PD for PD(MAX) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit.
For proper operation, the maximum power dissipation
must not be exceeded.
For example, when operating the MIC94310-GYMT at an
input voltage of 2.5V and 200mA load with a minimum