MIC5367 Datasheet, PDF (7/11 Pages) Micrel Semiconductor – High Performance 200mA Peak LDO in 1.6mm x 1.6mm Thin MLF®

Micrel, Inc.
Application Information
MIC5367 and MIC5368 are Low noise 150mA LDOs.
The MIC5368 includes an auto-discharge circuit that is
switched on when the regulator is disabled through the
Enable pin. The MIC5367/8 regulator is fully protected
from damage due to fault conditions, offering linear
current limiting and thermal shutdown.
Input Capacitor
The MIC5367/8 is a high-performance, high bandwidth
device. An input capacitor of 1µF 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 MIC5367/8 requires an output capacitor of 1µF 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 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 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 MIC5367/8 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
MIC5367/8
Enable/Shutdown
The MIC5367/8 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 a
“zero” off-mode-current state. In this state, current
consumed by the regulator goes nearly to zero. Forcing
the enable pin high enables the output voltage. The
active-high enable pin uses CMOS technology and the
enable pin cannot be left floating; a floating enable pin
may cause an indeterminate state on the output.
Thermal Considerations
The MIC5367/8 is designed to provide 150mA 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 3.3V, the output
voltage is 1.5V, and the output current = 150mA. The
actual power dissipation of the regulator circuit 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 <100µA over the load range, the power
dissipation contributed by the ground current is < 1% and
can be ignored for this calculation.
P_D = (3.3V – 1.5V) × 150mA
P_D = 0.27W
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 = 92.4°C/W for the YMT
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 junction-to-
ambient thermal resistance for the minimum footprint is
92.4°C/W.
The maximum power dissipation must not be exceeded
for proper operation.
June 2010
7
M9999-060110-A