MIC5317 Datasheet, PDF (9/17 Pages) Micrel Semiconductor – High-Performance Single 150mA LDO

Micrel, Inc.
Application Information
MIC5317 is a low-noise 150mA LDO. The MIC5317
regulator is fully protected from damage due to fault
conditions, offering linear current limiting and thermal
shutdown.
Input Capacitor
The MIC5317 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 MIC5317 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 MIC5317 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
MIC5317
Enable/Shutdown
The MIC5317 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 MIC5317 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 3.6V, the output
voltage is 2.8V, and the output current = 150mA. The
actual power dissipation of the regulator circuit can be
determined using Equation 1:
P_D = (V_IN – V_OUT1) 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 for Equation 2:
P_D = (3.6V – 2.8V) × 150mA
P_D = 0.120W
Eq. 2
To determine the maximum ambient operating
temperature of the package, use the junction-to-ambient
thermal resistance of the device and Equation 3:
P_D(MAX)
=

T_J(max) − T_A
θ _JA

Eq. 3
T_J(max) = 125°C, the maximum junction temperature of the
die, θ_JA thermal resistance = 240°C/W for the YMT
package, and 253°C/W for the SOT23-5 and TSOT23-5
packages.
August 23, 2013
9
Revision 1.0