MIC5375 Datasheet, PDF (8/18 Pages) Micrel Semiconductor – High Performance Low Dropout 150mA LDO

Micrel, Inc.
Application Information
MIC5375/6/7/8 is Low noise 150mA LDO. The
MIC5376/8 includes an auto-discharge circuit that is
switched on when the regulator is disabled through the
enable pin. The MIC5375/6/7/8 regulator is protected
from damage due to fault conditions, offering linear
current limiting and thermal shutdown.
Input Capacitor
The MIC5375/6/7/8 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
For output voltages ≥ 2.5V, the MIC5375/6/7/8 requires
a minimum 1µF output capacitor. For output voltages
below 2.5V a 2.2µF minimum output capacitor is
required. 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 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 MIC5375/6/7/8
will remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
MIC5375/6/7/8
Enable/Shutdown
The MIC5375/6/7/8 is provided 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.
Adjustable Regulator Design
The MIC5377/8 adjustable version allows setting the
output voltage down to 1V with the use of two external
feedback resistors.
J1
VIN
J5
EN
J2
GND
C1
2.2µF
6.3V
U1 MIC5377/8-xxYMT
2 _{VIN VOUT} 3
1 _EN
ADJ ⁷
GND
4,5,6,8
C2
2.2µF
6.3V
R1
619k
R2
267k
J3
VOUT
J4
GND
V_OUT
=
V_{REF ⎜⎜⎝⎛}1 +
R₁
R₂
⎟⎟⎠⎞
Thermal Considerations
The MIC5375/6/7/8 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 3.6V, the output
voltage is 2.8V, 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 = (3.6V – 2.8V) × 150mA
P_D = 0.12W
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 = 250°C/W for the YMT
package and 256.5°C/W for the SC-70-5 package.
January 2009
8
M9999-011309-B