MIC5385 Datasheet, PDF (9/13 Pages) Micrel Semiconductor – Ultra Small Triple 150mA Output LDO

Micrel, Inc.
Application Information
MIC5385 is a triple output Low noise 150mA LDO. The
MIC5385 regulator is fully protected from damage due to
fault conditions, offering linear current limiting and
thermal shutdown.
Input Capacitor
The MIC5385 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 MIC5385 requires an output capacitor of 1µF or
greater for each output 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 MIC5385 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
MIC5385
Enable/Shutdown
The MIC5385 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 MIC5385 is designed to provide three outputs up to
150mA each 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 and the output voltages are 3.3V,1.8V,
and 1.5V each with an output current = 150mA. The
actual power dissipation of the regulator circuit can be
determined using the equation:
P_D = (V_IN – V_OUT1) I _OUT1 +
(V_IN – V_OUT2) I _OUT2 +
(V_IN – V_OUT3) I _OUT + V_IN I_GND
As the MIC5385 is a CMOS device, the ground current is
typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1% and
may be ignored for this calculation.
P_D = (3.6V – 3.3V)150mA+(3.6V-1.8V)150mA+
(3.6V-1.5V)150mA
P_D = 0.63W
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, and θ_JA thermal resistance = 90°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.
December 2009
9
M9999-122109-A