MIC5370_11 Datasheet, PDF (9/13 Pages) Micrel Semiconductor – High-Performance Dual 150mA LDO 1.6mm x 1.6mm Thin MLF®

Micrel, Inc.
MIC5370/1
Application Information
MIC5370/1 is a dual 150mA LDO in a small 1.6mm x
1.6mm package.. The MIC5371 includes an auto-
discharge circuit for each of the LDO outputs that are
activated when the output is disabled. The MIC5370/1
regulator is fully protected from damage due to fault
conditions through linear current limiting and thermal
shutdown.
Input Capacitor
The MIC5370/1 is a high-performance, high bandwidth
device. An input capacitor of 1µF capacitor 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 MIC5370/1 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 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 MIC5370/1 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
Enable/Shutdown
The MIC5370/1 comes with two active-high enable pins
that allow each regulator to be disabled independently.
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.
When disabled the MIC5371 switches a 30Ω (typical)
load on the regulator output to discharge the external
capacitor.
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 MIC5370/1 is designed to provide 150mA of
continuous current for both outputs 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 for V_OUT1, 1.8V
for V_OUT2 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_OUT1 + (V_IN – V_OUT2) I _OUT2 + 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 + (3.6V - 1.8) × 150mA
P_D = 0.39W
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, and the maximum junction temperature
of the die, θ_JA, thermal resistance = 90°C/W.
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
90°C/W.
The maximum power dissipation must not be exceeded
for proper operation.
May 2011
9
M9999-052011-C