MIC5338 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Dual 300mA μCap LDO in 1.6mm x 1.6mm Thin MLF®

Micrel, Inc.
Application Information
MIC5338/9 is a dual 300mA LDO. The MIC5339
includes an auto-discharge circuit for each LDO output
that is activated when the output is disabled. The
MIC5338/9 regulator is fully protected from damage due
to fault conditions through linear current limiting and
thermal shutdown.
Input Capacitor
The MIC5338/9 is a high performance, high bandwidth
device. An input capacitor of 1µF from the input pin to
ground is required to provide stability. Low ESR ceramic
capacitors provide optimal performance in small board
area. 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 MIC5338/9 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 and X5R dielectric ceramic capacitors are
recommended because of their temperature
performance. X7R 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 MIC5338/9 will
remain stable and in regulation with no load.
MIC5338/9
Enable/Shutdown
The MIC5338/9 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 an off mode current state drawing virtually
zero current. When disabled, the MIC5339 switches an
internal 30Ω 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
cannot be left floating. A floating enable pin may cause
an indeterminate state on the output.
Thermal Considerations
The MIC5338/9 is designed to provide two 300mA
continuous current outputs in a very small package.
Maximum operating temperature can be calculated
based on the output currents and the voltage drop
across the part. For example, if the input voltage is 3.6V,
V_OUT1 = 3.3V, V_OUT2 = 2.8V and each with an output
current = 300mA. 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 is CMOS device and the ground current is
typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1%
which can be ignored for this calculation.
P_D = (3.6V – 3.3V) × 300mA + (3.6V – 2.8V) × 300mA
P_D = 0.33W
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
θ_JA = 92.4°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
92.4°C/W.
The maximum power dissipation must not be exceeded
for proper operation.
June 2010
8
M9999-063010-A