MIC5333 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Micro-Power High Performance Dual 300mA ULDO™ with Dual POR

Micrel, Inc.
MIC5333
Application Information
MIC5333 is a dual 300mA LDO, with an integrated
Power On Reset (POR) for each of the regulators. The
MIC5333 regulator is fully protected from damage due to
fault conditions, offering linear current limiting and
thermal shutdown.
Input Capacitor
The MIC5333 is a high-performance, high bandwidth
device. Therefore, it requires a well-bypassed input
supply for optimal performance. A 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 MIC5333 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 MIC5333 will
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
Enable/Shutdown
The MIC5333 comes with dual 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.
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.
Power On Reset
Each of the regulator outputs has a Power On Reset
status pin (POR1/POR2). This pin is an open drain
output. When an LDO is enabled an active low POR
indicates an under voltage condition on V_OUT.
Each POR status signal can be programmed for a delay
of 1sec/µF by placing a capacitor from its associated
CSET pin to ground. Where the CSET1 pin sets the
delay for the POR1 output and the CSET2 pin sets the
delay for the POR2 output. Zero delay is added by
leaving the CSET1/2 pin open circuit.
Thermal Considerations
The MIC5333 is designed to provide 300mA 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 3.0V for V_OUT1, 2.8V
for V_OUT2 and the 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 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 – 3.0V) × 300mA + (3.6V -2.8) × 300mA
P_D = 0.42W
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 = 75°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
75°C/W.
The maximum power dissipation must not be exceeded
for proper operation.
For example, when operating the MIC5333-PMYMT at
an input voltage of 3.6V and 300mA loads at each output
with a minimum footprint layout, the maximum ambient
operating temperature T_A can be determined as follows:
February 2008
8
M9999-021408-A