MIC5304 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – Single 150mA Low Operating Current LDO with Dual Voltage Pin Select

Micrel, Inc.
MIC5304
Application Information
The MIC5304 is a low quiescent current voltage selectable
LDO. The regulator is capable of sourcing 150mA of output
current with a low quiescent current of 24µA. A logic input
signal selects the output between two preset voltages. The
MIC5304 regulator is fully protected from damage due to
fault conditions, offering linear current limiting and thermal
shutdown.
Input Capacitor
The MIC5304 is a high-performance, high bandwidth device.
Therefore, it requires a well bypassed input supply for
optimal performance. 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 MIC5304 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.
Enable/Shutdown
The MIC5304 is provided with an active-high enable pin that
allows the regulator to be enabled. 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. 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.
Voltage Select
The voltage select pin is used to select the output voltage
between two voltages. A logic high signal sets the output to
the higher voltage; while a logic low signal selects the lower
output voltage. The voltage select pin cannot be left floating;
a floating pin may cause an indeterminate state on the
output.
Thermal Considerations
The MIC5304 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
3.15V with V_SEL set high and 1.85V with V_SEL low, and the
output current = 150mA. The lower output voltage should be
used for power dissipation calculations as this is the worst
case situation. The actual power dissipation of the regulator
circuit can be determined using the equation:
P_D = (V_IN – V_OUT) 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 –1.85V) × 150mA
P_D = 0.2625W
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 = 92°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°C/W.
The maximum power dissipation must not be exceeded for
proper operation.
For example, when operating the MIC5304-XDYMT at an
input voltage of 3.6V and 150mA load with a minimum
footprint layout, the maximum ambient operating
temperature T_A can be determined as follows:
0.2625W = (125°C – T_A)/(92°C/W)
T_A = 100°C
Therefore, a 3.15/1.85V application with a 150mA output
current can accept an ambient operating temperature of
100°C in a 1.6mm x 1.6mm MLF^® package. For a full
discussion of heat sinking and thermal effects on voltage
regulators, refer to the “Regulator Thermals” section of
Micrel’s Designing with Low-Dropout Voltage Regulators
handbook. This information can be found on Micrel's website
at: http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
November 2008
9
M9999-111908-A