MIC5303 Datasheet, PDF (7/8 Pages) Micrel Semiconductor – Single 300mA CMOS Ultra Small ULDO

Micrel, Inc.
MIC5303
Application Information
Enable/Shutdown
The MIC5303 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.
Input Capacitor
The MIC5303 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 perfor-
mance 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.
Output Capacitor
The MIC5303 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.
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 – 2.8V) × 300mA
P_D = 0.24W
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:
⎛ ^TJ(MAX) ^{- T}A
⎝ ^{PD(MAX) =}
JA
T_J(max) = 125°C, the maximum junction temperature of
the die θ_JA thermal resistance = 173°C/W.
The table below shows junction-to-ambient thermal
resistance for the MIC5303 in the 4-pin 1.2mm x 1.6mm
MLF^® package.
Package
4-Pin 1.2x1.6 MLF^®
θ_JA Recommended
Minimum Footprint
173°C/W
Thermal Resistance
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.
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
173°C/W.
The maximum power dissipation must not be exceeded
for proper operation.
For example, when operating the MIC5303-2.8YML at
an input voltage of 3.6V and 300mA load with a
minimum footprint layout, the maximum ambient
operating temperature T_A can be determined as follows:
No-Load Stability
0.24W = (125°C – T_A)/(173°C/W)
Unlike many other voltage regulators, the MIC5303 will
T_A=83°C
remain stable and in regulation with no load. This is
especially important in CMOS RAM keep-alive
applications.
Therefore, a 2.8V application with 300mA of output
current can accept an ambient operating temperature of
83°C in a 1.2mm x 1.6mm MLF^® package. For a full
Thermal Considerations
The MIC5303 is designed to provide 300mA of
continuous current. Maximum ambient operating
temperature can be calculated based on the output
current and the voltage drop across the part. Given that
the input voltage is 3.6V, the output voltage is 2.8V and
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
the output current = 300mA.
October 2006
7
M9999-102506-B