MIC5326 Datasheet, PDF (7/10 Pages) Micrel Semiconductor – 150mA Low Operating Current LDO

Micrel, Inc.
Applications Information
The MIC5326 is a low quiescent current, low dropout
regulator designed for optimal performance in a small
space. The MIC5326 regulator is fully protected from
damage due to fault conditions, offering linear current
limiting and thermal shutdown.
Input Supply Voltage
V_IN provides the supply to power the LDO. The minimum
input voltage is 2.3V allowing conversion from typical
lithium ion batteries and low voltage supplies.
Input Capacitor
The MIC5326 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 with
minimum space required. Additional high frequency
capacitors, such as small value NPO dielectric type
capacitors, help filter out high frequency noise and are
good practice in any RF circuit.
Output Capacitor
The MIC5326 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.
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. 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.
Minimum Load Current
The MIC5326 does not require a minimum load to
maintain output voltage regulation.
Enable/ Shutdown
The MIC5326 comes with an active high enable pin that
enables the regulator. 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 cannot be left floating; a
floating enable pin may cause an unknown output state.
MIC5326
Thermal Considerations
The MIC5326 is designed to provide 150mA continuous
output current from a very small footprint package.
Maximum ambient operating temperature can be
calculated based on the output current and the voltage
drop across the part. For example: given that the input
voltage is 3.6V, the output voltage is 2.8V and the output
current is 150mA. The 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) × 150mA
P_D = 0.12W
To determine the maximum ambient operating
temperature 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
⎟⎟⎠⎞
The maximum junction temperature of the die, T_J(max) =
125°C.The package thermal resistance, θ_JA = 173°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 maximum power dissipation must not be exceeded
for proper operation.
For example, when operating the MIC5326 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:
0.12W = (125°C – T_A)/(173°C/W)
T_A = 104.24°C
Therefore a 2.8V 150mA application can accept an
ambient operating temperature of 104.24°C in a 1.2mm
x 1.6mm Thin 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
October 2008
7
M9999-100808-A