MIC5373 Datasheet, PDF (15/19 Pages) Micrel Semiconductor – Triple 200mA μCap LDO in 2.5 x 2.5 Thin MLF

Micrel, Inc.
Application Information
MIC5373/83 is a triple output device with three 200mA
LDOs. The MIC5373/83 incorporates a POR function
with the capability to monitor any voltage using POR_IN.
The monitored voltage can be set to any voltage
threshold level to trigger the POR flag. A delay on the
POR flag may also be set with an external capacitor at
the DLY pin. All the LDOs have current limit and thermal
shutdown protection to prevent damage from fault
conditions. MIC5373 has active high enables while the
MIC5383 has active low enables.
Input Capacitor
The MIC5373/83 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 MIC5373/83 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 MIC5373/83
will remain stable and in regulation with no load.
Thermal Considerations
The MIC5373/83 is designed to provide three outputs up
to 200mA each of continuous current in a very small
package. Maximum ambient operating temperature can
MIC5373/83
be calculated based on the output current and the
voltage drop across the part. For example if the input
voltages are 3.6V and the output voltages are 3.3V,
2.5V, and 1.8V each with an output current = 150mA.
The actual power dissipation of the regulator circuit can
be determined using the equation:
P_D = (V_INLDO1/2 – V_OUT1) I _OUT1 +
(V_INLDO1/2 – V_OUT2) I _OUT2 +
(V_INLDO3 – V_OUT3) I _OUT3 + V_IN x I_GND
As the MIC5373/83 is a CMOS device, the ground current
is typically <100µA over the load range, the power
dissipation contributed by the ground current is < 1% and
may be ignored for this calculation.
P_D ≈ (3.6V – 2.8V)150mA+(3.6V-1.8V)150mA+
(3.6V-1.2V)150mA
P_D ≈ 0.75W
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 = 100°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 MIC5373-MG4YMT at
an input voltage of 3.6V and 150mA load on LDO1,
LDO2 and LDO3 with a minimum layout footprint, the
maximum ambient operating temperature T_A can be
determined as follows:
0.75W = (125°C – T_A) / (100°C/W)
T_A = 50°C
Therefore the maximum ambient operating temperature
of 50°C is allowed in a 2.5mm x 2.5mm Thin MLF^®
package for the voltage options specified and at the
maximum load of 150mA on each output. 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
July 2010
15
M9999-070110