Micrel, Inc.
MIC5374/84
will remain stable and in regulation with no load.
Application Information
MIC5374/84 is a four output device with three 200mA
LDOs and a 1mA RTC LDO. The MIC5374/84
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.
MIC5374 has active high enables while the MIC5384 has
active low enables.
Thermal Considerations
The MIC5374/84 is designed to provide three outputs up
to 200mA each 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
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:
PD = (VINLDO1/2 – VOUT1) I OUT1
(VINLDO1/2 – VOUT2) I OUT2
+
RTC LDO
+
LDO4 is an always-on RTC LDO used for application
processor support and can provide 1mA of output
current. Power must be provided to the INLDO4 and
BIAS pins to keep LDO4 enabled.
(VINLDO3 – VOUT3) I OUT3
+
(VINLDO4 – VOUT4) I OUT4 + VIN x IGND
As the MIC5374/84 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. Since LDO4 only
supplies 1mA of current, it can also be ignored for this
calculation.
Input Capacitor
The MIC5374/84 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.
PD ≈ (3.6V – 3.3V)150mA+(3.6V-2.5V)150mA+
(3.6V-1.8V)150mA
PD ≈ 0.48W
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:
Output Capacitor
T
− TA
⎛
⎜
⎜
⎝
⎞
⎟
⎟
⎠
J(MAX)
The MIC5374/84 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.
PD(MAX)
=
θJA
TJ(MAX) = 125°C
θ
JA = 100°C/W
Substituting PD for PD(max) and solving for the ambient
operating temperature will give the maximum operating
conditions for the regulator circuit.
X7R and X5R dielectric ceramic capacitors are
The maximum power dissipation must not be exceeded
for proper operation.
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.
For example, when operating the MIC5374-SJG1YMT 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 TA can be
determined as follows:
0.48W = (125°C – TA) / (100°C/W)
TA = 77°C
Therefore the maximum ambient operating temperature
of 77°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
No Load Stability
Unlike many other voltage regulators, the MIC5374/84
M9999-070110
July 2010
17
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