Micrel, Inc.
MIC37300/01/02/03
Where T
J(max)
< 125°C and
θ
CS
is between 0°C and
2°C/W. The heat sink may be significantly reduced in
applications where the minimum input voltage is
known and is large compared with the dropout
voltage. Use a series input resistor to drop excessive
voltage and distribute the heat between this resistor
and the regulator. The low-dropout properties of
Micrel’s Super ßeta PNP® regulators allow significant
reductions in regulator power dissipation and the
associated
heat
sink
without
compromising
performance. When this technique is employed, a
capacitor of at least 1.0µF is needed directly between
the input and regulator ground.
Refer to “Application Note 9” for further details and
examples on thermal design and heat sink
applications.
Output Capacitor
The MIC37300/01/02/03 requires an output capacitor
for stable operation. As a µCap LDO, the
MIC37300/01/02/03 can operate with ceramic output
capacitors as long as the amount of capacitance is
47µF or greater. For values of output capacitance
lower than 47µF, the recommended ESR range is
200mΩ to 2Ω. The minimum value of output
capacitance recommended for the MIC37300 is 10µF.
For 47µF or greater, the ESR range recommended is
less than 1Ω. Ultra-low ESR, ceramic capacitors are
recommended for output capacitance of 47µF or
greater to help improve transient response and noise
reduction at high frequency. 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.
Input Capacitor
An input capacitor of 1.0µF or greater is
recommended when the device is more than 4 inches
away from the bulk supply capacitance, or when the
supply is a battery. Small, surface-mount chip
capacitors can be used for the bypassing. The
capacitor should be place within 1" of the device for
optimal performance. Larger values will help to
improve ripple rejection by bypassing the input to the
regulator, further improving the integrity of the output
voltage.
Applications Information
Enable/Shutdown
The MIC37300/01/02/03 is a high-performance low-
dropout voltage regulator suitable for moderate to
high-current regulator applications. Its 500mV dropout
voltage at full load and over-temperature makes it
especially valuable in battery-powered systems and
as high-efficiency noise
filters
in post-regulator
applications. Unlike older NPN-pass transistor
designs, there the minimum dropout voltage is limited
by the based-to-emitter voltage drop and collector-to-
emitter saturation voltage, dropout performance of the
PNP output of these devices is limited only by the low
VCE saturation voltage.
A trade-off for the low dropout voltage is a varying
base drive requirement. Micrel’s Super ßeta PNP®
process reduces this drive requirement to only 2% to
5% of the load current.
The MIC37300/01/02/03 regulator is fully protected
from damage due to fault conditions. Current limiting
is provided. This limiting is linear; output current
during overload conditions is constant. Thermal
shutdown disables the device when the die
temperature exceeds the maximum safe operating
temperature. The output structure of these regulators
allows voltages in excess of the desired output
voltage to be applied without reverse current
flow.
Thermal Design
Linear regulators are simple to use. The most
complicated design parameters to consider are
thermal characteristics. Thermal design requires the
following application-specific parameters:
•
Maximum ambient temperature (T
A
)
•
Output current (I
OUT
)
•
Output voltage (V
OUT
)
•
Input voltage (V
IN
)
•
Ground current (I
GND
)
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from
this datasheet.
P
D
= (V
IN
– V
OUT
) I
OUT
+ V
IN
I
GND
where the ground current is approximated by using
numbers from the “Electrical Characteristics” or
“Typical Characteristics.” Then the heat sink thermal
resistance is determined with this formula:
θ
SA
= ((T
J(max)
– T
A
)/ P
D
) – (θ
JC
+
θ
CS
)
October 2009
9
M9999-102909
MICREL [ MICREL SEMICONDUCTOR ]
