Micrel, Inc.
MIC37150/51/52/53
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 MIC37150/51/52/53 requires an output capacitor for
stable
operation.
As
a
µCap
LDO,
the
MIC37150/51/52/53 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 MIC37151 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. The MIC37150/51/52/53
has excellent transient response to variations in input
voltage and load current. The device has been designed
to respond quickly to load current variations and input
voltage variations. Large output capacitors are not
required to obtain this performance. A standard 47µF
output capacitor, is all that is required. Larger values
help to improve performance even further.
Input Capacitor
An input capacitor of 1.0µF or greater is recommended
when the device is more than 4 inches away from the
bulk and 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.
Transient Response and 3.3V to 2.5V, 2.5V to 1.8V or
1.65V, or 2.5V to 1.5V Conversions
The MIC37150/51/52/53 has excellent transient
response to variations in input voltage and load current.
The device has been designed to respond quickly to
9
M9999-101907
Application Information
The MIC37150/51/52/53 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 V
CE
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 MIC37150/51/52/53 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. Transient
protection allows device (and load) survival even when
the input voltage spikes above and below nominal. 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
)
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 Super
October 2007
MICREL [ MICREL SEMICONDUCTOR ]
