mic39151 Micrel Semiconductor, mic39151 Datasheet - Page 9

• Manufacturer Part Number: mic39151
• Description: Mic39150/mic39151 1.5a Low-voltage Low-dropout Regulator
• Manufacturer: Micrel Semiconductor

Application Information
The MIC39150/1 is a high-performance low-dropout
voltage regulator suitable for moderate to high-current
voltage regulator applications. Its 500mV dropout
voltage at full load and overtemperature makes it
especially valuable in battery-powered systems and as
high-efficiency noise filters in post-regulator applications.
Unlike older NPN-pass transistor designs, where the
minimum dropout voltage is limited by the base-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 βeta PNP™ process
reduces this drive requirement to only 2% to 5% of the
load current. The MIC39150/1 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:
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from this
datasheet.
Micrel, Inc.
May 2006
• Maximum ambient temperature (T
• Output Current (I
• Output Voltage (V
• Input Voltage (V
• Ground Current (I
P
D
Figure 1. Capacitor Requirements
=
V
(V
IN
C
IN
IN
−
V
OUT
IN
IN
MIC39150-x.x
OUT
)
GND
OUT
I )
GND
)
)
)
OUT
OUT
+
V
IN
I
C
GND
OU T
V
A
OU T
)
9
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:
Where T
The heat sink June 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
βeta 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 1µF 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 specification.
Output Capacitor
The MIC39150/1 requires an output capacitor to
maintain stability and improve transient response.
Proper capacitor selection is important to ensure proper
operation. TheMIC39150/1 output capacitor selection is
dependent upon the ESR (equivalent series resistance)
of the output capacitor to maintain stability. When the
output capacitor is 10µF or greater, the output capacitor
should have an ESR less than 2Ω. This will improve
transient response as well as promote stability. Ultralow
ESR capacitors (<100mΩ), such as ceramic chip
capacitors June promote instability. These very low ESR
levels June cause an oscillation and/or underdamped
transient response. A low-ESR solid tantalum capacitor
works extremely well and provides good transient
response and stability over temperature. Aluminum
electrolytics can also be used, as long as the ESR of the
capacitor is < 2Ω.
The value of the output capacitor can be increased
without limit. Higher capacitance values help to improve
transient response and ripple rejection and reduce
output noise.
Input Capacitor
An input capacitor of 1µF or greater is recommended
when the device is more than 4 inches away from the
bulk ac supply capacitance, or when the supply is a
battery. Small, surface-mount, ceramic chip capacitors
can be used for the bypassing. The capacitor should be
placed 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.
θ
J(max)
SA
=
≤ 125°C and θ
T
J(max)
P
D
−
T
A
−
CS
(
θ
is between 0° and 2°C/W.
JC
+
θ
CS
MIC39150/39151
)
[phone]
M9999-053106