Datasheet

MIC2915X/30X/50X/75X
DS20005685B-page 24  2016-2019 Microchip Technology Inc.
4.0 APPLICATION INFORMATION
The MIC2915x, MIC2930x, MIC2950x, and MIC2975x
are high-performance low-dropout voltage regulators
suitable for all moderate to high-current voltage
regulator applications. Their 350 mV to 425 mV typical
dropout voltage at full load make them 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-emitter
voltage drop and collector-emitter saturation voltage,
dropout performance of the PNP output of these
devices is limited merely by the low VCE saturation
voltage.
A trade-off for the low-dropout voltage is a varying base
driver requirement. But Microchip’s Super ßeta PNP
process reduces this drive requirement to merely 1% of
the load current.
The MIC2915x/2930x/2950x/2975x family of regulators
are fully protected from damage due to fault conditions.
Current limiting is provided. This limiting is linear;
output current under overload conditions is constant.
Thermal shutdown disables the device when the die
temperature exceeds the +125°C maximum safe
operating temperature. Line transient protection allows
device and load survival even when the input voltage
spikes between –20V and +60V. When the input
voltage exceeds approximately 32V, the overvoltage
sensor disables the regulator. The output structure of
these regulators allows voltages in excess of the
desired output voltage to be applied without reverse
current flow. MIC29xx1 and MIC29xx2 versions offer a
logic-level ON/OFF control. When disabled, the
devices draw nearly zero current.
An additional feature of this regulator family is a
common pinout. A design’s current requirement may
change up or down, but use the same board layout
because all of these regulators have identical pinouts.
FIGURE 4-1: Linear Regulators Require
Only Two Capacitors for Operation.
4.1 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
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from
this data sheet.
EQUATION 4-1:
The ground current is approximated by 1% of I
OUT
.
Then the heat sink thermal resistance is determined
with Equation 4-2.
EQUATION 4-2:
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 Super ßeta
PNP regulators allow very significant reductions in
regulator power dissipation and the associated heat
sink without compromising performance. When this
technique is employed, a capacitor of at least 0.1 µF is
needed directly between the input and regulator
ground.
Please refer to Application Note 9 and Application Hint
17 for further details and examples on thermal design
and heat sink specification.
With no heat sink in the application, calculate the
junction temperature to determine the maximum power
dissipation that will be allowed before exceeding the
maximum junction temperature of the MIC29152. The
maximum power allowed can be calculated using the
MIC29xxx
V
IN
IN
V
OUT
OUT
GND
P
D
I
OUT
1.01 V
IN
V
OUT
–=

SA
T
JMAX
T
A
–
P
D
----------------------------

JC

CS
+–=
Where:
T
JMAX
≤ 125°C
θ
CS
Between 0°C/W and 2°C/W