MIC29302HWU Datasheet, PDF (8/10 Pages) Micrel Semiconductor – High-Current Low-Dropout Regulators

Micrel, Inc.
Application Information
The MIC29302HWU is a high-performance low-dropout
voltage regulator suitable for moderate to high-current
voltage regulator applications. The 350mV to 425mV
typical dropout voltage at full load 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-emitter
voltage drop and collector-emitter saturation voltage,
dropout performance of the PNP output of these devices
is limited merely by the low V_CE saturation voltage.
A trade-off for the low-dropout voltage is a varying base
driver requirement. But Micrel’s Super ßeta PNP^®
process reduces this drive requirement to merely 1% of
the load current.
The MIC29302HWU regulator is 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
40V, the over voltage 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. The MIC29302HWU
versions offer a logic level ON/OFF control: when
disabled, the devices draw nearly zero current.
Figure 1. Linear Regulators Require Only
Two Capacitors for Operation
MIC29302HWU
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, we calculate the power dissipation of the regulator
from these numbers and the device parameters from this
datasheet.
P_D  I_OUT 1.01 V_IN  V_OUT 
Eq. 1
where the ground current is approximated by 1% of I_OUT.
Then the heat sink thermal resistance is determined with
 _SA

T_JMAX  T_A
P_D
 _JC
 _CS 
Eq.
2
:
 _SA

T_JMAX  T_A
P_D
 _JC
 _CS 
Eq. 2
where TJMAX ≤ 125°C and θCS is between 0 and
2°C/W.
For example, given an expected maximum ambient
temperature (TA) of 75C with VIN = 3.3V, VOUT =
2.5V, and IOUT = 1.5A, first calculate the expected PD
using Eq. 3:
P_D=(3.3V–2.5V)1.5A–(3.3V)(0.016A)=1.1472W
Eq. 3
Next, calcualte the junction temperature for the expected
power dissipation.
T_J=(θ_JA×P_D)+T_A=(56C/W×1.1472W)+75C
=139.24C
Eq. 4
November 11, 2013
8
Revision 1.0