Micrel, Inc.
MIC94161/2/3/4/5
Maximum Current vs.
Ambient Temperature
(1" Square Copper)
Application Information
The MIC94161/2/3/4/5 is a family of high-side load
switches designed to operate from 1.7V to 5.5V input
voltage. The load switch pass element is an internal
14.5mΩ RDSON N-Channel MOSFET which enables the
device to support up to 3A of continuous current.
Additionally, the load switch supports 1.5V logic level
control and shutdown features in a tiny 1.5mm × 1mm
6-ball WLCSP package.
3.5
3
2.5
2
1.5
1
VIN = 5v
VIN = 4v5
VIN = 3v6
VIN=2v5
The MIC9416x provides reverse current protection when
the device is disabled. The device will not allow the flow
of current from the output to the input when the device is
turned OFF. Additionally, the MIC94161 features
overvoltage protection to protect the load when the input
voltage is above 4.55V, as well as a precise enable
threshold which keeps the MIC94161 in the default OFF
state until the EN pin rises above 1.15V.
0.5
0
-60 -40 -20
0
20 40 60 80 100 120 140
AMBIENT TEMPERATURE (°C)
Figure 3. Safe Operating Area (SOA) Graph
Power Dissipation Considerations
The MIC94162/3 features rapid turn on for applications
that require quick startup time. The MIC94161/4/5
provides a slew rate controlled soft-start turn-on of 2.7ms.
The soft-start feature is provided to prevent an in-rush
current event from pulling down the input supply voltage.
As with all power switches, the current rating of the
switch is limited mostly by the thermal properties of the
package and the PCB it is mounted on. There is a simple
ohms law type relationship between thermal resistance,
power dissipation and temperature, which are analogous
to an electrical circuit:
The MIC94162/4 feature an active load discharge circuit
which switches in a 200Ω load when the switch is
disabled to automatically discharge a capacitive load.
An active pull-down on the enable input keeps the
MIC94161/2/3/4/5 in a default OFF state until the enable
pin is pulled above 1.2V. Internal level shift circuitry
allows low voltage logic signals to switch higher supply
voltages. The enable voltage can be as high as 5.5V and
is not limited by the input voltage.
Power Switch SOA
Figure 4. Simple Electrical Circuit
The safe operating area (SOA) curve represents the
boundary of maximum safe operating current and
maximum safe operating junction temperature.
From this simple circuit we can calculate VX if we know
ISOURCE, VZ and the resistor values, RXY and RYZ using
Equation 1:
Figure 3 illustrates the SOA for various input voltages,
with the package mounted on a typical 1 layer, 1 square
inch copper board.
VX = ISOURCE (RXY + RYZ) + VZ
Eq. 1
Thermal circuits can be considered using these same
rules and can be drawn similarly by replacing current
sources with power dissipation (in watts), resistance with
thermal resistance (in °C/W) and voltage sources with
temperature (in °C).
Revision 1.1
March 14, 2014
9