MIC2033 Datasheet, PDF (13/20 Pages) Micrel Semiconductor – High-Accuracy, High-Side, Fixed Current Limit Power Switch

Micrel, Inc.
Functional Description
The MIC2033 is a high-side MOSFET power distribution
switch providing increased system reliability utilizing 5%
current limit accuracy. The MIC2033 has an operating
input voltage range from 2.5V to 5.5V and is internally
current limited and has thermal shutdown that protects
the device and system.
Soft-Start
Soft-start reduces the power supply input surge current
at startup by controlling the output voltage rise time. The
input surge appears while the output capacitor is
charged up. A slower output rise time will draw a lower
input surge current.
During soft-start, an internal current sink discharges the
external capacitor at CSLEW to ground to control the
ramp of the output voltage. The output voltage rise time
is dependent upon the value of C_CSLEW, the input voltage,
output voltage, and the current limit. The value of the
CSLEW external capacitor is recommended to be in the
range of 0.1µF to 1µF.
Input Capacitor
A 1µF to 10µF ceramic input capacitor is recommended
for most applications.
The input capacitor must be placed on the same side of
the board and next to the MIC2033 to minimize the
voltage ringing during transient and short circuit
conditions. It is also recommended to use two vias for
each end of the capacitor to connect to the power and
ground plane.
X7R or X5R dielectric 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 or a tantalum capacitor to ensure the
same capacitance value over the operating temperature
range.
Output Capacitor
The output capacitor type and placement criteria are the
same as the input capacitor. See the Input Capacitor
section for a detailed description.
Enable
The MIC2033 offers either an active high or active low
enable input (EN) that allows ON/OFF control of the
switch output. The current through the device reduces to
near “zero” when the device is shutdown, with only
microamperes of leakage current. The EN input may be
MIC2033
directly tied to V_IN or driven by a voltage that is equal to
or less than V_IN, but do not leave this pin floating.
Current Limit
The MIC2033 is available with four fixed current limit
settings: 0.5A, 0.8A, 1A, and 1.2A. If the output current
exceeds the set current limit, then the MIC2033 switch
will enter constant current limit mode. The maximum
allowable current limit may be less than the full specified
and/or expected current if the MIC2033 is not mounted
on a circuit board with sufficiently low thermal resistance.
The MIC2033 responds within 10µs to short circuits to
limit the output current and also provides an output fault
flag that will assert (low) for an over current condition
that lasts longer than 32ms.
Thermal Design
To help reduce the thermal resistance, the ePad
(underneath the IC) should be soldered to the PCB
ground and the placement of thermal vias either
underneath or near the ePad is highly recommended.
Thermal design requires the following application-
specific parameters:
 Maximum ambient temperature (T_A)
 Output current (I_OUT)
 Input voltage (V_IN)
 Current Limit (I_LIMIT)
When the MIC2033 is in constant current limit mode, it
may exceed the over temperature threshold. If this
occurs, the over temperature condition will shut down
the MIC2033 switch and the fault status flag will go
active (assert low). After the switch cools down, it will
turn on again. The MIC2033 power dissipation can be
maximized by either lowering the thermal resistance on
the exposed pad (only the DFN package has an
exposed pad) on the printed circuit board, or by limiting
the maximum allowable ambient temperature.
Thermal Measurements
It is always wise to measure the IC’s case temperature
to make sure that it is within its operating limits. Although
this might seem like a very elementary task, it is very
easy to get erroneous results. The most common
mistake is to use the standard thermal couple that
comes with the thermal voltage meter. This thermal
couple wire gauge is large, typically 22 gauge, and
behaves like a heatsink, resulting in a lower case
measurement.
There are two suggested methods for measuring the IC
case temperature: a thermal couple or an infrared
thermometer. If a thermal couple is used, it must be
constructed of 36 gauge wire or higher to minimize the
wire heatsinking effect. In addition, the thermal couple tip
must be covered in either thermal grease or thermal glue
August 2012
13
M9999-082012-A