MIC2039 Datasheet, PDF (14/21 Pages) Micrel Semiconductor – High-Accuracy, High-Side, Adjustable Current Limit Power Switch

Micrel, Inc.
Functional Description
The MIC2039 is a high-side MOSFET power-distribution
switch that provides increased system reliability by using
5% current limit accuracy. The MIC2039 is internally
current limited and has thermal shutdown, which
protects the device and system.
The MIC2039 has a soft-start circuit that minimizes in-
rush current by slowing the turn-on time. Additionally, the
MIC2039 has an optional Kickstart feature, which
momentarily overrides the normal current-limiting
function to allow higher inrush and/or transient currents.
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 draws a lower
input surge current.
KICKSTART Inrush Overcurrent Filter
The MIC2039EYxx and MIC2039FYxx are equipped with
a secondary current limit that allows high inrush current
transients to pass for a set period before the primary
current-limit circuitry becomes active. The FAULT/ status
flag does not assert during the Kickstart period (typically
120ms), which eliminates any false (FAULT/) assertions.
The Kickstart function is active during initial startup or
while operating in steady state.
Input Capacitor
Micrel recommends a 1µF to 10µF ceramic input
capacitor for most applications.
Place the input capacitor on the same side of the board
and next to the MIC2039 to minimize the voltage ringing
during transient and short-circuit conditions. Using two
vias for each end of the capacitor to connect to the
power and ground plane is also recommended.
Micrel recommends X7R or X5R dielectric ceramic
capacitors 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.
MIC2039
Output Capacitor
The output capacitor type and placement criteria are the
same as for the input capacitor. See the “Input
Capacitor” section for a detailed description.
Enable
The MIC2039 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 shut down, with only
microamperes of leakage current. The EN input can be
directly tied to V_IN or driven by a voltage that is equal to
or less than V_IN; do not leave this pin floating.
Adjustable Current Limit
The MIC2039 current limit is adjustable from 0.2A to
2.5A by connecting a resistor from the ILIMIT pin to
GND. The following equation determines the resistor:
RLIMIT ≅ 289 / ILIMIT
Eq. 1
where I_LIMIT is the typical current limit from the electrical
table. If the output current exceeds the set current limit,
the MIC2039 switch enters constant current limit mode.
The maximum allowable current limit can be less than
the full specified and/or expected current if the MIC2039
is not mounted on a circuit board with sufficiently low
thermal resistance. Table 1 shows resistor values (1%)
for select current limit settings.
ILIMIT
RLIMIT
0.2A
1.45kΩ
0.5A
576Ω
1.0A
287Ω
2A
145Ω
2.5A
115Ω
Table 1. Resistor Selection for Adjustable Current Limit
June 7, 2013
14
Revision 1.1