MIC2003 MICREL [Micrel Semiconductor], MIC2003 Datasheet - Page 11

• Manufacturer Part Number: MIC2003
• Description: Current Limiting Circuit Protector
• Manufacturer: MICREL [Micrel Semiconductor]

October 2005
Functional Description
Input and Output
V
circuitry driving the switch and the input (Source
connection) of the power MOSFET switch. V
Drain connection of the power MOSFET and supplies
power to the load. In a typical circuit, current flows from
V
directional when enabled, if V
current will flow from V
When the switch is disabled, current will not flow to the
load, except for a small unavoidable leakage current of
a few microamps. However, should V
more than a diode drop (~0.6V), while the switch is
disabled, current will flow from output to input via the
power MOSFET’s body diode. This effect can be used
to advantage when large bypass capacitors are placed
on MIC2003/2013’s’s output. When power to the switch
is removed, the output capacitor will be automatically
discharged.
If discharging C
consider using MIC2003/2013 or MIC2007/2017 in place
of MIC2003/2013. These MIC2000 family members are
equipped with a discharge FET to insure complete
discharge of C
Current Sensing and Limiting
MIC2003/2013 protects the system power supply and
load from damage by continuously monitoring current
through the on-chip power MOSFET. Load current is
monitored by means of a current mirror in parallel with
the power MOSFET switch. Current limiting is invoked
when the load exceeds an internally set over-current
threshold. When current limiting is activated the output
current is constrained to the limit value, and remains at
this level until either the load/fault is removed, the load’s
current requirement drops below the limiting value, or
the MIC2003/2013 goes into thermal shutdown.
Kickstart (MIC2013 only)
The MIC2013 is designed to allow momentary current
surges (Kickstart) before the onset of current limiting,
which permits dynamic loads, such as small disk drives
or portable printers to draw the energy needed to
overcome inertial loads without sacrificing system
safety. In this respect, the MIC2013 differs markedly
from MIC2003 and its peers, which immediately limit
load current, potentially starving the motor and causing
the appliance to stall or stutter.
During this delay period, typically 128 ms, a secondary
current limit is in effect. If the load demands a current in
excess the secondary limit, MIC2013 acts immediately
to restrict output current to the secondary limit for the
IN
IN
is both the power supply connection for the internal
to V
OUT
toward the load. Since the switch is bi-
LOAD
LOAD
.
OUT
is required by your application,
to V
IN
OUT
.
is greater than V
OUT
exceed V
OUT
is the
IN
by
IN
,
11
duration of the Kickstart period. After this time the
MIC2013 reverts to its normal current limit. An example
of Kickstart operation is shown below.
A) MIC2013 is enabled into an excessive load (slew
B) R
C) Kickstart period.
D) Current limiting initiated. FAULT/ goes LOW.
E) V
F) Thermal shutdown followed by thermal cycling.
G) Excessive load released, normal load remains.
H) FAULT/ delay period followed by FAULT/ going
Slew Rate Control
Large capacitive loads can create significant current
surges when charged through a high-side switch such
as the MIC2003/2013. For this reason, MIC2003/2013
provides built-in slew rate control to limit the initial inrush
currents upon enabling the power MOSFET switch.
Slew rate control is active upon powering up, and upon
re-enabling the load. At shutdown, the discharge slew
rate is controlled by the external load and output
capacitor.
Picture Key:
rate limiting not visible at this time scale) The initial
current surge is limited by either the overall circuit
resistance and power supply compliance, or the
secondary current limit, whichever is less.
heating (effect exaggerated for emphasis).
where V
for dead shorts).
MIC2013 drops out of current limiting.
HIGH.
O
O
U
OUT
ON
U
T
T
of the power FET increases due to internal
is non-zero (load is heavy, but not a dead short
Figure 3. Kickstart Operation
OUT
= 0. Limiting response will be the same
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