MIC2009YM6 TX Micrel Inc, MIC2009YM6 TX Datasheet - Page 11

• Manufacturer Part Number: MIC2009YM6 TX
• Manufacturer: Micrel Inc

Specifications of MIC2009YM6 TX

• Short Circuit Current Limit: 0.2 to 2A
• Input Voltage Range: 2.5 to 5.5V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 6
• Package Type: SOT-23
• Lead Free Status / RoHS Status: Compliant

September 2005
Micrel
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 MIC2009/2019’s’s output. When power to the switch
is removed, the output capacitor will be automatically
discharged.
If discharging C
consider using MIC2004/2014 or MIC2007/2017 in place
of MIC2009/2019. These MIC2000 family members are
equipped with a discharge FET to insure complete
discharge of C
Current Sensing and Limiting
The MIC2009/2019 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 externally 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 MIC2009/2019 goes into
thermal shutdown.
Kickstart (MIC2019 only)
The MIC2019 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 MIC2019 differs markedly
from MIC2009 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 of the secondary limit, the MIC2019 acts
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
immediately to restrict output current to the secondary
limit for the duration of the Kickstart period. After this
time, the MIC2019 reverts to its normal current limit. An
example of Kickstart operation is shown below.
A) MIC2019 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
Under Voltage Lock Out
Under voltage lock-out insures no anomalous operation
occurs before the device’s minimum input voltage of
2.5V had been achieved. Prior to reaching this voltage,
the output switch (power MOSFET) is OFF and no
circuit functions, such as FAULT/ or ENABLE, are
considered to be valid or operative.
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).
MIC2019 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
MIC2009/MIC2019
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M9999-092305