MIC2075-1YM 查看數據表（PDF） - Micrel
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MIC2075-1YM Datasheet PDF : 14 Pages
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MIC2025/2075
Block Diagram
EN
OSC.
CHARGE
PUMP
THERMAL
SHUTDOWN
UVLO
1.2V
REFERENCE
IN
GATE
CONTROL
CURRENT
LIMIT
FLAG
RESPONSE
DELAY
OUT
FLG
GND
Micrel, Inc.
Functional Description
Input and Output
IN is the power supply connection to the logic circuitry and
the drain of the output MOSFET. OUT is the source of the
output MOSFET. In a typical circuit, current flows from IN to
OUT toward the load. If VOUT is greater than VIN, current will
flow from OUT to IN since the switch is bidirectional when
enabled. The output MOSFET and driver circuitry are also
designed to allow the MOSFET source to be externally forced
to a higher voltage than the drain (VOUT > VIN) when the
switch is disabled. In this situation, the MIC2025/75 avoids
undesirable current flow from OUT to IN.
Thermal Shutdown
Thermal shutdown is employed to protect the device from
damage should the die temperature exceed safe margins
due mainly to short circuit faults. Each channel employs its
own thermal sensor. Thermal shutdown shuts off the output
MOSFET and asserts the FLG output if the die temperature
reaches 140°C. The MIC2025 will automatically reset its output
should the die temperature cool down to 120°C. The MIC2025
output and FLG signal will continue to cycle on and off until
the device is disabled or the fault is removed. Figure 2 depicts
typical timing. If the MIC2075 goes into thermal shutdown, its
output will latch off and a pull-up current source is activated.
This allows the output latch to automatically reset when the
load (such as a USB device) is removed. The output can also
be reset by toggling EN. Refer to Figure 1 for details.
Depending on PCB layout, package, ambient temperature,
etc., it may take several hundred milliseconds from the in-
cidence of the fault to the output MOSFET being shut off.
The worst-case scenario of thermal shutdown is that of a
short-circuit fault and is shown in the in the “Function Char-
acteristics: Thermal Shutdown Response” graph.
Power Dissipation
The device’s junction temperature depends on several fac-
tors such as the load, PCB layout, ambient temperature
and package type. Equations that can be used to calculate
power dissipation of each channel and junction temperature
are found below.
PD = RDS(on) × IOUT2
Total power dissipation of the device will be the summation of
PD for both channels. To relate this to junction temperature,
the following equation can be used:
TJ = PD × θJA + TA
where:
TJ = junction temperature
TA = ambient temperature
θJA = is the thermal resistance of the package
Current Sensing and Limiting
The current-limit threshold is preset internally. The preset
level prevents damage to the device and external load but
still allows a minimum current of 500mA to be delivered to
the load.
The current-limit circuit senses a portion of the output MOSFET
switch current. The current-sense resistor shown in the block
diagram is virtual and has no voltage drop. The reaction to
an overcurrent condition varies with three scenarios:
Switch Enabled into Short-Circuit
If a switch is enabled into a heavy load or short-circuit, the
switch immediately enters into a constant-current mode,
reducing the output voltage. The FLG signal is asserted
indicating an overcurrent condition. See the Short-Circuit
Response graph under Functional Characteristics.
June 2010
9
MIC2025/2075
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