MIC2073 Datasheet, PDF (11/16 Pages) Micrel Semiconductor – Dual-Channel Power Distribution Switch

Micrel, Inc.
Block Diagram
MIC2073/2074
MIC2073/2074 Block Diagram
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 when the switch is
enabled.
An important consideration in a choosing switch is
whether it has “reverse voltage protection” that is, does
not have a body diode. Reverse voltage protection is
important when the switch is disabled and a voltage is
presented to the OUT pin that is greater than the VIN
voltage. The reverse voltage protection prevents current
flow in the reverse path from OUT to IN.
On other hand when the switch is enabled the switch is
bidirectional. In this case when a voltage is presented to
the OUT pin that is greater than the VIN voltage, current
will flow from OUT to IN.
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 (V_OUT > V_IN)
when the switch is disabled. In this situation, the
MIC2073/2074 prevents 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 and the
overheated channel is in current limit. The other channel
is not affected. If however, the die temperature exceeds
160°C, then both channels will be shut off. Upon
determining a thermal shutdown condition, the MIC2074
will latch the output off. In this case, 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 timing details.
The MIC2073 will automatically reset its output when the
die temperature cools down to 120°C. The MIC2073
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.
Depending upon PCB layout package, ambient
temperature, etc., it may take several hundred
milliseconds from the incidence of the fault to the output
MOSFET being shut off. This time will be shortest in the
case of a dead short on the output.
January 2009
11
M9999-011209