AOZ1300
Detailed Description
The AOZ1300 is a high-side, current-limited, N-channel
MOSFET switch optimized for power distribution
applications which require circuit protection. The device
operates from 2.7V to
6.0V
input voltage and offers
current limiting and thermal overload protection. The
device can be programmed for load current up to 4A
using a single resistor. An open-drain fault output is
provided to indicate over-current and thermal overload
fault conditions. The AOZ1300’s soft-start circuitry
minimizes the inrush current in applications that employ
highly capacitive loads. The output slew-rate may be
increased with an external capacitor if longer soft-start
time is desired. The AOZ1300 features a circuit breaker
mode that latches the output off upon detecting an over-
current condition lasting more than 24ms or detecting a
thermal overload condition. The AOZ1300 features
reverse current blocking function. Therefore, the output
voltage can be higher than the input voltage.
output shuts off, it remains off until the fault load is
removed from output and the EN input is toggled or the
input power is recycled. If the fault is still present after EN
has been cycled, the AOZ1300 will again shut off all
power to the load after 24ms.
Thermal Overload Protection
The thermal overload protection of AOZ1300 is engaged
to protect the device from damage should the die
temperature exceeds safe margins due to a short circuit,
extreme loading or heating from external sources.
Thermal overload protection sets a fault latch and shuts
off the internal MOSFET and asserts the FLT output if the
junction temperature exceeds +120°C. The AOZ1300 can
be re-enabled by toggling EN pin or cycling the input
supply after the die temperature drops below +110°C.
Fault Indicator
The FLT pin is an open drain output that is asserted low
when either an over-current, short-circuit or thermal
overload condition occurs. To prevent false alarm, the
AOZ1300 implements a 24ms fault blanking time for
over-current and short-circuit fault conditions. The FLT
pin becomes high impedance when the fault conditions
are removed. A 100k
Ω
pull-up resistor must be
connected between FLT to V
IN
to provide a logic signal.
Enable
The EN pin is the ON/OFF control for the output switch.
It is an active-high input. The EN pin is active after V
IN
is
above the UVLO threshold of 2.3V. Conversely, the
Enable will be de-activated if the V
IN
falls below the
UVLO of 2.0V. The EN pin must be driven to a logic high
or logic low state to guarantee operation. While disabled,
the AOZ1300 only draws about 1µA supply current. The
EN is a high impedance input with an ESD protection
diode to ground and should not be forced below ground.
This input level is compatible with most microcontroller
outputs and other logic families.
Slew Rate Control
The output voltage rise time is controlled to a minimum of
400µs and is controlled by an internal slew-rate limiting
circuit. The slew-rate can be increased by placing a
capacitor between SLEW and ground. As a result, longer
rise times can be achieved for specific applications. The
slew rate is independent from the load. Please see Slew
Rate Setting section for detailed information.
Under-Voltage Lockout (UVLO)
The under-voltage lockout (UVLO) circuit of AOZ1300
monitors the input voltage and prevents the output
MOSFET from turning on until V
IN
exceeds 2.3V. The
AOZ1300 will trigger a fault condition and shut down
the device when V
IN
falls below 2.0V.
Applications Information
Input and Output Capacitor Selection
The input capacitor prevents large voltage transients
from appearing at the input, and provides the instanta-
neous current needed each time the switch turns on
and to limit input voltage droop. Also it is to prevent
high-frequency noise on the power line from passing
through the output of the power side. The choice of the
input capacitor is based on its ripple current and voltage
ratings rather than its capacitor value. The input capacitor
should be a low ESR type and located as close to the
V
IN
pin as possible. A 0.1µF 6.3V ceramic cap is
recommended. However, higher capacitor values further
reduce the voltage drop at the input.
Over-Current and Short-Circuit Protection
The AOZ1300 is designed to shut off all power to the load
when the output current exceeds the limit for more than
the fault blanking period. In the event of an output short
circuit the current through the switch is limited by an
internal current-limiting amplifier. The current-limit circuit
employs a current- sensing algorithm that uses the
on-state resistance of the high-side MOSFET as a
current-sensing element. If the current-sense voltage is
above the current-limit threshold, the AOZ1300 will turn
off the internal MOSFET. The AOZ1300 has a very fast
short-circuit response time, nominally 25µs. Once the
Rev. 1.3
August
2008
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