AOZ1300AI datasheet(7/12 Pages) AOSMD

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AOZ1300

Rev. 1.

3 August 2008

www.aosmd.com

Page 7 of 12

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.

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 VIN is

above the UVLO threshold of 2.3V. Conversely, the

Enable will be de-activated if the VIN 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.

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 VIN exceeds 2.3V. The

AOZ1300 will trigger a fault condition and shut down

the device when VIN falls below 2.0V.

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

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 VIN to provide a logic signal.

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.

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

VIN pin as possible. A 0.1µF 6.3V ceramic cap is

recommended. However, higher capacitor values further

reduce the voltage drop at the input.

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