LM3525

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SNVS051D – FEBRUARY 2000 – REVISED MARCH 2013

FUNCTIONAL DESCRIPTION

The LM3525-H and LM3525-L are high side P-Channel switches with active-high and active-low enable inputs,

respectively. Fault conditions turn off and inhibit turn-on of the output transistor and activate the open-drain error

flag transistor sinking current to the ground.

INPUT AND OUTPUT

IN (Input) is the power supply connection to the control circuitry and the source of the output MOSFET.

OUT (Output) is the drain of the output MOSFET. In a typical application circuit, current flows through the switch

from IN to OUT towards the load.

bidirectional.

THERMAL SHUTDOWN

LM3525 is internally protected against excessive power dissipation. In the event of a shorted output or heavy

loads that could elevate the die temperature to above approximately 135°C, the thermal shutdown circuit of the

LM3525 will be activated and the power switch turned off.

The switch is turned on after die temperature drops by 10°C. This built-in temperature hysteresis prevents

undesirable oscillation of the thermal protection circuit and allows the device to reset itself after it is cooled down.

UNDERVOLTAGE LOCKOUT

UVLO prevents the MOSFET switch from turning on until input voltage exceeds 1.9V.

UVLO shuts off the MOSFET switch and signals the fault flag if input voltage drops below 1.8V. UVLO functions

only when device is enabled.

CURRENT LIMIT

The current limit circuit is designed to protect the system supply, the MOSFET switches and the load from

damage caused by excessive currents. The current limit threshold is set internally to allow a minimum of 500 mA

through the MOSFET but limit the maximum current to 1.0A typical.

FAULT FLAG

The fault flag is an open-drain output capable of sinking 10 mA load current to typically 60 mV above ground.

The fault flag is active (pulled low) when any of the following conditions are present: undervoltage, current limit,

or thermal shutdown.

A 1ms delay in reporting fault condition prevents erroneous fault flags and eliminates the need for external RC

delay network.

Application Information

FILTERING

The USB specification indicates that “no less than 120 µF tantalum capacitors” must be used on the output of

each downstream port. This bulk capacitance provides the short-term transient current needed during a hot plug-

in. Current surges caused by the input capacitance of the down stream device could generate undesirable EMI

signals. Ferrite beads in series with all power and ground lines are recommended to eliminate or significantly

reduce EMI.

In selecting a ferrite bead, the DC resistance of the wire used must be kept to minimum to reduce the voltage

drop.

EMI damage to other components during the hot - detachment.

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