NCP458R, NCP459

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FUNCTIONAL DESCRIPTION

Overview

The NCP458R and NCP459 are high side N channel

MOSFET power distribution switch designed to isolate ICs

connected on the battery or DCDC supplies in order to save

energy. The part can be used with a wide range of supply

from 0.75 V to 5.5 V.

Enable Input

Enable pin is an active high. The path is opened when EN

pin is tied low (disable), forcing NMOS switch off.

min, Vin min and EN forced to high level.

Auto Discharge (Optional − NCP459)

NMOS FET is placed between the output pin and GND,

in order to discharge the application capacitor connected on

OUT pin.

The auto−discharge is activated when EN pin is set to low

level (disable state).

The discharge path ( Pull down NMOS) stays activated as

long as EN pin is set at low level.

In order to limit the current across the internal discharge

Vbias Rail

The core of the IC is supplied thanks to Vbias supply rail

(common +5 V, 3.3 V, 1.8 V, 1.2 V). Indeed, no current

consumption is used on IN pin, allowing to improve power

saving of the rail that must be isolated by the power switch.

If Vbias rail is not available or used, Vbias pin and Vin pin

can be connected together as close as possible the DUT. A

minimum of 1.2 V is necessary to control the IC.

Output rise time − Gate control

The NMOS is control with internal charge pump and

driver. A minimum gate slew rate is internally set to avoid

huge inrush current when EN is set from low to high. The

default gate slew rate depends on Vin level. The higher Vin

level, the longer rise time.

In addition, an external capacitor can be connected

between Gate pin and GND in order to slow down the gate

rising. See electrical table for more details.

Cin and Cout Capacitors

100 nF external capacitors must be connected as close as

possible the DUT for noise immunity and better stability. In

case of input hot plug (input voltage connected with fast

slew rate − few

ms − it’s strongly recommended to avoid big

capacitor connected on the input. That allows to avoid input

over voltage transients.

Reverse Blocking Control (Optional NCP458R)

A reverse blocking control circuitry is embedded to

eliminate leakages from OUT to IN in case of Vout > Vin.

A comparator measures the dropout voltage on the switch

between OUT and IN and turn off the NMOS if this voltage

exceeds specified reverse voltage.