NCP4547

http://onsemi.com

8

APPLICATIONS INFORMATION

On−Resistance

The MOSFET gate voltage in the NCP4547 is driven by

a charge pump in the controller circuit. The output voltage

Enable Control

The NCP4547 allows for enabling the MOSFET in either

an active-high or active-low configuration. When the EN

and POL pins are both at a logic high level or both at a logic

applied, the MOSFET will be enabled. Similarly, when the

EN and POL pins are at different logic levels, the MOSFET

will be disabled.

An internal pull down resistor on the EN pin and an

internal pull up resistor on the POL pin ensure that the

MOSFET will be disabled when neither pin is driven. The

internal pull down or pull up resistor can also be used to

allow for only one of the pins to be driven in either an

active-high or active-low state.

Parametric Adjustments

The NCP4547 can be used in several configurations

depending on the need to control turn-on delay, slew rate, and

bleed resistance. Default minimum values of each parameter

are built into the part without the requirement of external

components. This configuration is shown above in Figure 1.

Figures 22 and 23 show alternate configurations where

external components are used to modify the turn-on delay,

slew rate, and total bleed resistance.

pins. This allows for one external capacitor to be used to

modify the turn-on delay and slew rate. Note that the value

Figure 23 shows the use of two external capacitors for

independent control of the turn-on delay and slew rate.

Turn−On Delay

The NCP4547 provides a time delay between the input

transitions on EN (or POL) to the MOSFET turning on. The

turn-on delay can be increased with an external capacitor

added between the DELAY pin and either ground or the

The total delay is calculated by adding the default turn-on

delay to a delta term which is calculated as follows:

(eq. 1)

capacitance added between the DELAY pin to either ground

capacitor is present, the delay will be the specified default

turn-on delay.

Slew Rate Control

The NCP4547 is equipped with controlled output slew

rate which provides soft start functionality. This limits the

inrush current caused by capacitor charging and enables this

device to be used in hot swapping applications. The slew rate

can be decreased with an external capacitor added between

The slew rate can be calculated as follows:

SR +

(eq. 2)

the on-chip capacitance (see table below). Note that this

capacitor is present, the slew rate will be the specified

default slew rate.

Load Bleed

The NCP4547 has an on−chip bleed resistor that can be

used to bleed the charge off of the load to ground after the

MOSFET has been disabled. In series with the bleed resistor

is a bleed switch which is enabled whenever the MOSFET

is disabled. Delays are added to the enable of this switch to

ensure that both the MOSFET and the bleed switch are not

concurrently active. The total bleed resistance can be

increased by adding a resistor between the BLEED pin and

bleed function is not desired, the BLEED pin should be tied

to ground or left floating.

SLEW RATE AND TURN−ON DELAY

Parameter

Conditions

Symbol

Min

Typ

Max

Unit

Turn−on Delay Constant

1.65

MW

External Delay Capacitance (Note 10)

Between DEL pin and GND

10

nF

Slew Rate Constant

1.43

mA

External Slew Rate Capacitance (Note 10)

2

nF

Internal Slew Rate Capacitance

150

pF

External Combo Capacitance (Note 10)

2

nF

10.Recommended range, larger values may be used but may degrade the performance of the part