NCV4279BDWR2 データシートの表示（PDF） - ON Semiconductor

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NCV4279BDWR2

5.0 V Micropower 150 mA LDO Linear Regulator with DELAY, Adjustable RESET, and Monitor FLAG

ON Semiconductor 

NCV4279B

CIRCUIT DESCRIPTION

REGULATOR CONTROL FUNCTIONS

The NCV4279B contains the microprocessor compatible

control function RESET (Figure 11).

VIN

VOUT

DELAY

RESET

RESET

Threshold

DELAY

Threshold

(VDT)

Td

Td

Figure 11. Reset and Delay Circuit Wave Forms

RESET Function

A RESET signal (low voltage) is generated as the IC

powers up until VOUT is within 6.0% of the regulated output

voltage, or when VOUT drops out of regulation,and is lower

than 8.0% below the regulated output voltage. Hysteresis is

included in the function to minimize oscillations.

The RESET output is an open collector NPN transistor,

controlled by a low voltage detection circuit. The circuit is

functionally independent of the rest of the IC thereby

guaranteeing that the RESET signal is valid for VOUT as low

as 1.0 V.

Adjustable Reset Function

The reset threshold can be made lower by connecting an

external resistor divider to the RADJ lead from the VOUT

lead, as displayed in Figure 12. This lead is grounded to

select the default value of 4.6 V.

DELAY Function

The reset delay circuit provides a programmable (by

external capacitor) delay on the RESET output lead.

The DELAY lead provides source current (typically

2.5 mA) to the external DELAY capacitor during the

following proceedings:

1. During Power Up (once the regulation threshold

has been verified).

2. After a reset event has occurred and the device is

back in regulation. The DELAY capacitor is

discharged when the regulation (RESET threshold)

has been violated. This is a latched incident. The

capacitor will fully discharge and wait for the

device to regulate before going through the delay

time event again.

FLAG/Monitor Function

An on−chip comparator is provided to perform an early

warning to the microprocessor of a possible reset signal. The

reset signal typically turns the microprocessor off

instantaneously. This can cause unpredictable results with

the microprocessor. The signal received from the FLAG pin

will allow the microprocessor time to complete its present

task before shutting down. This function is performed by a

comparator referenced to the bandgap reference. The actual

trip point can be programmed externally using a resistor

divider to the input monitor (MON) (Figure 13). The typical

threshold is 1.20 V on the MON Pin.

VBAT

VIN

VOUT

NCV4279B

MON FLAG

VCC

COUT

µP

I/O

RADJ

VOUT

NCV4279B

RRST

to µP and

System

Power

COUT

RADJ RESET

Delay GND

RESET

Figure 13. FLAG/Monitor Function

Delay

RESET

CDELAY

to µP and

RESET

Port

Figure 12. Adjustable RESET

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