NCV8512(2008) Ver la hoja de datos (PDF) - ON Semiconductor

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NCV8512
(Rev.:2008)

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

ON Semiconductor 

NCV8512

CIRCUIT DESCRIPTION

VIN

VOUT

DELAY

RESET Threshold

1.8V VDT

0.45V VLD

RESET

Td

Td

Power on Input Under−voltage

Reset V Dip

Secondary Output

Spike Overload

Figure 11. Reset and Delay Circuit Wave Forms

REGULATOR CONTROL FUNCTIONS

The NCV8512 contains a microprocessor−compatible

control function RESET (Figure 11).

RESET Function

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

powers up. After VOUT increases above the RESET

threshold, the DELAY timer is started. When the DELAY

timer passes 1.8 V, the RESET signal goes high. A discharge

of the DELAY timer is started when VOUT drops and stays

below the RESET threshold. When the DELAY timer level

drops below 0.45 V, the RESET signal is brought low.

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 VRL can be decreased from a typical

value of 4.65 V to as low as 3.5 V by using an external

voltage divider connected from VOUT to the pin RADJ as

displayed in Figure 12. The resistor divider keeps the

voltage above the VRADJ.TH (typical 1.31 V) and overrides

the internal threshold detector. Adjust the voltage divider

according to the following relationship:

VTHRES + VRADJ.TH

RADJ1 ) RADJ2

RADJ2

(2)

Where;

VTHRES is the desired output threshold voltage that starts

the time delay for Power on Reset Delay.

VRADJ.TH is the default threshold voltage of 1.31 V typ.

RADJ1 is the resistor connected from the 5 V output to the

RADJ pin.

RADJ2 is the resistor connected from the RADJ pin to

ground.

If the reset adjust option is not needed, the RADJ pin

should be connected to GND causing the reset threshold to

go to its default value (4.65 V typical).

As an example, select resistors to give a threshold voltage

of 4.0 V. This will allow the delay timer to start when the

output crosses the 4.0 V level.

VTHRES = 4.0 V = 1.31 V x (RADJ1 + RADJ2) / RADJ2

Let RADJ2 be 100 kW for low current consumption.

RADJ1 = 2.05 x 100 k = 205 kW

With 5 V on the output, the voltage on the RADJ pin will

be 1.64 V.

RADJ1

RADJ2

RADJ

VOUT

NCV8512

RRST

to mP and

System

Power

COUT

Delay

RESET

CDELAY

6.4 V

to mP and

RESET

Port

Figure 12. Adjustable RESET

DELAY Function

The reset delay circuit provides a delay (programmable by

external capacitor) on the RESET output lead.

The DELAY lead provides source current (typically 9 mA)

to the external DELAY capacitor at the following times:

1. During Power Up (once the regulation threshold

has been exceeded).

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