NCV8512(2008) データシートの表示（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

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. When the DELAY capacitor

discharges to 0.45 V, the RESET signal pulls low.

FLAG/Monitor Function

An on−chip comparator is available to provide 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 voltage. 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

RM1

RM2

VIN

VOUT

NCV8512

MON FLAG

RADJ RESET

Delay GND

RFLG

VCC

COUT

mP

I/O

RRST

RESET

Figure 13. FLAG/Monitor Function

APPLICATION NOTES

FLAG MONITOR

Figure 14 shows the FLAG Monitor waveforms taken

from the circuit depicted in Figure 13. As the output voltage

falls (VOUT), the Monitor threshold is crossed. This causes

the voltage on the FLAG output to go low sending a warning

signal to the microprocessor that a RESET signal may occur

in a short period of time. TWARNING is the time the

microprocessor has to complete the function it is currently

working on and get ready for the RESET shutdown signal.

VOUT

MON

FLAG Monitor

Ref. Voltage

RESET

FLAG

Use the typical value for VDT = 1.8 V.

Use the typical value for Delay Charge Current = 9.0 mA.

ƪ33 nF(1.8 * 0.04 V)ƫ

tDELAY +

9.0 mA

+ 6.45 ms

STABILITY CONSIDERATIONS

The output or compensation capacitor helps determine

three main characteristics of a linear regulator: startup delay,

load transient response and loop stability.

The capacitor value and type should be based on cost,

availability, size and temperature constraints. A tantalum or

aluminum electrolytic capacitor is best, since a film or

ceramic capacitor with almost zero ESR can cause

instability. The aluminum electrolytic capacitor is the least

expensive solution, but, if the circuit operates at low

temperatures (−25°C to −40°C), both the value and ESR of

the capacitor will vary considerably. The capacitor

manufacturer’s data sheet usually provides this information.

The value for the output capacitor COUT shown in Figure 15

should work for most applications, but is not necessarily the

optimized solution.

TWARNING

Figure 14. FLAG Monitor Circuit Waveform

SETTING THE DELAY TIME

The delay time is controlled by the Reset Delay Low

Voltage, Delay Switching Threshold, and the Delay Charge

Current. The delay follows the equation:

tDELAY

+

ƪCDELAY(VDT * Reset Delay Low

Delay Charge Current

Voltage)ƫ

Example:

Using CDELAY = 33 nF.

Use the typical value for Delay Low Voltage = 0.04 V.

VIN

CIN*

0.1 mF

VOUT

NCV8512

RESET

RRST

COUT**

10 mF

*CIN required if regulator is located far from the power supply filter.

**COUT required for stability. Capacitor must operate at minimum

temperature expected.

Figure 15. Test and Application Circuit Showing

Output Compensation

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