NCV8141

http://onsemi.com

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DEFINITION OF TERMS

Dropout Voltage: The input−output voltage differential

at which the circuit ceases to regulate against further

reduction in input voltage. Measured when the output

voltage has dropped 100 mV from the nominal value

obtained at 14 V input, dropout voltage is dependent upon

load current and junction temperature.

Input Voltage: The DC voltage applied to the input

terminals with respect to ground.

Line Regulation: The change in output voltage for a

change in the input voltage. The measurement is made under

conditions of low dissipation or by using pulse techniques

such that the average chip temperature is not significantly

affected.

Load Regulation: The change in output voltage for a

change in load current at constant chip temperature.

Quiescent Current: The part of the positive input current

that does not contribute to the positive load current. The

regulator ground lead current.

Ripple Rejection: The ratio of the peak−to−peak input

ripple voltage to the peak−to−peak output ripple voltage.

Current Limit: Peak current that can be delivered to the

output.

CIRCUIT DESCRIPTION

The NCV8141 is a 5.0 V Watchdog Regulator with

protection circuitry and three logic control functions that

allow a microprocessor to control its own power supply. The

NCV8141 is designed for use in automotive, switch mode

power supply post regulator, and battery powered systems.

Basic regulator performance characteristics include a low

noise, low drift, 5.0 V

±4.0% precision output voltage with

short circuit, thermal, and overvoltage protection make it

possible to use this regulator in particularly harsh operating

environments.

The Watchdog logic function monitors an input signal

(WDI) from the microprocessor or other signal source.

When the signal frequency goes below the externally

programmable limit, a RESET signal is generated (RESET).

Proper operation has been verified at a frequency up to 100

kHz. No abnormal RESET signals will occur with

frequencies lower than 100 kHz and the maximum

Threshold Frequency (96 Hz). An external capacitor

the power on reset (POR) and RESET delay.

The RESET function is activated by any of three

conditions: the watchdog signal moves outside of its preset

limits; the output voltage drops out of regulation by more

than 4.5%; or the IC is in its power up sequence. The RESET

1.0 V.

In conjunction with the Watchdog, the ENABLE

function controls the regulator’s power consumption. The

NCV8141’s output stage and its attendant circuitry are

enabled by setting the ENABLE lead high. The regulator

goes into sleep mode when the ENABLE lead goes low and

the watchdog signal moves outside its preset limit. This

unique combination of control functions in the NCV8141

gives the microprocessor control over its own power down

sequence: i.e. it gives the microprocessor the flexibility to

perform housekeeping functions before it powers down.

VOLTAGE REFERENCE AND OUTPUT CIRCUITRY

Precision Voltage Reference

The regulated output voltage depends on the precision band

gap voltage reference in the IC. By adding an error amplifier

into the feedback loop, the output voltage is maintained within

±4.0% over temperature and supply variation.

Output Stage

The composite PNP−NPN output structure (Figure 7)

provides 500 mA (min) of output current while maintaining

a low drop out voltage (1.25 V) and drawing little quiescent

current (7.0 mA).

Figure 7. Composite Output Stage of the NCV8141

The NPN pass device prevents deep saturation of the

output stage which in turn improves the IC’s efficiency by

preventing excess current from being used and dissipated by

the IC.

Output Stage Protection

The output stage is protected against overvoltage, short

circuit and thermal runaway conditions (Figure 8).

If the input voltage rises above 30 V (e.g. load dump), the

output shuts down. This response protects the internal

circuitry and enables the IC to survive unexpected voltage

transients.