NCV8501 Series

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10

CIRCUIT DESCRIPTION

REGULATOR CONTROL FUNCTIONS

The NCV8501 contains the microprocessor compatible

control function RESET (Figure 13).

Figure 13. Reset and Delay Circuit Wave Forms

RESET

DELAY

Threshold

DELAY

Threshold

RESET

RESET Function

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

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

as 1.0 V.

ENABLE Function

pin is held low. The part has an internal pull down if the pin

is left floating. This is intended for failure modes only. An

external connection (active pulldown, resistor, or switch) for

normal operation is recommended.

The integrity of the ENABLE pin allows it to be tied

directly to the battery line through an external resistor. It will

withstand load dump potentials in this configuration.

Figure 14. ENABLE Function

GND

NCV8501

ENABLE

10 k

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 15). The typical

threshold is 1.20 V on the MON pin.

Figure 15. FLAG/Monitor Function

MON

I/O

RESET

mP

FLAG

RESET

GND

DELAY

NCV8501

Voltage Adjust

Figure 16 shows the device setup for a user configurable

a voltage divider referenced to the output voltage. The loop

is balanced around the Unity Gain threshold (1.28 V

typical).

Figure 16. Adjustable Output Voltage

NCV8501

15 k

5.1 k

≈5.0 V

1.28 V