NCV8504 Series

http://onsemi.com

9

CIRCUIT DESCRIPTION

REGULATOR CONTROL FUNCTIONS

The NCV8504 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 4.0% 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.

Adjustable Reset Function

The reset threshold can be made lower by connecting an

lead, as displayed in Figure 14. This lead is grounded to

select the default value of 4.6 V (on the 5.0 V option).

Figure 14. Adjustable RESET

to μP and

System

Power

RESET

DELAY

NCV8504

to μP and

RESET

Port

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 4.0

μA)

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 Comparator

A general use comparator is included whose positive input

terminal is tied to the on−chip bandgap voltage reference.

This provides a very temperature stable referenced

comparator with versatile use in any system. The trip point

can be programmed externally using a resistor divider to the

input monitor (MON) (Figure 15). The typical threshold is

1.29 V on the MON pin.

Figure 15. Flag/Monitor Function

MON

I/O

RESET

μP

FLAG

RESET

GND

DELAY

NCV8504

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 (1.30 V

typical).

Figure 16. Adjustable Output

Voltage

NCV8504

15 k

5.1 k

≈5.0 V

1.28 V