NCV8506 Series

http://onsemi.com

9

CIRCUIT DESCRIPTION

REGULATOR CONTROL FUNCTIONS

The NCV8506 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.

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

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.

Voltage Adjust

Figure 14 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 14. Adjustable Output

Voltage

NCV8506

15 k

5.1 k

≈5.0 V

1.28 V

APPLICATION NOTES

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 +

[CDELAY(Vdt * Reset Delay Low Voltage)]

Delay Charge Current

Example:

Assume reset Delay Low Voltage = 0.

5.0 V options).

Use the typical value for Delay Charge Current = 4.2

mA.

tDELAY +

[33 nF(1.8 * 0)]

4.2 mA

+ 14 ms

STABILITY CONSIDERATIONS

The output or compensation capacitor helps determine

three main characteristics of a linear regulator: start−up

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

manufacturers data sheet usually provides this information.