NCV4263−2C

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11

APPLICATIONS INFORMATION

The NCV4263−2C regulator is self−protected with

internal thermal shutdown and internal current limit. Typical

characteristics are shown in Figures 4 to 22.

A ceramic or tantalum 0.1

mF capacitor is recommended

and should be connected close to the NCV4263−2C

package. Higher capacitance and lower ESR will improve

the overall line and load transient response. If extremely fast

input voltage transients are expected then appropriate input

filter is recommended to use in order to decrease rising

and/or falling edges below 50 V/

ms for proper operation.

The filter can be composed of several capacitors in parallel.

The NCV4263−2C is a stable component and requires a

minimum Equivalent Series Resistance (ESR) for the output

capacitor. Stability region of ESR versus Output Current is

shown in Figure 13. The minimum output decoupling value

is 22

mF and can be augmented to fulfill stringent load

transient requirements. Larger values improve noise

rejection and load transient response.

Enable Operation

The Enable pin will turn the regulator on or off. The

threshold limits are covered in the electrical characteristics

table in this data sheet.

Delay Timing

The Delay Timing pin is current source. Current from

Delay Timing pin charges connected capacitor. The value of

this capacitor determines the Reset Delay Time by

Equation 1 and Watchdog Trigger Time by Equation 4.

C

t

RD_des

t

RD

100 nF

(eq. 1)

where:

is capacitance of Delay capacitor

is desired Reset Delay Time

is Reset Delay Time specified in

datasheet

Reset Operation

A reset signal is provided on the Reset Output pin to

provide feedback to the microprocessor of an out of

regulation condition. The timing diagram of reset function

is shown in Figure 21. This is in the form of a logic signal on

Reset Output. Output voltage conditions below the Reset

Threshold causes Reset Output to go low. The Reset Output

Output circuitry is open collector output with internal 30 k

W

pull−up resistor. Leave open this output if the Reset function

is not needed else an external pull−up resistor (5.6 k

W)

Reset Threshold is default set to 93% of nominal Output

range of Output Voltage 70%

resistor output voltage divider, see schematic on Figure 23

and specification of Reset Output.

NCV4263−2C

GND

100 nF

RADJ

RO

WDI

D

I/O

ON

OFF

EN

100 nF

Figure 23. Application Schematic with Adjustable

Reset Threshold

Microprocessor

RESET

5.6 k

W

22

mF

Desired Reset Threshold is given by Equation 2.

V

R

R

RADJ2

V

th(RADJ)

(eq. 2)

where:

is desired Reset Threshold

is Reset Adjust Threshold specified in

datasheet

≤ 50 kW to avoid significant Reset Threshold

error due to RADJ bias current.

Watchdog Operation

Watchdog Input monitors a signal from microprocessor.

This input is positive edge sensitive. The timing diagram of

watchdog function is shown in Figure 22. When watchdog

signal is not received during Watchdog Trigger Time, Reset

Output goes low for a Watchdog Input Low Time and is

periodically generated with period given by Equation 3.

Capacitance of Delay capacitor for setting the desired

Watchdog Trigger Time is given by Equation 4.

t

(eq. 3)

C

t

WTT_des

t

WTT

100 nF

(eq. 4)

where:

is capacitance of Delay capacitor

is desired Watchdog Trigger Time

is Watchdog Trigger Time specified in

datasheet

is Watchdog Input Low Time

is Watchdog Input Period

Thermal Considerations

As power in the NCV4263−2C increases, it might become

necessary to provide some thermal relief. The maximum

power dissipation supported by the device is dependent