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NCP694

1A CMOS Low-Dropout Voltage Regulator

ON Semiconductor 

NCP694

APPLICATIONS INFORMATION

A typical application circuit for the NCP694 series is

shown in Figure 5, Typical Application Schematic.

Input Decoupling (C1)

A 4.7 mF capacitor either ceramic or tantalum is

recommended and should be connected as close as possible

to the pins of NCP694 device. Higher values and lower ESR

will improve the overall line transient response.

Output Decoupling (C2)

The minimum decoupling value is 4.7 mF and can be

augmented to fulfill stringent load transient requirements.

The regulator accepts ceramic chip capacitors as well as

tantalum devices. If a tantalum capacitor is used, and its ESR

is large, the loop oscillation may result. Because of this,

select C2 carefully considering its frequency characteristics.

Larger values improve noise rejection and load regulation

transient response.

Enable Operation

The enable pin CE will turn on or off the regulator. These

limits of threshold are covered in the electrical specification

section of this data sheet. If the enable is not used then the

pin should be connected to Vin. The D version devices

(NCP694DxxxxT1G) have additional circuitry in order to

reach the turn−off speed faster than normal type. When the

mode is into standby with CE signal, auto discharge

transistor turns on.

Hints

Please be sure the Vin and GND lines are sufficiently wide.

If their impedance is high, noise pickup or unstable

operation may result.

Set external components, especially the output capacitor,

as close as possible to the circuit, and make leads as short as

possible.

Thermal

As power across the NCP694 increases, it might become

necessary to provide some thermal relief. The maximum

power dissipation supported by the device is dependent

upon board design and layout. Mounting pad configuration

on the PCB, the board material, and also the ambient

temperature effect the rate of temperature rise for the part.

This is stating that when the NCP694 has good thermal

conductivity through the PCB, the junction temperature will

be relatively low with high power dissipation applications.

Output Voltage Setting of Adjustable Version.

An external two resistors are required for setting desired

output voltage as shows Figure 3. Output Voltage Setting.

The equation for the output voltage is mentioned in equation

below.

Vout + Vref ) R1 @ I1

ǒ Ǔ + Vref ) R1 @ Iadj ) I2

ǒ Ǔ + Vref ) R1 @ VrefńRadj ) R1 @ ǒVrefńR2Ǔ

ǒ Ǔ ǒ Ǔ + Vref @ 1 ) R1ńRadj ) ǒR1ńR2Ǔ

(eq. 1)

ǒ Ǔ ǒ Ǔ + 1.0 @ 1 ) R1ńRadj ) ǒR1ńR2Ǔ

For better accuracy, choosing R2 << Radj reduces the error

given by ADJ pin consumption. The typical resistance Radj

is showed in Figure 4. ADJ Pin Resistance

Vout

1.8

R1

I1

1.6

ADJ

Vref = 1 V

1.4

Iadj

Radj

GND

R2

I2

1.2

1.0

Figure 3. Output Voltage Setting

0.8

−50 −25

0

25

50

75

100

TJ, TEMPERATURE (°C)

Figure 4. ADJ Pin Resistance vs. Temperature

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