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NCV4264-2

Low IQ Low Dropout Linear Regulator

ON Semiconductor 

NCV4264-2

Circuit Description

The NCV4264-2 is functionally and pin for pin

compatible with NCV4264 with a lower quiescent current

consumption. Its output stage supplies 100 mA with

$2.0% output voltage accuracy.

Maximum dropout voltage is 500 mV at 100 mA load

current. It is internally protected against 45 V input

transients, input supply reversal, output overcurrent faults,

and excess die temperature. No external components are

required to enable these features.

Regulator

The error amplifier compares the reference voltage to a

sample of the output voltage (VOUT) and drives the base of

a PNP series pass transistor by a buffer. The reference is a

bandgap design to give it a temperature-stable output.

Saturation control of the PNP is a function of the load

current and input voltage. Oversaturation of the output

power device is prevented, and quiescent current in the

ground pin is minimized.

Regulator Stability Considerations

The input capacitor CI1 in Figure 2 is necessary for

compensating input line reactance. Possible oscillations

caused by input inductance and input capacitance can be

damped by using a resistor of approximately 1 W in series

with CI2. The output or compensation capacitor, COUT

helps determine three main characteristics of a linear

regulator: startup delay, load transient response and loop

stability. Tantalum, aluminum electrolytic, film, or

ceramic capacitors are all acceptable solutions, however,

attention must be paid to ESR constraints. The capacitor

manufacturer 's data sheet usually provides this

information. The value for the output capacitor COUT

shown in Figure 2 should work for most applications;

however, it is not necessarily the optimized solution.

Stability is guaranteed at values of CQ w 10 mF, with an

ESR v 9 W for the 5.0 V Version, and CQ w 22 mF with

an ESR v 16 W for the 3.3 V Version within the operating

temperature range. Actual limits are shown in a graph in the

Typical Performance Characteristics section.

Calculating Power Dissipation in a Single Output

Linear Regulator

The maximum power dissipation for a single output

regulator (Figure 3) is:

PD(max) + ƪāVIN(max) * VOUT(min)āƫ * IQ(max) ) VI(max) * IQ

(eq. 1)

Where:

VIN(max) is the maximum input voltage,

VOUT(min) is the minimum output voltage,

IQ(max) is the maximum output current for the

application, and IQ is the quiescent current the regulator

consumes at IQ(max). Once the value of PD(max) is known,

the maximum permissible value of RqJA can be calculated:

PqJA

+

(150°C *

PD

TA)

(eq. 2)

The value of RqJA can then be compared with those in the

package section of the data sheet. Those packages with

RqJA's less than the calculated value in Equation 2 will

keep the die temperature below 150°C. In some cases, none

of the packages will be sufficient to dissipate the heat

generated by the IC, and an external heat sink will be

required. The current flow and voltages are shown in the

Measurement Circuit Diagram.

Heat Sinks

A heat sink effectively increases the surface area of the

package to improve the flow of heat away from the IC and

into the surrounding air. Each material in the heat flow path

between the IC and the outside environment will have a

thermal resistance. Like series electrical resistances, these

resistances are summed to determine the value of RqJA:

RqJA + RqJC ) RqCS ) RqSA

(eq. 3)

Where:

RqJC = the junction-to-case thermal resistance,

RqCS = the case-to-heat sink thermal resistance, and

RqSA = the heat sink-to-ambient thermal resistance.

RqJA appears in the package section of the data sheet.

Like RqJA, it too is a function of package type. RqCS and

RqSA are functions of the package type, heat sink and the

interface between them. These values appear in data sheets

of heat sink manufacturers. Thermal, mounting, and heat

sinking are discussed in the ON Semiconductor application

note AN1040/D, available on the ON Semiconductor

Website.

http://onsemi.com

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