NCV8664

http://onsemi.com

9

Circuit Description

The NCV8664 is a precision trimmed 3.3 V and 5.0 V

fixed output regulator. Careful management of light load

consumption combined with a low leakage process results

in a typical quiescent current of 22

mA. The device has

current capability of 150 mA, with 600 mV of dropout

voltage at full rated load current. The regulation is provided

by a PNP pass transistor controlled by an error amplifier

with a bandgap reference. The regulator is protected by

both current limit and short circuit protection. Thermal

shutdown occurs above 150°C to protect the IC during

overloads and extreme ambient temperatures.

Regulator

The error amplifier compares the reference voltage to a

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. Over saturation of the output

power device is prevented, and quiescent current in the

ground pin is minimized.

Regulator Stability Considerations

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

helps determine three main characteristics of a linear

regulator: startup delay, load transient response and loop

stability. The capacitor value and type should be based on

cost, availability, size and temperature constraints.

Tantalum, aluminum electrolytic, film, or ceramic

capacitors are all acceptable solutions, however, attention

must be paid to ESR constraints. 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 manufacturer’s data sheet

usually provides this information. The value for the output

applications; however, it is not necessarily the optimized

ESR ≤ 9

W 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:

IQ(max) ) VI(max) @ Iq

(eq. 1)

PD(max) + [VIN(max) * VOUT(min)] @

Where:

PqJA +

PD

(eq. 2)

package section of the data sheet. Those packages with

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

RqJA + RqJC ) RqCS ) RqSA

(eq. 3)

Where:

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.