NCV8664(2006) Ver la hoja de datos (PDF) - ON Semiconductor

Número de pieza

componentes Descripción

Fabricante

NCV8664
(Rev.:2006)

Ultra−Low Iq Low Dropout Linear Regulator

ON Semiconductor 

NCV8664

Circuit Description

The NCV8664 is a precision trimmed 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

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. Over saturation of the output

power device is prevented, and quiescent current in the

ground pin is minimized.

Regulator Stability Considerations

The input capacitor CIN1 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 CIN2. The output or compensation capacitor, COUT

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

capacitor COUT shown in Figure 2 should work for most

applications; however, it is not necessarily the optimized

solution. Stability is guaranteed at values COUT ≥ 10 mF and

an 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:

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

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

+

150oC *

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

6

Share Link: