NCV8184 데이터 시트보기 (PDF) - ON Semiconductor

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NCV8184

Tracking Regulator/Line Driver - Micropower, Low Dropout 70 mA

ON Semiconductor 

NCV8184

External Capacitors

The output capacitor for the NCV8184 is required for

stability. Without it, the regulator output will oscillate.

Actual size and type may vary depending upon the

application load and temperature range. Capacitor effective

series resistance (ESR) is also a factor in the IC stability.

Worst−case is determined at the minimum ambient

temperature and maximum load expected.

The output capacitor can be increased in size to any

desired value above the minimum. One possible purpose of

this would be to maintain the output voltage during brief

conditions of negative input transients that might be

characteristic of a particular system.

The capacitor must also be rated at all ambient

temperatures expected in the system. To maintain regulator

stability down to −40°C, a capacitor rated at that temperature

must be used.

More information on capacitor selection for SMART

REGULATOR®s is available in the SMART REGULATOR

application note, “Compensation for Linear Regulators,”

document number SR003AN/D, available through our

website at http://www.onsemi.com.

Calculating Power Dissipation in a Single Output

Linear Regulator

The maximum power dissipation for a single output

regulator (Figure 23) is:

PD(max) + {VIN(max) * VOUT(min)} IOUT(max)

) VIN(max)IQ

(eq. 1)

where:

VIN(max) is the maximum input voltage,

VOUT(min) is the minimum output voltage,

IOUT(max) is the maximum output current, for the

application,and

IQ is the quiescent current the regulator consumes at

IOUT(max).

Once the value of PD(max) is known, the maximum

permissible value of RqJA can be calculated:

RqJA

+

150°

C*

PD

TA

(eq. 2)

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

Package Thermal Data 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.

IIN

VIN

SMART

REGULATOR®

Control

Features

IOUT

VOUT

IQ

Figure 23. Single Output Regulator with Key

Performance Parameters Labeled

Heatsinks

A heatsink 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−heatsink thermal resistance, and

RqSA = the heatsink−to−ambient thermal resistance.

RqJC appears in the package section of the data sheet. Like

RqJA, it is a function of package type. RqCS and RqSA are

functions of the package type, heatsink and the interface

between them. These values appear in heat sink data sheets

of heatsink manufacturers.

http://onsemi.com

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