NCV8508(2004) 데이터 시트보기 (PDF) - ON Semiconductor

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NCV8508
(Rev.:2004)

5.0 V, 250 mA LDO with Watchdog and RESET

ON Semiconductor 

NCV8508

APPLICATION NOTES

Calculating Power Dissipation in a Single Output

Linear Regulator

The maximum power dissipation for a single output

regulator (Figure 19) is:

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

(1)

) VIN(max)IQ

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).

IIN

VIN

SMART

REGULATOR®

IOUT

VOUT

100

90

80

70

60

50

40

0

0.5

1.0

1.5

2.0

2.5 3.0

Copper Area (inch2)

Figure 20. 16 Lead SOW (4 Leads Fused), qJA as

a Function of the Pad Copper Area (2 oz. Cu

Thickness), Board Material = 0.0625, G−10/R−4

} Control

Features

IQ

Figure 19. Single Output Regulator with Key

Performance Parameters Labeled

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

permissible value of RqJA can be calculated:

RqJA

+

150°C *

PD

TA

(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

heatsink will be required.

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

(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 too 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 heatsink data sheets

of heatsink manufacturers.

ORDERING INFORMATION

Device

Output Voltage

Package

Shipping†

NCV8508DW50

5.0 V

SO−16L

47 Units / Rail

NCV8508DW50G

5.0 V

SO−16L

(Pb−Free)

47 Units / Rail

NCV8508DW50R2

5.0 V

SO−16L

1000 / Tape & Reel

NCV8508D2T50

5.0 V

D2PAK−7

50 Units / Rail

NCV8508D2T50G

5.0 V

D2PAK−7

(Pb−Free)

50 Units / Rail

NCV8508D2T50R4

5.0 V

D2PAK−7

750 / Tape & Reel

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging

Specifications Brochure, BRD8011/D.

http://onsemi.com

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