NCV8675 データシートの表示（PDF） - ON Semiconductor

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NCV8675

350 mA Very Low Iq Low Dropout Linear Regulator with Reset and Reset Delay

ON Semiconductor 

NCV8675

Calculating Power Dissipation

in a Single Output Linear Regulator

The maximum power dissipation for a single output

regulator (Figure 36) is:

PD(max) + [Vin(max) * Vout(min)] Iout(max)

(1)

) VI(max)Iq

where

Vin(max)

Vout(min)

Iout(max)

is the maximum input voltage,

is the minimum output voltage,

is the maximum output current for the

application,

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:

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.

Iin

Vin

Iout

SMART

Vout

REGULATOR®

} Control

Features

Iq

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 is the junction−to−case thermal resistance,

RqCS is the case−to−heatsink thermal resistance,

RqSA is 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.

Thermal, mounting, and heatsinking considerations are

discussed in the ON Semiconductor application note

AN1040/D.

Figure 36. Single Output Regulator with Key

Performance Parameters Labeled

120

100

100

DPAK 1 oz

DPAK 2 oz

10

80

DPAK

D2PAK

60

40 D2PAK 1 oz

D2PAK 2 oz

20

0 100 200 300 400 500 600 700 800 900

COPPER AREA (mm2)

Figure 37. JA vs. Copper Spreader Area

1

0.1

0.000001 0.0001

0.01

Single Pulse

1

100

PULSE TIME (sec)

Figure 38. NCV8675 @ PCB Cu Area 100 mm2

PCB Cu thk 1 oz

http://onsemi.com

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