NCV4275A 查看數據表（PDF） - ON Semiconductor

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NCV4275A

5.0 V, 3.3 V 450 mA Low-Dropout Voltage Regulator with Reset

ON Semiconductor 

NCV4275A

Calculating Power Dissipation

in a Single Output Linear Regulator

The maximum power dissipation for a single output

regulator (Figure 25) is:

PD(max) + [VI(max) * VQ(min)] IQ(max)

(1)

) VI(max)Iq

where

VI(max)

VQ(min)

IQ(max)

Iq

is the maximum input voltage,

is the minimum output voltage,

is the maximum output current for the

application,

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.

II

IQ

VI

SMART

VQ

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

RqCS

RqSA

is the junction−to−case thermal resistance,

is the case−to−heatsink thermal resistance,

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 25. Single Output Regulator with Key

Performance Parameters Labeled

http://onsemi.com

11

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