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CS8371

8.0 V/1.0 A, 5.0 V/250 mA Dual Regulator with Independent Output Enables and NOCAP
™

ON Semiconductor 

CS8371

cause small signal oscillations at the output. This will

depend on the load conditions. With these types of loads, a

traditional output stage may be better suited for proper

operation.

Output 1 employs NOCAP. Refer to the plots in the

Typical Performance Characteristics section for

appropriate output capacitor selections for stability if an

external capacitor is required by the switching

characteristics of the load. Output 2 has a Darlington

NPN−type output structure and is inherently stable with any

type of capacitive load or no capacitor at all.

Calculating Power Dissipation in a

Dual Output Linear Regulator

The maximum power dissipation for a dual output

regulator (Figure 24) is

PD(max) + NJVIN(max) * VOUT1(min)NjIOUT1(max) )

NJVIN(max) * VOUT2(min)NjIOUT2(max) ) VIN(max)IQ (1)

where:

VIN(max) is the maximum input voltage,

VOUT1(min) is the minimum output voltage from VOUT1,

VOUT2(min) is the minimum output voltage from VOUT2,

IOUT1(max) is the maximum output current, for the

application,

IOUT2(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 RΘJA can be calculated:

RQJA

+

150°C *

PD

TA

(2)

The value of RΘJA can be compared with those in the

package section of the data sheet. Those packages with

RΘJA’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

SMART

REGULATOR

IOUT1

VOUT1

Control

Features

IOUT2

VOUT2

IQ

Figure 24. Dual Output Regulator With Key

Performance Parameters Labeled.

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 RΘJA:

RQJA + RQJC ) RQCS ) RQSA

(3)

where:

RΘJC = the junction−to−case thermal resistance,

RΘCS = the case−to−heatsink thermal resistance, and

RΘSA = the heatsink−to−ambient thermal resistance.

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

RΘJA, it too is a function of package type. RΘCS and RΘSA

are functions of the package type, heatsink and the interface

between them. These values appear in heat sink data sheets

of heat sink manufacturers.

PACKAGE THERMAL DATA

RΘJC

RΘJA

Parameter

Typical

Typical

TO−220

SEVEN LEAD

2.4

50

Unit

°C/W

°C/W

http://onsemi.com

148

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