NCV8184

http://onsemi.com

8

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:

application,and

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

R

qJA +

150

°C * TA

PD

(eq. 2)

Package Thermal Data Section of the data sheet. Those

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.

Figure 23. Single Output Regulator with Key

Performance Parameters Labeled

SMART

Control

Features

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

R

qJA + RqJC ) RqCS ) RqSA

(eq. 3)

where:

functions of the package type, heatsink and the interface

between them. These values appear in heat sink data sheets

of heatsink manufacturers.