5

Application Diagram

Adj

CS8271

10

mF

Gnd

0.1

mF

ENABLE

)

R1 + R2

R2

(

Step 6:

Test the load transient response by switching in

various loads at several frequencies to simulate its real

work environment. Vary the ESR to reduce ringing.

Step 7:

Remove the unit from the environmental chamber

and heat the IC with a heat gun. Vary the load current as

instructed in step 5 to test for any oscillations.

Once the minimum capacitor value with the maximum

ESR is found, a safety factor should be added to allow for

the tolerance of the capacitor and any variations in regula-

tor performance. Most good quality aluminum electrolytic

capacitors have a tolerance of ±20% so the minimum value

found should be increased by at least 50% to allow for this

tolerance plus the variation which will occur at low tem-

peratures. The ESR of the capacitor should be less than

50% of the maximum allowable ESR found in step 3 above.

Capacitance on the Adjust pin combined with the feed-

back resistors R1 and R2 can affect loop stability and

should also be considered. The CS8271 internal circuitry

produces about 5pF to Ground on the Adjust pin. This

capacitance, plus any additional external capacitance on

the Adjust pin will create a pole when combined with the

resistive feedback network. The effect can be significant

when using large values for the feedback resistors to mini-

mize quiescent current.

A capacitor connected from the Adjust pin to Ground pro-

vides additional means to compensate the regulator by

creating a pole. Alternately, a capacitor can be connected

The maximum power dissipation for a single output regu-

lator (Figure 4) is

(1)

where

tion

Figure 4: Single output regulator with key performance parameters

labeled.

(2)

the package section of the data sheet. Those packages with

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.

Smart

Regulator

Control

Features

}

Calculating Power Dissipation

in a Single Output Linear Regulator

Application Notes: continued