portant when analyzing closed loop stability. The minimum

and maximum room temperature values of this resistor are

specified in the Electrical Characteristics section of this data

sheet, and a curve showing the temperature coefficient is

shown in the curves section. Minimum values of R

lower phase margins.

Test Circuit

The test circuit shown in

Figure 2 can be used to measure

and verify various LM3420 parameters. Test conditions are

set by forcing the appropriate voltage at the V

point and selecting the appropriate R

the Electrical Characteristics section. Use a DVM at the

“measure” test points to read the data.

V

The regulation voltage (V

nally trimmed by adding a single resistor from the COMP pin

to the +IN pin or from the COMP pin to the GND pin, depend-

ing on the desired trim direction. Trim adjustments up to

the temperature coefficient. (See temperature coefficient

curve shown in

Figure 3 below.)

Formulas for selecting trim resistor values are shown below,

based on the percent of increase (%incr) or percent of de-

crease (%decr) of the output voltage from the nominal volt-

age.

For LM3420-4.2

R

R

For LM3420-8.2

DS012359-7

FIGURE 2. LM3420 Test Circuit

DS012359-8

Normalized Temperature Drift with

Output Externally Trimmed

DS012359-9

Increasing V

REG

DS012359-10

Decreasing V

REG

FIGURE 4. Changing V

REG

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