Rev C

APPLICATION NOTES

WALL INDUSTRIES, INC.

SP & SPW SERIES

(888) 597-WALL

www.wallindustries.com

4 of 7

Output Voltage Trim

The following information is provided to allow quick calculation of the trim resistor value for a desired output voltage. The general

procedure for calculating a trim resistor is as follows:

1.

Determine the desired output voltage (Vo)

2.

Select Equation. (Trim Low/Trim High)

3.

Use the data in Table 1 to complete the equation.

4.

Evaluate.

In order to trim low use Equation 1 and Table 1 to calculate resistor RTL for the desired output voltage.

Vo - Desired output voltage.

All resistor values in K ohms.

In order to trim high use Equation 2 and Table 1 to calculate resistor RTH for the desired output voltage.

Vo - Desired output voltage.

All resistor values in K ohms.

MODEL

(Output Voltage)

(K OHMS)

(K OHMS)

(K OHMS)

(VOLTS)

3.3V

0.750

0.499

2.32

2.495

5.0V

2.49

10.0

2.49

2.495

8.0V

5.49

10.0

2.49

2.495

9.0V

6.49

10.0

2.49

2.495

12.0V

9.53

13.7

2.49

2.495

15.0V

12.4

13.7

2.49

2.495

24.0V

21.5

15.4

2.49

2.495

26.0V

17.6

15.4

1.87

2.495

32.0V

23.7

12.7

2.00

2.495

Table 1 : Trim Low/High Data Table.

Note: Output trim +/- 10% max.

Schematic 1: Trim Low

Equation 1: Trim Low

LIM

REF

o

R

R

V

REF

o

L

R

V

V

V

V

RT

H

L

REF

))

(

(

)

(

1

Schematic 2: Trim High

Equation 2: Trim High

RT

V

R

H

REF

VV

R

V

R

LIM

oREF

H

REF

L