APPLICATION NOTES SP/SPW Series Trim Function 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. 2. 3. 4. Determine the desired output voltage (Vo) Select Equation. (Trim Low/Trim High) Use the data in Table 1 to complete the equation. Evaluate. In order to trim low use Equation 1 and Table 1 to calculate resistor RTL for the desired output voltage. Equation 1: Trim Low Vo VREF RTL V RLIM 1 REF ( RL ) ( RH (Vo VREF )) Vo - Desired output voltage. All resistor values in K ohms. Schematic 1: Trim Low In order to trim high use Equation 2 and Table 1 to calculate resistor RTH for the desired output voltage. Equation 2: Trim High RTH VREF Vo VREF RH VREF RL R LIM Vo - Desired output voltage. All resistor values in K ohms. Schematic 2: Trim High MODEL (Output Voltage) RH RLIM RL VREF (K OHMS) (K OHMS) (K OHMS) (VOLTS) 3.3V 5.0V 8.0V 9.0V 12.0V 15.0V 24.0V 26.0V 32.0V 0.750 2.49 5.49 6.49 9.53 12.4 21.5 17.6 23.7 0.499 10.0 10.0 10.0 13.7 13.7 15.4 15.4 12.7 2.32 2.49 2.49 2.49 2.49 2.49 2.49 1.87 2.00 2.495 2.495 2.495 2.495 2.495 2.495 2.495 2.495 2.495 Table 1 : Trim Low/High Data Table. Note: Output trim +/- 10% max. Wall Industries, Inc. 5 Watson Brook Road Exeter, NH 03833 603-778-2300 www.wallindustries.com Fax 603-778-9797