on the right of the box. The 
icon indicates that a custom parameter value has been entered. To restore the default value click the icon again.The PI Device Output OVP form displays the calculated values related to secondary overvoltage protection.
You can turn on using overvoltage protection by selecting YES in Use OVP drop-down box.
The Overvoltage Protection Ratio provides a margin on the Bias Voltage before OVP is triggered. To change Overvoltage Protection Ratio click the calculator icon on the right of the box. The icon indicates that a custom parameter value has been entered. To restore the default value click the icon again.
The VB at OVP field is computed from the Overvoltage Protection Ratio and the maximum value of the Bias voltage across all operating conditions. You can find the maximum Bias Voltage in the RBIAS Circuit Components dialog box.
PI Expert calculates the components set automatically. To replace zener component click the black down arrow control on the right of the calculator icon and select Change. In the Zener dialog box, select the zener you want to add. Click OK. The zener is now replaced. The icon indicates that the custom selected zener is chosen. To restore the default zener click the black down arrow control on the right of the icon and click Default.
For resistor the Change Resistor dialog box opens. In this dialog, click the calculator icon to edit the resistor parameters.