The L and X pins of DPA-Switch offer a number of advanced features. The Line Sense (L) pin can be used for overvoltage (OV), under-voltage (UV) lock out, line feed-forward with maximum duty cycle (DCMAX) reduction, remote ON/OFF and synchronization. Connecting the L pin to source will also disable all of these features. The external current limit (X) pin can be used to program a current limit, implement a remote ON/OFF functionality and limit power over line. Connecting the X pin to ground disables all X pin features.
The under-voltage (UV) and overvoltage (OV) shutdown functions can be accessed by the UV/OV form. PI Expert does not support the implementation of remote ON/OFF and synchronization features via the L pin. The L pin has a UV/OV threshold ratio of 2.7. This means that if the UV turn on point is set to 30 VDC, the OV threshold turn off point is automatically set to approximately 81 VDC. PI Expert allows for only the UV point to be specified and calculates the resulting OV threshold for you.
It is possible to implement only UV or only OV using the DPA-Switch but PI Expert does not currently support this. Please see the DPA-Switch data sheet additional information.
External current limit reduction is usually done in high efficiency applications to set the current limit at a point just slightly above the worst-case peak operating current while using a larger device. By increasing the devices size, you reduce the conductions losses. Selecting a devices one or two sizes larger may be beneficial but increasing the device size too much comes at the expensive of increasing the switching losses which may negate the reduction in conduction losses.
You may enter the desired value of KI and PI Expert will display the resulting external current limit and will calculate the necessary value of RLS in Megaohms. Do not select values of KI less than 0.7, or the external current programmed will not be accurate.
Using the X pin you can implement power limiting over line as well. However, PI Expert does not support power limiting over line. Please see the DPA-Switch data sheet for more information.