Both TOPSwitch-HX and TOPSwitch-GX have a number of features available depending on the family and package chosen.
The voltage monitor (V) pin can be used to implement a large number of features including DCMAX reduction over line, remote On/Off, hysteric and latching overvoltage protection (OVP). The V pin is only available on eSIP, M and Y package TOPSwitch-HX family of devices. V pin functions can also be implemented using the M pin found on other packages.
PI Expert currently supports line under-voltage (UV) and overvoltage (OV) functions. You can choose to implement both UV and OV using a single resistor, rated for the voltage seen across this resistor, with a locked UV/OV ratio of approximately 4. This means choosing a UV on threshold of 100 VDC automatically results in an OV off threshold of approximately 400 VDC. PI Expert is also able to implement UV and OV separately.
The line sense (L) pin available on F, R and Y packaged TOPSwitch-GX devices is similar to the V pin found on some TOPSwitch-HX devices. The L pin however lacks some of the more advanced features such as OVP and dual-slope DCMAX reduction. The line feed-forward with DCMAX reduction features in TOPSwitch-HX provides superior line frequency ripple rejection when compared to the TOPSwitch-GX family. PI Expert supports OV and UV together or separately on the L pin.
Although the V and L pin are similar in their function their actual ratings and underlying operation are different. Please see the appropriate data sheet for more information.
The external current limit (X) pin is found on both TOPSwitch-GX and TOPSwitch-HX devices. For TOPSwitch-GX the X pin is available on the F,R and Y packages while TOPSwitch-HX devices the X pin is available on the M, Y and eSIP packages. The X pin not only allows for external current limit programming, but it can also be used for remote On/Off, synchronization, and power limiting over line. PI Expert supports external current limiting (KI limiting) and overload power limiting over line.
KI limiting is useful in situations where a larger than necessary device has been chosen to reduce the conduction losses. It is recommended that the KI value is not set to a level significantly below 0.7 for both TOPSwitch-HX and TOPSwitch-GX. Increasing the device size more than two devices larger will usually result in increased switching losses. These will likely increase to the point where any benefit from the reduced conduction losses is lost. Besides, the accuracy of the external current limit decreases as the KI is reduced.
PI Expert supports the design of overload power limiting automatically. Power limiting over line is a valuable feature because as the line voltage increases the power that is able to be delivered to the load will also increase. This often times is undesirable. Power limiting is available as long as the value of the overload power resistor, RPL, is reasonable. The necessary value of RPL can become so large (greater than 20 MΩ), especially on TOPSwitch-HX designs as to make the implementation of overload power limiting impractical. Thus output overload power limiting might not always be required, and, in such cases, simple current limiting over line should be sufficient for limiting overload power.
The multifunction (M) pin is found on both TOPSwitch-GX and TOPSwitch-HX devices on the P and G packages. The M pin can be used as either an X pin or a V/L pin; however, it can only serve the function of one of these pins at a time. This means that if you want to use X pin features and L/V pin features at the same time, you cannot use a P or G package part. PI Expert supports all features that are supported using the L/V and X pin using the M pin. The user interface enforces the usage rules given above making design with the M pin easier.
Generalizations have been made while describing the various possible combinations of device family, package choice, and feature usage possible. PI Expert makes all of the necessary calculations and provides guidance through its user interface to make utilization of these features as easy and accurate as possible. Please refer to product data sheets for more detailed explanations of product features.