SP721APP - 

The SP721 is an array of SCR/Diode bipolar structures for ESD and over-voltage protection to sensitive input circuits. The SP721 has 2 protection SCR/Diode structures per input. There are a total of 6 available inputs that can be used to protect up to 6 external signal or bus lines. Over voltage protection is from the IN (Pins 1-3 and Pins 5-7) to V+ or V-.
The SCR structures are designed for fast triggering at a threshold of one +VBE diode threshold above V+ (Pin 8) or a –VBE diode threshold below V- (Pin 4). From an IN input, a clamp to V+ is activated if a transient pulse causes the input to be increased to a voltage level greater than one VBE above V+. A similar clamp to V- is activated if a negative pulse, one VBE less than V-, is applied to an IN input.