SP720 Will Not Clamp Voltage

Hello All,

Currently having an issue where the SP720APP IC will not clamp an analog input voltage to 3.33V.

Here is a schematic of how the circuit is wired. VCC is 3.3V coming from an arduino. The analog inputs are 0-5V and then using a voltage divider a 0-3.3V signal is output. The SP720APP is used to protect the microcontroller analog input pins. The circuit is to be used with a teensy 3.2 where inputs above 3.3 is not allowed. The Arduino is being used to test if the SP720 will work.


I would like to add that the SP720 is clamping to voltage to 4.0V when instead of 3.3V when the analog input is 4.85V.


A snippet from the SP720 datasheet with the relevant portion highlighted is below; the device does not begin conducting until the protected lines rise to one diode drop above the applied Vcc. Figuring 0.6 to 0.7v for a typical diode drop, it would appear that the device is working as designed, according to your description.


A close look at many IC specs will show absolute max values for input pins being given as roughly a diode drop above the supply voltage. It’s common practice to incorporate ESD protection diodes on chip to shunt current flow from excess voltage into the supply or ground rail, depending on polarity. Application of a voltage from a source capable of delivering significant current can, as a result, do bad things. That 1K resistance shown in the divider will go far towards limiting any damage from minor over-voltages and probably even minor ESD events, even without the SP720.