This application note is an explanation of the correct use of the STG3699 Analog Switch in mobile telecom applications.
E.S.D. PROTECTION CIRCUITRY DESCRIPTION
The STG Analog Switch can be used bi-directionally (one input/two outputs or two inputs/one output) depending on the application. Both inputs and outputs are protected from the E.S.D. discharge by a circuit that can be synthesized as four protection diodes (two versus VCC and two versus GND).
To correctly use these devices it is very important to consider the presence of the protection diodes. For example, a possible problem area is applying a wrong input level signal (input level higher than power supply). In fact, in this condition the diode versus VCC is forward biased, so a current will flow from the input to VCC, damaging the device or causing incorrect function of the Analog Switch.
The values of the Human Body Model discharge for the STG3699 are very good. In fact the device was good after a 3KV discharge.
Usually, in telecom mobile applications, an Audio Amplifier drives the Analog Switch. So the designer must consider different parameters to realize a PCB without problems.
A channel-to-channel Cross Talk or a drift of a few parameters are typical problems of bad coupling between the Audio Amplifier and the Analog Switch.
The following schematic shows a typical speaker amplifier system for telecom mobile p