ST AN1743 APPLICATION NOTE

AN1743

APPLICATION NOTE

AUDIO AMPLIFIER SYSTEM USING THE

ANALOG SWITCH STG3699

1. ABSTRACT

This application note is an explanation of the correct use of the STG3699 Analog Switch in mobile
telecom applications.

2. E.S.D. PROTECTION CIRCUITRY DESCRIPTION

The STG Anal og Switch can be used bi-direc tionally (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 V

Figure 1: Generic Circuit for E.S.D. Discharge Protection

Vcc

Input

Output

and two versus GND).

CC

Input

Output

M. Porto

GND

Digital Input IN

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 V

the input to V
The values of the Human Body Model discharge for the STG3699 are very good. In fact the device was

good after a 3KV discharge.

July 2003

, damaging the device or causing incorrect function of the Analog Switch.

CC

is forward biased, so a current will flow from

CC

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AN1743 - APPLICATION NOTE

The following tables show the absolute maximum rating characteristics for the STG3699 device and the
correct signal level applicable to these devices to avoid possible problems.

Table 1: Absolute Maximum Rating

Symbol Parameter Value Units

Vcc Supply Voltage -0.5 to +4.6 V

VI DC Input Voltage -0.5 to Vcc +0.5 V

VIC DC C ontrol Input Voltage -0.5 to +4.6 V

VO DC Output Voltage -0.5 to Vcc +0.5 V

Table 2: Ri ght Level Appl icable in Opera ti ng C onditions

Symbol Parameter Value Units

Vcc Supply Voltage 1.65 to 3.6 V

VI DC Input Voltage

VIC DC Control Input Voltage

≤

Vcc V

≤

Vcc V

VO DC Ou tput Voltage 0 to Vcc V

3. APPLICATION

Usually, in telecom mobile application s, 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 phones.

Figure 2: Audio System Amplifier Schematic

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