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The next example is headset, whether its wired or a Bluetooth wireless headset, the protection content is relatively similar. Audio ports and speaker outputs are prone to ESD damage as history has shown whether it is in a headset or a smart phone. ESD protection is needed in either case. In the illustration on the right, the topology shows an audio amplifier having dual power rails, one achieved by using a charge pump to create the negative rail. This will result in a bipolar amplifier output which will require a bidirectional ESD diode. Ideally, the ESD diode should be placed directly at the interface where the ESD event can come in. Whether it is in front of the EMI filter (ferrite bead) or behind it, it will depend on the application and EMI requirements. The electrical requirements for selecting the appropriate ESD diode will be mostly based on the working voltage. Most audio amplifiers are below 5 V, therefore a 5.3 V bidirectional ESD diode would be optimal in this case. Similar with the keypad application, speed is not critical as audio range is only up to 22 kHz. Line capacitances over 5 pF would be fine. Because the audio amplifiers are traditionally very sensitive to ESD events, and especially with the newer Class D amplifiers, it is important to select a ESD diode with very low dynamic resistance and therefore, low clamping voltage. The ESD diodes shown on the bottom right are typical ESD diodes that are optimal for audio headset/speaker protection.
