ESD Case Sharing ——IPP and earthing

Recently rectified a PC project where the customer had no sound output for the headphones audio port ESD Air 15kV audio decoder and could not automatically recover. The test location is shown in （Figure 1）.

Figure1

The principle is as follows (Figure 2). On the left is the audio decoding chip, the customer connects a 30 ohm magnetic bead in series, the interface uses the varistor of high VC and low IPP value package 0402, and the right is the earphone audio interface.

Figure 2

Hardware PCBA connection such as (Figure 3), the headset seat side of the PCB has 4-layer board and 6-layer board, the purpose is to increase the Gnd layer (increase the ground area).

Figure 3

We tried to replace the varistor with a conventional IPP 8/20μs 8A TVS of BV-FA05ZCD in 4-layer and 6-layer boards, but the problem was not solved. Therefore, we tried to replace the varistor with IPP 35A BV-FA05ZCK TVS in the 6-layer board, and test PASS; On the 4-layer board, change the magnetic bead to 1KΩ@100MHz, and change the varistor to IPP 35A BV-FA05ZCK TVS, and test PASS.

Next, do some simple analysis of ESD static interference, whether the original circuit is 4 or 6 layers, because the varistor IPP value is low, the triggering voltage is more than 300V, so the ESD component too late to respond, and the large energy ESD interference has been conducted along the wire to the decoding IC. Due to the lack of IC inherent immunity, decoding timing and logic errors are caused.

Similarly, although the TVS responds fast enough, the value of IPP is low, the relative internal resistance is large, and the interference energy received by the next IC is also large.