During the AC diagnostic process, particularly in environments like automotive production lines, poor contact in the loudspeaker connectors or improper wire harness crimping will cause deviations in AC diagnostics. The reason is that AC diagnostics performs 32 or 64-point sampling on the external impedance. Such unstable connections introduce additional contact resistance, which is captured across the 64 samples and incorporated during the averaging calculation. For a precision chip like the TAS6424E-Q1 that calculates impedance by sensing minute current signals, this can lead to significantly larger readback AC impedance values.

Using the TAS6424E-Q1 EVM development board for simulation testing, the 4.0ohm standard load connector was rapidly plugged and unplugged manually while initiating AC diagnostics. By artificially creating unstable instantaneous contact resistance to interfere with the chip's 32/64-point current sampling, the abnormal result where the readback impedance was much higher than the nominal 4.0ohm was successfully reproduced, verifying the direct impact of poor connections on the accuracy of precision AC diagnostics.

Figure 3-1 shows the test method; for a normal 4.0ohm resistor as Figure 3-2, Channel 1 can measure an impedance of 4.2ohm; when Figure 3-3 is open circuit, Channel 1 will read an impedance greater than 70.0ohm;

Figure 3-4 shows the results obtained when rapidly plugging and unplugging the Channel 1 connector during testing. It can be seen that Channel 1 originally read 4.0ohm, but during rapid plugging and unplugging, the impedance reached 14.0ohm. Different plug/unplug frequencies have a probability of yielding different values, but the AC diagnostic results are all greater than the actually measured impedance value.

It should be noted that this is not a defect of the chip; rather, it is precisely because of AC diagnostics that developers are able to identify issues such as poor connector contact.