Hi,
We are using the TAS5611A in a configuration where there is a transformer at the end of the smoothing filter. The op smoothing filter is more or less the same as that of the EVM circuit of this device. We have built several boards and are testing them. We noticed that there are differences in the no load current (no load on the transformer secondary) between the boards. On a good device the no load current is about 150mA on a compromised device the no load current can be as high as 500mA. We think that on the devices showing high no load current the heat sink might not have been seated properly. The transformer magnetization current is negligible.
Then when tested with a load the good devices give an output acoustic power that is in line with expectations of the circuit and the compromised devices give an output that is much less. We are fairly positive that even though the heat sink might not have been seated properly the devices did not overheat excessively. We would also expect that even if the devices did overheat as there is protection on the circuit the device should not be damaged.
The testing however points to permanent damage on the compromised power amplifiers and I suspect that the Rds-on in the internal mosfets have increased which explains the higher no load current as well as the reduced acoustic output.
The questions are as follows:
1. Even if the devices did overheat is it possible for the MOSFETS to be compromised and the Rds-on to increase?
2. Wouldn't the temperature protection of the IC prevent permanent damage such as this?
3. With temperature rise does the Rds-on migrate to a higher value and stay there?
4. Another possibility is that there could be a large current drawn by the transformer in the first cycle depending on which part of the waveform cycle it is switched in. Wouldn't the short circuit protection safeguard the chip against damage from short circuits?
I look forward to answers and discussion to the above.
BR
Manjula
