No output when 2k pull-down resistor is added

Hi, Vio,

When performing this test, do you have an LC filter populated? I will check for the reason of this behavior and will get back to you as soon as possible.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Yes, LC filter is populated. I can get the same phenomenon on the TAS5733L EVM.
I have tested several other amplifiers with the same configuration. Only TAS5733L can't work. Others such as TPA3110, TAS5707 and TAS5711 is still working even if i put the 2k ohm resistor to the ground.

Thanks.
Best regards,
Vio Liu

Hi Diego,

Any progress? My customer is eager to know the reason. Thanks.

Best regards,
Vio Liu

Hi, Vio,

Getting the root cause of this might take some time as this kind of testing is not typical. I think this behavior is related to the fact that the power stage of the TAS5733L is different to other Class D amplifiers as it is optimized to have a better efficiency with low power operation. 

Have you monitored the error report register (0x02) to identify if the amplifier is reporting any error?. If the PWM is stopped, that means the amplifier put  the output in high impedance state. This is part of the amplifier's protection system.

Best Regards,

  -Diego Meléndez López  
   Audio Applications Engineer

Hi Diego,

Thanks for your comments. I guess it is because of the DC protection. But the datasheet don't mentioned anything about DC protection. I've monitored the error register. It shows nothing different.
If you have any progress, please let me know. Thanks.

Best regards,
Vio Liu

Hi Diego,

Do you have any progress on this test? My customer is eager to know the reason. Thanks.

Best regards,
Vio Liu

Hi, Vio,

Sorry for the delay, I am working with the team to find the root cause of this. Can you please let us know the reason of adding the 2k pull-down resistors to the outputs?.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

My customer is using this circuit in their audio amplifier board automatic test system. They would like to acquire the output voltage of audio amplifiers with ADC, but they need to attenuate the signal with resistor divider at first.

Thanks for your support!

Best regards,
Vio Liu

Hi, Vio,

Thanks for the additional information. I will pass this information to the team and will get back to you as soon as I get any update. 

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Thanks for your help!

Best regards,
Vio Liu

Hi, Vio,

Can you please share the LC filter values and power supply used while performing the test in the system?. 

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

It will happen on our EVM. I think you can help test with the parameters of EVM. It's China holiday now, I'am out and I can tell you the parameters later after vacation.

Thanks.
Best regards,
Vio Liu

Hi Diego,

Do you have any update on this case? Thanks.

Best regards,

Vio Liu

Hi Diego,

Any update for this case? Thanks.

Best regards,
Vio Liu

Hi Diego,

Any update for this case? Thanks.

Best regards,
Vio Liu

Hi, Vio,

Sorry for the delay, I have not received an update yet, I will contact you once I get any information.

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Thanks. My customer keeps asking me every 2 or 3 days. If you can help push it would be better.

Best regards,
Vio Liu

Hi, Vio,

Sorry for the delay, I have some updates. The difference between the TAS5733L and the older amplifiers is that the '33L has an integrated feature that performs a test during power up to verify that the outputs of the amplifier are not shorted or loaded down to ground. This protection feature is added to prevent any damage to the output stage caused by a short. As this feature performs the test during startup, can you please suggest your customer to connect the amplifier boards to their test system after powering up the amp?. 

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer

Hi Diego,

Could you please tell me more details? For example, if 2k resistor to ground is regarded as short, what about 20k resistor? What's the criteria of the current? Thanks.

Best regards,
Vio Liu

Hi, Vio,

If a larger Impedance is used, probably the amplifier will not trigger the protection circuit. Do you know if your customer tried testing the boards as I suggested? (first powering up the amplifiers then connect to the test system).

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer