TAD5242: A question about the TAD5242 audio DAC.

jeremy savonet

Prodigy 10 points

Part Number: TAD5242

Tool/software:

Hi support team,

We have a question regarding TAD5242 audio DAC.

The MD5/MD4 = 0b11 mode looks dedicated and optimized for headphones load.

The following connection scheme (figure 6-10) from the datasheet is recommended.

The common mode voltage of the stereo output is connected to OUT1M and OUT2M.

The most widely adopted common mode voltage is 0 volts, by connecting these pins to the ground plane, thus, having OUT1P and OUT2P swing alternatively positive and negative in value around this common mode. The swing amplitude is 1Vrms.

Could you confirm that, although violating the -0.3V absolume maximum rating, both OUT1P and OUT2P pins will output proper unclipped negative signals when the common mode is set to 0 ?

Kind regards,
Jeremy

2 months ago

0 Lakshmi Narasimhan Badrinarayanan 2 months ago

TI__Expert 7760 points

Hi Jeremy,

The common mode voltage is generated by the device on the OUT1M pin, and it is a non-zero voltage.

It is sensed back by the OUT2M pin of the device.

The swing on the OUT1P/OUT2P will always be above 0V in this configuration.

Thanks and Regards,

Lakshmi Narasimhan

0 Arash Loloee 2 months ago

TI__Mastermind 30711 points

Hello Jeremy,

The common mode voltage is internally generated . Pseudo-differential connection for one channel is shown below.

Regards,

Arash

0 jeremy savonet 2 months ago

Prodigy 10 points

Hi all,

Thanks for those quick answers.

In the event of the OUT1M pin being shorted to ground via (for example) the output minijack connector, how will the DAC handle this ? The common mode will drop to zero. Will the DAC survive ? If not, do you have any in-between recommended circuit for headphones output in "risky" environment as far as common mode is concerned ?

Thanks!

0 Arash Loloee 2 months ago in reply to jeremy savonet

TI__Mastermind 30711 points

Hello Jeremy,

Even if there is an accidental short on its output , it should not get damaged.

Kind Regards,

Arash

0 jeremy savonet 2 months ago in reply to Arash Loloee

Prodigy 10 points

Hello,

Thank you again for your reply.

We wanted to be sure they won't be an issue with our design so :

- okay but what if the output is permanently shorted ? that may really happen because this is the ground signal and ground is supposed to be at 0V.

- any in between circuit recommendation please ?

Kind regards,
Jeremy

+1 Arash Loloee 2 months ago in reply to jeremy savonet

TI__Mastermind 30711 points

Hello,

The DAC has short circuit protection and in the case of any short circuit even, it will shut down and there will be no damage to the IC. Once the short is removed, It has to reset/powered up again.

Regards,

Arash

0 jeremy savonet 2 months ago in reply to Arash Loloee

Prodigy 10 points

Hello,

Thank you for your help and helping clarify this case.

Would be great if the datasheet could be updated to explicitely state that ;)

Have a great day all,
Regards

Jeremy

0 jeremy savonet 2 months ago

Prodigy 10 points

HI all,

On last question regarding this topic.

In the MD45 = 0b11 mode, this is the typical connection. What is the suggested value for the resistor R please ? This is not indicated in the datasheet.

As this mode is for headphones only, is this resistor mandatory and what happens on a connector where the headphones set can be randomly plugged and removed ?

Thank you

Jeremy

0 Arash Loloee 2 months ago in reply to jeremy savonet

TI__Mastermind 30711 points

Hello, In headphone mode the range of acceptable load is from 8 Ohm to 300 Ohm with 16 Ohm being nominal. If headphone is removed, then there is nothing there to be driven at those pins.

Regards,

Arash

0 jeremy savonet 1 month ago in reply to Arash Loloee

Prodigy 10 points

Hello,

Noted. It does not answer our question but anyways we have put some protection resistors in our design in case of.

Regards,
Jeremy

0 Arash Loloee 1 month ago in reply to jeremy savonet

TI__Mastermind 30711 points

Seems you externally did reinforcement as well. Should be okay.

Regards,

Arash

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TAD5242: A question about the TAD5242 audio DAC.