Inconsistent Dynamic Range on PCM1798

Stephen Flower

Other Parts Discussed in Thread: PCM1798

Hi,

I'm currently struggling with an issue with PCM1798s whereby on some of our prototype units the we get a dynamic range of 114dB unweighed, while others give 110dB. Upon reconfiguring the clocks for an alternative sample rate the units that were previously giving 114dB now give 110dB.

I have spent a lot of time working on reset, clock and format timing, but all to no avail. If anyone else has experienced this problem, or have any pointers as to where we may be missing something that would be great.

Thanks,

Steve

over 11 years ago

0 Don Dapkus over 11 years ago

TI__Guru**** 189399 points

Hi, Steve,

Welcome to e2e, and I am sorry that you are having difficulties with our device.

If you cycle the power, does the DR go back to 114 dB?

-d2

0 Stephen Flower over 11 years ago in reply to Don Dapkus

Prodigy 40 points

Hi there,

Yes it does return to 114dB after a power cycle.

All the best,

Steve

0 Stephen Flower over 10 years ago in reply to Stephen Flower

Prodigy 40 points

I'm still not having much luck with this, so here are some timing diagrams of our system in case it shows up any potential issues.

0 Don Dapkus over 10 years ago in reply to Stephen Flower

TI__Guru**** 189399 points

Hi, Stephen,

Unfortunately, when doing this, you have to power cycle the IC to get the fully 114 dB of performance.

-d2

0 Stephen Flower over 10 years ago in reply to Don Dapkus

Prodigy 40 points

Hi d2,

Thanks for the response, do both Vdd and Vcc need to be cycled? Any particular order? and is the timing of the reset line critical at all?

All the best,

Steve

0 Brian Wang over 10 years ago in reply to Stephen Flower

TI__Expert 7855 points

Hi Steve,

Both power supplies should be turned on and off for power cycling. You do not need a power sequence for this device, it's just that analog output voltage and some other voltages in the specifications are dependent on Vcc or Vdd. Thus, simultaneous power up is recommended, but so long as the application is not beginning before both Vcc and Vdd are present, there should be no issues. The timing of the reset will follow the power-on reset sequence as mentioned in the datasheet. I understand the datasheet is not clear on the details of power supplies, but here is an app note discussing TI audio codecs with Vdd and Vcc supplies. The PCM1798 is a type-2 product as described in the document.

6740.PCM1xxx_Power_Sequencing_AppNote.pdf

Please let me know if you have further questions. Thanks!

Regards,

Brian Wang

Audio

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Inconsistent Dynamic Range on PCM1798