PCM2706C: Bus-Powered VDD Current Capability

Evan Cornell

Part Number: PCM2706C
Other Parts Discussed in Thread: ISO7340-Q1, PCM2706

I plan to operate PCM2706C in bus-powered mode as a USB-to-I2S transport with digital isolation.

Can the internal VDD regulator of PCM2706C supply enough current to power VCC1 supply of ISO7340-Q1 (listed as 1.3mA @ 10Mbps)?

I would be passing PCM2706 DOUT, I2S bit clock, I2S frame sync, and SSPND_N signals through ISO7340-Q1.

Side question: can C_VCOM be changed to 1uF ceramic cap if DAC outputs are not being used?

over 2 years ago

0 Arash Loloee over 2 years ago

TI__Mastermind 19390 points

Hello Evan,

Data sheet doesn't have any spec on drive capability of internal supplies, going true datasheet I did not find any info about the internal regulator of it , but I believe it is too much current that it can be supported.

I believe you can change the VCOM cap to 1uF .

Regards,

Arash

0 Evan Cornell over 2 years ago in reply to Arash Loloee

Expert 1380 points

Can you please check with design team?

I see the supply current for overall part (presumably the sum of VCCP, VCCL, VCCR, and VDD) is up to 46mA, so I would think if the DAC output is not being loaded, I ought to be able to tap off 1.3mA.. would it be better to use a different PCM2706 regulator output pin for this purpose, besides VDD?

Thanks!

+1 Arash Loloee over 2 years ago in reply to Evan Cornell

TI__Mastermind 19390 points

Evan, sorry I misread it as 1.3A not 1.3mA,! just by looking at this number you should be able to drive it with VDD . By the way, this is an old design and vary difficult to find the original design team. I would use VCCP or VDD , instead of VCCL and VCCR as I rather have identical loading on the Analog power supplies for both channels.

Regards,

Arash

0 Evan Cornell over 2 years ago in reply to Arash Loloee

Expert 1380 points

Arash,

Could you please comment on the attached schematic snippet?

Thanks,

Evan

0 Arash Loloee over 2 years ago in reply to Evan Cornell

TI__Mastermind 19390 points

Hi Evan,

Sure, I will take a look at by Wed (or sooner) and reply back to you.

Regards,

Arash

0 Arash Loloee over 2 years ago in reply to Arash Loloee

TI__Mastermind 19390 points

Evan, just couple of suggestions:

VCOM cap needs to be more, 10uF
Any filtering at the output? ( you can take a look at user's guide at User's guide for more information

Regards,

Arash

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PCM2706C: Bus-Powered VDD Current Capability