Interfacing ADAU1701 with AD1955 (2)
As a bit of a continuation from Interfacing ADAU1701 with AD1955
Has anyone successfully used an ADG3304 for I2S level translation from an ADAU1701? Or could anyone offer an educated/experienced guess perhaps, as to the feasibility. Dr. Ram expressed concerns about the ADAU1701's drive voltage, I noticed he said he'd try it and post back if it worked...and didn't! (May well have forgotten though).
When buffering the OSCO output should there be a 3.3V to 5V level translation happening? (Fairly new to digital and clocks so apologise if this is basics, couldn't find an answer elsewhere though). Perhaps this could be done with the 4th channel of the ADG3304?
Thanks again.
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Hi,
The Vih input spec for the ADG3304 is 2.2 V, however the Voh spec for the ADAU1701 is 2.0 V. A direct connection *might* work but the most reliable solution would be to use a level translator as you suggest. The PLL and Clock Oscillator in the ADAU1701 are in the analog domain, and so should run at 3.3 V, however the OSC loop is very sensitive. A buffer between these devices is definitely recommended.
The ADG3304 looks like a good choice for level translation between the ADAU1701 and AD1955. Two factors that I checked:
Speed of the ADG3304 - rise and fall times are 2 - 4 nS. This will be quick enough for the fastest clock in the system.
Drive capability - While the specs do not detail the drive current, the eye diagrams show good performance under a capacitive load. I would recommend that you apply basic series termination in your design by inserting a 22 ohm resistor in each path between clock/data sources and loads. The value of 22 ohms might need to be be adjusted once the boards are built; use of an active probe on each net will show any over- or under-damped conditions that can be improved by adjusting the resistor value.
Since the maximum digital input level for the ADG3304 is Vcc+0.3V, you will not be able to use the same level translator for both OSCO and your I2S clocks/data. I would look at a single channel level translator for OSC, and use the ADG3304 for the BCLK, LRCLK and SDATA.
I hope that this information helps.
Regards,
Coleman
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