From EVAL-ADAU10701MINIZ to a project... (part 2)
Hi,
I have a few other questions and I was wondering if someone can help me:
1) If the circuit/application doesn’t need a reset button, it is possible to:
- remove the ADM811TARTZ
- connect directly *BRD_RST from the USBi connector to pin 5 of the ADAU1701.
2) Just to be sure before I move forward in the PCB/circuit design. If the circuit has an external power supply and considering it looks like the USB_CLK signal from the USBi is not used, are the only connections needed from the USBi:
- SCL
- SDA
- *BRD_RST
- GROUND
3) If the circuit doesn't use write-back, should pin 20 (WB) of the ADAU1701 connected to ground?
4) I asked this questions in the past but I don't think anybody answered. I can't find the output impedance of the VOUT0...VOUT3 pins. Does anybody at AD know the value?
Thanks
3.3V
Audio Signal Processors
SigmaDSP Audio Processors
adau1701
Hi Brett,
Thanks for your help.
The idea is to create a variation of EVAL-ADAU10701MINIZ tailored to my applications and connect it to the USBi in order to debug/program it.
1) 2) I guess that with my project, connecting USBi/BRD_RST and pin 5 of the ADAU10701 shouldn’t do any harm. I was a little unsure about the signal inversion of BRD_RST. I’m happy to hear that the two can be connected directly without any extra component/part.
3) Excellent.
4) From my viewpoint, it is a little bit odd that it is not part of the datasheet.
Reading the datasheet at page 21, it is not unreasonable to expect that the EVAL-ADAU10701MINIZ implementing the very same filter, should cut at 50 kHz (560R/56nF). In practice, the same filter, in the evaluation board, cuts at a lower frequency (-1dB @ 9 kHz, -3dB @18 kHz)
I believe this is due the combination of the comparatively high out impedance of the ADAU1701 and R11/R12.
Apart from the possibility of a misunderstanding, as far as I can see, it is impossible to design a passive RC low-pass filter on the output without knowing the output impedance.
It is not the end of the world but, IMO, it might be a good idea clarify that the filter suggestion in the datasheet does not produces a 50 kHz cut if used with the ADAU1701.
Having said that, if my observation of the frequency response of the out filter of the EVAL-ADAU10701MINIZ are correct, the out impedance should be in the region of 170 ohm. I hoped that someone at AD could confirm it but I gather it is not a piece of information available.
1) In a standalone system where reset is not required, you can simply tie the reset line high at all times with a pull-up resistor. You can connect to BRD_RST if you want to use the software controllable reset function in SigmaStudio.
2) Correct. BRD_RST is optional.
3) Yes.
4) Output impedance of the VOUTx pins is not characterized in our manufacturing tests and therefore does not appear as a spec in the datasheet. You can do a simple output impedance measurement to determine the typical value, which should be in the range of several hundred ohms.
Hi 3.3V,
That makes sense. I will ask the design team to see if we have a range for the output impedance that is expected by design, even though this value is not measured in production testing.
BrettG wrote:
That makes sense. I will ask the design team to see if we have a range for the output impedance that is expected by design, even though this value is not measured in production testing.
Any update? I'd also like to know the ADAU1702 output impedance typical value.
Hi,
The output impedance for the ADAU1701 and ADAU1702 are approximately 100 ohms.
Best regards,
Coleman
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