Low voltage USB Audio design Topic is solved

[maxter]

We are thinking of making a low voltage USB Audio unit, using wherever possible 1.8V components, and I have a couple of questions:

• I have seen that there is a 1.8V equivalent of one of the natively supported Flashes (W25Q16JV) the W25Q16JW and I was wondering if it could be a direct replacement of the supported version; what makes me uncertain is that the libquadflash page in the documentation (here) mentions "libquadflash supports a wide range of flash devices available in the market. Devices with SFDP capability expecting 6 dummy clock cycles .... " but both the datasheet for the Winbond memories mention in the SFDP register description "Eight “dummy” clocks are also required before the SFDP register contents are shifted out ...".
  Is the 1.8V Flash (W25Q16JW) compatible with libquadflash?

• Does the USB module in the XCORE.AI require 3.3V or can it run all at 1.8V?

[Joe]

Yeah 1.8V is no trouble at all. See here for an example hardware design using 1.8V IO and the flash you mentioned.

https://www.xmos.com/xk-voice-l71

Agree the docs aren't clear on the dummy cycles. They are referring to the number of dummy cycles used with the 0xEB quad fast read command rather than any dummy cycles associated with the SFDP command. Will get the docs updated.

To run any form of USB you always need a 3.3V supply from somewhere as this is used for the basic signalling level in full speed mode. This is used to then negotiate to high speed (if used) which uses the 1.8V supply for signalling current. The device has separate pins for each of these supplies. The current they use is specified in the datasheet. Obviously if you're not using USB you don't need those supplies and could run the whole device on 1.8V (and 0.9V).

If you're moving to 1.8V for lower power, note the latest sw_usb_audio has new features to enable lower power systems.

https://www.xmos.com/file/sw_usb_audio- ... sign-guide

Cheers,
Joe

[maxter]

Many thanks Joe for the clear and exhaustive reply as always (and for acknowledging my confusion on the documentation :D )