Is the CLKMODESELECT pin on AD9951 3.3V compatible or only 1.8V compatible? Applying 3.3V on this pin seems to cause latchup of the whole device.
It turns out the AD9951 and AD9954 are very similar devices. As such, the CLKMODESELECT pin on the AD9951 is NOT 3.3V tolerant (like the AD9954).
Admittedly, the data sheet is not particularly clear on this. My interpretation is that DVD_IO establishes the logic level functionality for all of the I/O pins (I would consider CLKMODESELECT an I/O pin).
That said, if DVD_IO is 3.3V, then I would expect CLKMODESELECT to be 3.3V compatible. However, if DVD_IO is 1.8V, then I would expect a 3.3V signal on the CLKMODESELECT is unacceptable.
The reason why I'm asking is we have found the part to behave strangely, as if 3.3 V on that pin caused latchup. In datasheet for AD9954, there are several mentions that this pin is not connected to the VDDIO, but to VDDA - thus only 1.8 V tolerant. I found mention on this forum that this should also apply to AD9953 and one FAQ article stating that on AD9952, this pin should be tied to VDDIO (if it is to be used) either directly or through 1k resistor. However it does not state when one should use the resistor (I personally think that they didn't want to mention this little flaw). But nothing regarding AD9951.
Maybe I should also mention that we are being ignored by AD with this question for over a month - we tried using e-mail, FB personal message, public Twitter statement (twice) with no response whatsoever.
I apologize for the apparent lack of response as we strive for excellent customer support. Rest assured there is no purposeful intent to ignore your queries. However, I am not sure that FB and Twitter constitute our official channels of communication on technical matters. This forum is your best source of technical assistance.
In any case, I am not an expert on this particular part, but I will check with our design folks to see if I can obtain a definitive answer for you within the next 48 hours.
Follow up question: What supply voltage(s) are you using for AVDD and DVDD?
If you are employing multiple supply voltages, then please specify the voltage applied to each AVDD/DVDD pin.
Thank you for your final response, which forces me to have 2 additional questions:
Will this be added to the datasheet or will the datasheet stay incomplete?
Will AD refund devices damaged by the non-complete datasheet (or at least apologize)?
To answer your previous question, AVDD and DVDD were both 1.8 V, DVDD_IO was 3.3 V.
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