Please let me know about the threshold of mode pin in AD9237-40.
Datasheet P.20 describes below but does not describe threhold.
Mode2 ; Span ; Power scaling
AVDD ; 1; Disabled
2/3 AVDD ; 1; Enabled
1/3 AVDD ; 2 ;Enabled
AGND ; 2 ;Disabled
We would like to use Span factor 1 and power scaling enable.
But, board space is too short and it is difficult to make 2/3 AVDD from AVDD(3.3V).
So, if possible, we would like to supply 2.5V (another power rail) to MODE2 pin.
As the result of our test, Span factor 1 and power scaling enable is set by voltage less than 2.6V.
Could you give me your advice if there is any problem ?
Thank you for using the AD9237.
Applying 2.5V to the MODE2 pin will not damage the part as long as the AD9237 is powered up before the 2.5V source.
From your testing, you have about 100mV margin at 2.5V. To increase your margin, you could increase AVDD to 3.6V. This would give you another 2/3 * 300mV = 200mV margin. You could also add some series resistance to your 2.5V source.
Ultimately you will need to ensure that MODE2 = 2.5V passes your internal system/quality requirements, but in any case MODE2 = 2.5V will not be a damage risk problem for AD9237 as long as the ADC is powered up before the 2.5V is applied.