The datasheet for ADCMP572 curiously does not mention anything about maximum current/power in the input 50 Ohm termination resistors. For instance with VCCI=3.3 V, the other absolute max ratings seem to allow for input voltage to be as high as +3.8 V but I think that is probably not credible when the termination pin is grounded. That would be 76 mA or 290 mW.
Can someone clarify what is the real absolute maximum rating for these termination resistors? And could this be added to the datasheet please?
I am not asking about functional performance, only about damage levels. Trying to understand any possible power supply sequencing issues or other overload conditions in my design. The input signal will come from LMH6629 opamp with separate power supplies (probably +/-2.5 V).
The absolute maximum ratings are not the recommended operating conditions for any part.
"Stresses at or above those listed under Absolute Maximum Ratings may cause permanent damage to the product. This is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. Operation beyond the maximum operating conditions for extended periods may affect product reliability."
The input range recommended for VCCI=3.3V is only up to 1.2V so the current that should go thru the 50ohm input termination will be 24mA or a power dissipation of 28.8mW.
For the absolute maximum dissipation, yes your computation is correct which will be about 290mW.
Thanks and best regards,
I'm dealing with a signal that swings from 1.4 V to about 700 mV in the input of the ADCMP572. That is just above the 1.2 V recommended for the input voltage, and although I'm sure it wouldn't cause any catastrophic failure, I'm concerned that I may start losing part of the jitter and propagation delay spec if I go above the recommended specs.
I know the datasheet says that if VCCI =5.2 V the input voltage should be able to go up to 3.1 V, but I'd need another rail with a buck-boos converter to truly regulate at 5.2 V, and I'd need quite a bit of filtering to get that rail to be clean enough. The power in my design is supplied by a USB 5 V port, and if I could step that down with an LDO to, say 3.6 V or 4 V, that would be preferable.
Do you know what would be the VCCI necessary to accept up to 1.4 ~ 1.5 V input without risking derating the specs?
The max input voltage headroom is 2.1V, so for the input to accept 1.4 ~ 1.5V, VCCI should be 3.5V ~ 3.6V.
Thanks a lot for the quick feedback, the info is very useful.