Is there IQ input biased internally for ADL5371?

Document created by analog-archivist Employee on Feb 23, 2016
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I use ADL5371 in my product following EVB schematic. I tested with my board and
found that there is about 1.7V~1.9V DC output from the IQ input ports and the
current consumption of the part is about 260mA, which should be 175mA specified
in the datasheet. Then I did another test. I connected IQ input ports to ground
with 50ohm resistors and also add 500mV DC bias to the input ports, I measured
there is 2.6V DC at IQ input ports and current consumption is 150mA.
To be honest, we don’t have ADL5371 EVB in hand and no experience to this
issue. Could you please help give some comments on it?


IQ inputs are not biased internally. That’s why it is needed to bias to 0.5V
externally. There is no voltage output at IQ inputs. There should be 0V when
power supply(5V) is supplied to ADL5371 (I checked it with evaluation board).
When there is 1.7~1.9V at BB inputs, current could increase to around 260mA as
you have seen(I also confirmed it with evb). But it is abnormal case and it
should be 0.5V not 1.7V at BB inputs anyway. Need to figure out where 1.7V is
from. I am not sure there is 1.7V when the part is damaged. So please check if
it happens at just one part or many parts. But before that, please make sure
how customer checks the voltage at BB inputs of ADL5371 . Did they check it at
the case that DAC is connected or not?  It is possible that 1.7V is from DAC.
So please check voltage by disconnecting DAC if it is connected.