I have connected AD9280 in top/bottom mode using external reference (1V) on REFTS/REFBS. The device is powered on using 5V supply. When I turn the supply on, with 1Vp-p input at AIN, I don't see output until after 131 seconds!
I am only using 4 MSBs of the output. Output D7 stays high for 131 seconds, D6 and D5 toggles but mirror each other. D4 is same as D5. After 131seconds the output looks ok. Without going in further detail can I please ask, what is the reason for the 131seconds delay? Why D7 stuck to high after power up?? Also, any clue for the odd behaviour of D4, D5, D6? I have checked these lines are not shorted to high or each other as the do toggle after 131 seconds. Please help. Thanks,
No fundamental reason why any delay on the order o 131 sec if device is configured per datasheet recommendation. Note that these devices are tested at the factory for a wide range of the DC and AC specifications listed in the datasheet with test time per unit being on order of a few seconds!
Suggest reviewing the datasheet and ensure that all external required components are installed as well as correct DC voltages appear on all supply pins and analog input/output pins.
Thanks for the reply. The connections in my test circuit are listed below:
-- AVDD/REFSENSE/MODE tied to 5V supply
-- DRVDD tied to 3V3 supply. 3V3 and 5V ground connections tied together
-- AVSS/STBY/DRVSS tied to GND
-- 1V external reference provided to REFTS. REFBS connected to ground.
-- REFTF and REFBF decoupled as per figure 21 on page 12 of the AD9280 datasheet.
-- OTR, VREF, CLAMP, CLAMPIN are not connected to anything
-- only D7-D4 lines used in design so D3-D1 are not connected to anything
-- 1V p-p sinusoidal input is provided at the AIN pin
-- a 14MHz crystal is connected to CLK
-- THREE-STATE pin is tied to GND
Please let me know if any of the connection is wrong.
Also, I read 3V on REFTF and 2V on REFBF. Is this correct? Should it not be same as REFTS and REFBS respectively?
Thanks again for the reply and your quick help.