AD9520-3 EEPROM settings aren't loaded

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Accepted Answer

Question We are using an AD9520-3 Clock generator in one of our designs, but 
 unfortunately we are experiencing some problemen with respect to the loading of 
 the eeprom settings, stored inside the AD9520's eeprom memory.
 
 We have pulled the eeprom enable input high so it should load from the inside 
 eeprom.
 If loaded correctly everything works fine, but sometimes, one in 10 startups or 
 so, the eeprom settings aren't loaded and the AD9520 remains configured with 
 it's default settings. This situation is offcource highly unwanted, because the 
 chip doesn't function as expected in such a situation.
 
 Strangely enough I'm also able to replicate the problem by invoking a lot of 
 reset pulses on the reset pin, while keeping the chip powered on, then also 
 once in a while the AD9520 doesn't load its eeprom setting. It seems like some 
 form of faulty eeprom loading / reset recognition accurs. What I mean with a 
 lot of reset pulses: we've put a reset button on the PCB, by pressing it you 
 ground the reset input of the AD9520, if you press it really often in a short 
 period of time, we're also able to reproduce the problem, the "fail state" then 
 occurs once in a while. Maybe it has something to do with contact bounce of the 
 reset signal?
 
 I would really appreciate any help, I roughly followed the design of the AD9520 
 evaluation board and studied the datasheet, but I'm not able to see any 
 possible cause of the problem there. There is no mentioning of special reset 
 conditions or circuitry that should be required. Answer The threshold voltage at which the AD9520’s power on reset triggers is a little 
 on the low side if the power supply ramp is slow.
 
 We recommend leaving the RESETb line high during power-up until after the power 
 supplies are stable, and then use a >=20ns low pulse on RESETb.
 
 We’ve had a few other customers with this issue, and this has solved the 
 problem.
 
 Reset button on the PCB: Don’t do that. You can hang the RESET of the part or 
 hang the EEPROM I2C controller.
 
 On other comment: the input clock must be present when the EEPROM is loading, 
 as the VCO calibration depends on an input clock.

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AD9520-3: FAQ