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ADC0809-N: Timing check for ADC0809

Part Number: ADC0809-N

Hi team,

My customer is using the ADC0809, and they find that the START signal can't meet the requirement of our datasheet.

But it seems the operation of ADC0809 is OK, now they want to know if there is risk for some functions.

The schematic is as below:

The problem of the START signal is that:

1. There is a 2ns overshot in START(the yellow one), the voltage of the overshot has reached to -3.28V(as below)

The Ts is about 248ns, the Th is 560ns, all is larger than 50ns.(as below)

The yellow one is the START signal, the blue one is address signal.

3. They use the START signal to for the ALE signal.

Please help to check the timing and comment if this is a risk for above three timing problem

Lacey

Thanks a lot!

  • Hi Lacey,

    I'm not to concerned about the setup and hold times, the MAX value in the datasheet is from the way National used to define these parameters over temperature. The voltage levels are another story though. What is the cause of the slow ramp up? Normally the START and ALE would be from a GPIO on a micro-controller, with well defined/behaved rise and fall times. If you really are driving those pins to -3.28V, you can damage the device - it may work for a while, but long term reliability is not guaranteed. Depending on what it is driving that pin, you might be able to get by with some termination (series R or small R/C filter) or you may need to diode clamp it.