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About the output impedance of VoutP of AD73322L

Category: Datasheet/Specs
Product Number: AD73322LARUZ


Could you please tell me about the output impedance of VoutP of AD73322L?

This is because VOUTP1 and VOUTP2 of the created board are connected.

Therefore, we are investigating whether a signal is being input to VOUP when either one outputs.

Best regards.

  • Hello baggio,

    This is a 20 yar old part so there are none of the original designers around to ask this question. I only have the datasheet to go by and to open up a design this old would take weeks and might not be possible. Design software has changed a lot since then. 

    I did notice an interesting specification and that is the Minimum Load Resistance of 150 ohms. This would have been there to limit the current/power output to a safe value. This means the output impedance is rather low. If you have a part in front of you then do an experiment. Place a potentiometer on the output. 10K ohm would be good and set it to 10k. Measure the output voltage with a scope. Then turn down the put until the voltage is half the voltage. Take the pot out of the circuit and measure it. It is now the value of the output impedance of the circuit. 

    That said let me comment on what you said:

    This is because VOUTP1 and VOUTP2 of the created board are connected.

    This is VERY bad. This is not how two signals should be summed. Perhaps the thought was to give it more drive strength by using two outputs together. As long as both channels are getting the same exact signal you can do this but it still is not great. There is always a small difference in the output of two different DACs. To "sum" them you really should have some resistance to decouple them. However, doing that will increase the output impedance. Therefore, if more current is needed then use an external OpAmp. 

    Also, keep in mind that the two DACs have out-of-band energy that also will be fighting each other if the output is not exactly the same. 

    Dave T