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OPA569: Parallel operation but one is enabled and the other is disabled

Danilo A.
Mastermind 24715 points
Part Number: OPA569

Hi Team,

We have received this inquiry from our customer,

Consider a circuit with two OPA569 power amps (Parallel Out pins connected to each other) below, although ENABLE is not shown - if A1 is disabled via ENABLE pin, what would be the impact on the active A2 (other than less output current)? Could A2 function independently (provide power to R-load) with A1 disabled or would we have a degraded output on A2? 

I understand that the OPA569 can be used for multiplexing as stated at page 14 of the datasheet but it seems that it doesn't meet the second design consideration at page 2 of the article, "Using Operational Amplifiers as Multiplexers in Cost Optimized Designs", below because it has an input clamping diode. Can you please confirm if the OPA569 can be used in parallel configuration while one is enabled and the other one is disabled? 

https://www.ti.com/lit/an/sboa311a/sboa311a.pdf

Regards,

Danilo

  • 0
    Guru 140200 points

    Hi Danilo,

    why would someone want to do that?

    Kai

  • 0
    TI__Mastermind 48076 points

    Hi Danilo,

    Generally, we do not recommend to configure parallel op amps that driving a load. The reasons behind it are explained in the attached application note, where power amplifier A1 and A2 may "fight" against each other depending on its output impedance and/or the load. It will be better to have a single power amplifier to source/sink the required load current. 

    https://e2e.ti.com/blogs_/archives/b/thesignal/posts/paralleling-op-amps-is-it-possible

    Could A2 function independently (provide power to R-load) with A1 disabled or would we have a degraded output on A2? 

    Since I do have the  specific load requirements, I can only answer the question in general. Based on the output impedance figure at the disabled mode, A2 op amp under the parallel configuration should work independently and source the required current to R-load.  Opposite may be true as well, if A2 is disabled. 

    Please provide us some application requirements and we should check it out the operation scenarios.  

    Can you please confirm if the OPA569 can be used in parallel configuration while one is enabled and the other one is disabled? 

    Could you provide us with more specific switching application and load current? Yes, Mux-Friendly amplifiers and Using OPs as multiplexers are talking about higher frequency (~10MHz range) in Mux application. OPA569 's BW is approx. 1MHz range; and this is likely high current, low voltage switching application, where high switching speed may not be applicable.  OPA569 has much fast t_disable time than t_enable time by a factor of 30X, so I prefer not to speculate possible interference between switching events. It would be more feasible to discuss the actual load, timing and actual switching events, perhaps I can demonstrate it via a simulation.     

    Best,

    Raymond