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OPA855: OPA855 has a peak voltage output when enabled

jeno.zhang
Expert 1785 points
Part Number: OPA855

Hello,

The OPA855 has a relatively high power consumption, and the customer uses the enable function. When enabling the operational amplifier, the output has a peak voltage (300mV-400mV) and a downward probe negative voltage. After about 70us, the output voltage returns to normal, Please help analyze the cause。

Thanks！

  • 0
    Guru 140200 points

    Hi Jeno,

    the performance of OPA855 during power down very much depends on the actual circuit and the input and output signals. So, without additional information no satisfying answer can be given. Please provide more information (schematic, scope plots, etc.).

    Keep in mind that this is a power down feature in order to minimize the current consumption of OPAmp. But this is no output multiplexing feature. It may be used for output multiplexing but will satisfy only when certain conditions are fullfilled. A performance like shown in figure 7-23 and 7-24 can only be achieved when exactly the same conditions are fullfilled, which means "VS+ = 2.5 V, VS– = –2.5 V, RF = 453 Ω, Gain = 7 V/V, RL = 200 Ω" and in combination with an output voltage swing of 1Vpeak.

    Keep in mind that at higher signal levels internal protection diodes may become forward biased potentially ruining the performance. Read section 9.4.2 of datasheet.

    Kai

  • 0
    TI__Mastermind 22280 points

    Hello Jeno,

      Agreed with Kai. Is there an input signal applied during the enable and disable function? If the same signal is also present when device is disabled; is there an output? 

      Kai and Bharat recently went into details on the internal ESD diodes for a device with a similar enable/disable functionality at this e2e thread. 

    Thank you,
    Sima