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OPA858: Regarding transient time latency of power down feature

Deepak Sharma
Prodigy 235 points
Part Number: OPA858
Other Parts Discussed in Thread: TLV3801, TINA-TI

Hi TI

We need to thoroughly examine the transient time characteristics of the OPA858 in relation to the power_down enable/disable feature. Specifically, what is the maximum time it takes to make transition from the off to the on state (here ON state is fully operational stable state)? For our high-speed application, we intend for this transition to be in the order of sub-nanoseconds. Additionally, what is the typical value of output impedance it offers in power-down mode?

Thanks and Regards

Deepak

  • 0
    Guru 269710 points

    The specified turn-on delay (where the output reaches 90 % of the final value) is typically 13 ns.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    Can the power down pin of opa858 be driven from an analog comparator with LVDS output, for example, with #TLV3801#?

  • 0 in reply to Deepak Sharma
    Guru 269710 points

    The switching thresholds are 0.65 V and 1.8 V. This range is larger than the what an LVDS output can provide.

  • 0 in reply to Clemens Ladisch
    Prodigy 235 points

    What is the typical output impedance of the OPA858 in power-down mode? How can a 13 ns delay be simulated in TINA-TI using the power-down feature? I couldn't find a way to access the PD pin. Can you please assist?

    Thanks and Regards

    Deep

  • 0 in reply to Deepak Sharma
    TI__Genius 9790 points

    Hi Deepak,

    The output impedance was not captured in the datasheet, but the designer said it would be in the 100k-ohms range. However, when looking back into the part the impedance will be the feedback network as the impedance looking into the device would be significantly higher. As for the power down pin, it was not modeled in the OPA858 model, but information and graphs were captured and are highlighted in the datasheet. For understanding performance and behavior when turning off/on the device, we recommend testing the real silicon as some of our models that do implement this feature do not fully reflect the behavior of the actual device.

    Best Regards,

    Ignacio

  • 0 in reply to Ignacio Vazquez Lam1
    Prodigy 235 points

    Hi Ti

    During power down mode, What is the typical current that gets sink into the output terminal of the op-amp when an ideal current supply is provided at the inverting input terminal in a TIA configuration? Does any alternative part provide an output resistance greater than 1 Gohm in power-down mode?

    Thanks and Regards

    Deepak

  • 0 in reply to Deepak Sharma
    TI__Genius 9790 points

    Hi Deepak,

    We don't have something like this specified in the datasheet because it depends on the nodes around the amplifier so this is not something that would be stated. As for the alternative device, we do not have any device with this high of an output resistance, most of the devices will be in the range of OPA858.

    Best Regards,

    Ignacio