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Start Up Time and Input Signal Without Power Safety Questions

Darren O'Connor
Prodigy 70 points
Other Parts Discussed in Thread: ADS5463-SP, ADS5444-SP, ADS5463

Hello,

I am considering using the ADS5444-SP or the ADS5463-SP ADC converters in a space application. To limit power, I would like to power up the devices only when I have a signal event that I need to measure. While powered off, my first question is whether or not I can still have the clock and analog input signals be active without damaging or degrading the part? My 2nd question is how long after the power supply turns on will the device put out accurate data? I realize both parts have a data latency, which I am not concerned with. My question is really how long after the power supplies are settled can I expect to get good data out of the parts?

Thanks in advance, Darren

  • 0
    TI__Expert 8895 points

    Hi,

    I do not think the device will be damaged from analog input and clock while power down. We sometimes leave the device in this situation but there has been no problem. I'll check this with test team.

    ADS5463 has internal power-up time, 200us, from power supply and 3.5 clock cycles of data latency.  ADS5463 requires a sequence of power-up as below and also you can refer to the page 37 of datasheet for more information.

    - Power up both AVDD3 and DVDD3 at the same time (best scenario), or

    - Keep the voltage difference less than 0.8V between AVDD3 and DVDD3 during the power up (0.8V is not a hard specification - a smaller delta between supplies is safer).

    Thanks,

    KW

  • 0 in reply to KW Nam
    Prodigy 70 points

    Hi,

    I'd still like to know if this part would start up faster if the clock input was held static, rather than powering the device up. If we did leave power on but not clock the device:

    1. How long would it be after the clock signal came on until we could expect good output ADC conversions?

    2. How much quiescent power would be used when the clock was held static?

    Thanks, Darren

  • 0 in reply to Darren O'Connor
    TI__Expert 8895 points

    Hi, Darren

    I will get back to you hopefully soon after discussing this with designer of these devices.

    Thanks,

    KW

  • 0 in reply to KW Nam
    Prodigy 70 points

    I'm still waiting to hear what the quiescent power would be if the input clock were held static while the device is powered? And how long after starting the clock in such a configuration (powered but clock static) would it take to get data at or approaching the specifications in the data sheet?

    Thanks, Darren

  • 0 in reply to Darren O'Connor
    TI__Expert 8895 points

    Hi, Darren

    When no power is applied, all of the references are off. The reference have large RC time constants for noise suppression, so these all have to charge up when power is reapplied. This takes up to 50us for the guaranteed SNR of sampled data.

    Regarding power consumption of ADS5463, typical value is 2.18W and max 2.4W at 500Msps.

    Thanks,

    KW

     

  • 0 in reply to KW Nam
    Prodigy 70 points

    Hi KW,

    I am still hoping you might answer the question: Does the power consumption decrease if the part is run at a lower sample rate and is there a curve of power consumption vs sample clock rate?