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REF6145 Turn-On Time in Datasheet versus Simulation Model in TINA-TI ?

ngrkus
Expert 1020 points

Other Parts Discussed in Thread: REF6145, ADS8887, REF6125, REF6045, REF6025, LM4140, MUX36S08

Hello,

the REF6145 seems to be an ideal match for the ADS8887 I intend to use in my design. However I do require to have a startup time within the 0.1% error band of no more than 30ms.

Reading the datasheet it states 100msec (somewhat dependent on Cout and Imax?). Using the actual Simulation model from TI's website I get down to 10msec ??

Since the part is new I am a little confused. Is the simulation model far too optimisitc ?

br

Markus

  • 0
    TI__Mastermind 25075 points
    Hello Markus,

    The appropriate support has been contacted and should be in touch with you soon.

    Best,
    Michael
  • 0
    TI__Expert 5575 points

    Hi Markus

    Turn on time mentioned in datasheet is time required for REF6125 output to settle withing 0.1% of final value after we toggle the enable pin. TINA model does take into the account time required to enable internal bandgap once you toggle the input. Thats why numbers look optimistic with simulation model. What we mention in datasheet is actual numbers we get on setup. 

    Turn on time of 100ms is defined for REF6025 with Cout=47uF and SS pin open. With similar configuration on REF6045 turn on time is expected to be slightly greater than 100ms. I would recommend you to go by datasheet numbers.

    Can you please let me know what is the end application. As mentioned above you are pairing this up with ADS887, I would recommend you to take look at REF6025 EVM as this EVM uses ADC from same series (ADS888x).

    Please let me know if you need additional information.

    Thanks & Regards

    Abhijeet 

  • 0 in reply to Abhijeet Godbole
    Expert 1020 points
    Hi Abhijeet,
    thank you for your reply. We develop an isolated ultra low power acquisition system using the ADS8887. Overall power budget for the isolated version (4KV) is 20..25mW. A major contributor to this system is the reference and the input buffer.

    Too bad the new references do have such a long startup time. First measurement after initial power up must be no later then 30msec within the 0.1%...0.5% error band.

    I did check for the LM4140. A nice product I could make a fast low power and low noise reference for the ADS8887. However the "ee-based trimming" is being tested for the commercial temp range only?

    Do you have a similar product for the 'lower' industrial temperature range (-20..+85) ?

    br
    Markus
  • 0 in reply to ngrkus
    TI__Expert 5575 points

    Hi Markus

    Thanks for the information.

    I would like to highlight one point here. Usually to meet fast  current transients on REF pin of ADC, voltage reference output is often fed to high bandwidth buffer amplifier. REF6145 has this high badwidth  buffer amplifier integrated into the device and hence reduce component count and system complexity. For more information on this please refer to section 9.3 of datasheet

    If turn on time is your real concern then you can have look at REF5045. This series of references comes in standard grade (8ppm TC) and high grade (3ppm TC) Version and characterized over industrial temp range -40C to 125C. Device has faster turn on time of 200us.

    Can you let me know exact requirement on voltage reference (Temp drift specs, current consumption, noise spec, settling performance) you are looking at. This will help us to narrow down to most suitable device for your application

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    Expert 1020 points

    Hi Abhijeet,

    thank's for your reply. Yeah I'm aware of the nice features within the REF6x45 series of references.

    However the long startup time is a no go for our application.

    The REF5045 is our fallback solution. However if you only have ~20mW total power budget and your reference circuit is using half of it, you get the fealing it must be possible to do better. Please find attached the JPG showing the circuit I intend to use if there is no 5mW reference solution for my circuit. 5mW ist about the power I intended to spend for the reference. Then 5..7mW for the input buffer. The remaining mW for the input circuitry (including mux + digital isolators). The ADS8887 seems to us as a perfect fit. However to remain 'fair', a lot of the more power hungry circuits to reach the ADC's performance has been 'outsourced'. Therefore the 18Bit uPower ADC gets somewhat difficult to design.

    br

    Markus

  • 0 in reply to ngrkus
    TI__Expert 5575 points

    Hi Markus

    Composite buffer helps us to achieve true 18 bit performance out of ADC. For lower sampling speed you can think of having a single high bandwidth buffer at REF5045 output. DC performance may suffer and this can lead to some THD degradation. Also reference droop performance will also be degraded. What THD numbers you are targeting to achieve with your design. There is application note which describes performance of REF5045 with and without drive buffer. You can take a look at it

    Also what is the current MUX power consumption. You may want to take a look at TI's MUX36S08 which has typical quiescent current of 45uA.

    Hope this information helps

    Thanks

    Abhijeet