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aVZ calculation of LT1009IDR

ttd
Mastermind 7670 points

 

Dear Technical Support Team,

 

I have a question about LT1009IDR.

 

Dose aVZ spec of datasheet include ΔVZ(temp)?

 

I think that 2.525V and 2.475V(Full range of D/PW package) includes ΔVZ(temp).

(Change in reference 15mV from Vz of 25℃(min 2.49 / max 2.51 max))

So I tried to calculate from -40℃ to 85℃ for LT1009IDR(D package).

 

|aVZ| =(((2525-2475mV)/2500mV) x10^6) / 125℃= 160ppm/℃

 

But it didn't much aVZ spec of datasheet (typ 20,max 35 ppm/℃)

How should I calculate correctly?

 

Best Regards,

y.i

  • 0
    TI__Mastermind 24485 points
    Hello Y.I.

    The aVZ specification is a complementary specification to the ΔVZ(temp).
    Please see table note 2 in the datasheet for the description of how the ppm is calculated.
    Does this make sense?

    The following application note may also help to further understand.
    www.ti.com/.../slva445.pdf
    There are a number of specifications to consider when calculating worst case variation in the reference.

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Mastermind 7670 points

    Hi Michael,

    Thank you for your reply.

    I tried to calculate following with note 2.

    |aVZ| =(((2525-2475mV)/2500mV) x10^6) / 125℃= 160ppm/℃

    Is it correct calculation?

    Best Regards,

    y.i

  • 0 in reply to ttd
    TI__Mastermind 24485 points
    Hello y.i,

    This is not the correct calculation. You are using the Vz specification to try to calculate the aVZ spec.
    The Vz specification is the general accuracy specification of the device at 1mA, and this can be across temperature. This does not imply that both the minimum and the maximum Vz of the device will actually hit these limits. In fact, it is not likely to be even close to these limits across temperature.
    It is actually the case that the variation over temperature is less. When looking at the variation across temperature you should look at the DVz(temp) specification, and this spec is what is then used to calculate the aVZ value that you are looking for.

    Does this make sense?

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Mastermind 7670 points
    Hi Michael,

    Thank you for your answer.
    I understand my calculation isn't correct.
    So I have two questions.

    1.)
    Is it ok to use 125℃(-40 to 125℃) for ΔTA?

    2.)
    Datasheet describes following example.How do I know about "maximum VZ = 2501 mV at 30°C, minimum VZ = 2497 mV at 0°C"?
    Can I get VZ of each temp like 30℃ or -30℃ and so on for LT1009I?

    For example, at IZ = 1 mA, maximum VZ = 2501 mV at 30°C, minimum VZ = 2497 mV at 0°C, VZ = 2500 mV at 25°C, ΔTA = 70°C for LT1009C

    Best Regards,
    y.i
  • 0 in reply to ttd
    Mastermind 7670 points
    Hi Michael,

    How about above questions?
    If you answer those , I could understand calculation.

    Best Regards,
    y.i
  • 0 in reply to ttd
    TI__Mastermind 24485 points
    Y.I.

    It is ok to use 125C for ΔTA, but I believe you mean -40C to 85C.

    We do not provide information of Vz at specific temperatures. You can find the potential error of a reference based on the application note that I posted previously.

    In general the device has an initial accuracy where the device can fall anywhere within the Vref tolerance. Once you have this initial accuracy the voltage can then vary over temperature, loading conditions, as well as Vka voltage.

    Best,
    Michael