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LM285-1.2: TC issue for LM285D-1.2

Jason Chien42
Expert 1180 points

Part Number: LM285-1.2

Dear Sir:

                  We used LM285D-1.2 for voltage reference and I find out TC characteristics is +(-) 20ppm/C in datasheet. I try to reference document of Slyt183 to calculate TC as below:

 

TEST CURRENT Iz=0.236mA

Vo1=1.2328V, (@25℃  1hrs)                Vo2=1.2292V (@50℃ 1hrs)

          T2=50℃ ,T1=25℃

TC=(Vo2-Vo1)/((T2-T1)*Vo1)

TC=-116.8ppm

The result look like over spec , What's wrong for my calculation? Do you have any suggest to us?

Jason

              

  • 0
    TI__Mastermind 19580 points

    Hi Jason,

    The +/- 20ppm/C average is calculated over the whole temperature range but individual temperature segments can have higher ppm... or lower ppm. If you increase the temperature range, the results still start to get closer to average.

    -MZ

  • 0 in reply to Marcoo Z
    Expert 1180 points

    Dear Mz:

                   Thanks for your reply. this is a helpful information for me.

    Jason

  • 0 in reply to Marcoo Z
    Expert 1180 points

    Dear MZ:

                  We tried to increase the test temperature ranger to -30℃~+85℃. But , the results still out of spec with datasheet . Do you have any suggest to us? or what's wrong for our test condition? Below is our formula and test results for your reference. Thanks!

    Average TC (ppm) = ((Vmax-Vmin)/V25℃)/(Tmax-Tmin)*106

    LM285D Avg. TC = ((1.2392V-1.2272V)/1.2359V)/(85℃-(-30℃))*106 =84ppm

  • 0 in reply to Jason Chien42
    TI__Mastermind 19580 points
    Hi Jason,

    Really odd this is happening. Can you try another unit?
    Also what package is this?

    -MZ
  • 0 in reply to Marcoo Z
    Expert 1180 points

    Dear Mz:

                    We  tried 4 unit of LM285D_1.2 but Their TC all of out of specification with datasheet as below table and picture. We also tried LM385 (TI) base on same condition and it meets specification with datasheet as last picture. Do you have any suggest to us? Contact TI QC? BTW, those LM285D package are SOIC-8.

    Best Regard

    Jason

  • 0 in reply to Jason Chien42
    TI__Mastermind 19580 points

    Hi Jason,
     
    After looking over your new data, I reviewed this with my internal team. The LM285-1.2 specs 20ppm/C as typical and no maximum is specified, therefore your values are close to what I would expect if I compare other devices typical to maximum. But since all your devices are definitely outside typical, It is not a bad idea to contact TI CQ. If you need help choosing the right device, because it seems the LM285-1.2 temp co is not what you are looking for, I am free to help.

    -MZ