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TLV9054: Amplifiers forum

Prodigy 120 points

Replies: 21

Views: 216

Part Number: TLV9054

Dear Sir,

refer to attached file, it is my circuit for the front end of ADC.

I have request PTLV9054 and TLV9054 samples for this front end circuit. Please refer to attached picture for these 2 OPA.

test condition: CH0+-=100mV, ADC is calibrated by ADCMT 6156.

test result:

1. PTLV9054: ADC read 9999~10001. and the result is stable

2. TLV9054: ADC read 9995~10005. and the result is not stable.

7317.OPA.pdf

21 Replies

  • Hello Allen,

    Did I get the equivalent circuit right? What was the selection for the resistors? Were both tests with the same resistor setting?

    If the VIN was +100mV and 0mV (different than the schematic) then the "unstable" would be +/-50uV (noise) 

    How many TLV9054 have this observed behaviour? Does an ABA swap show that the behaviour follows a specific TLV9054?  https://training.ti.com/troubleshooting-tips-ic-b-swap

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Dear Ron,

    All of the resistors are 1M for measuring 100mV.

    I have done A-B-A test.

    I made 2 PCBA. And they have the same problem.

    Then I change TLV9054  to PTLV9054. the read value is more stable.

    Becuase I only request 5 pcs PTLV9054. And I only have 2 good samples for this testing.

    thus, I can't do more A-B-A tests.

  • In reply to Ron Michallick:

    Dear Ron,

    refer to ADC read value, the noise is about 50uV @OPA is TLV9054.

    But I hope the read value varied < 20uV.

    the ADC has the digital filter and PGA inside. I set PGA gain=8 for measuring 100mV.

    As I tested 4 kind of OPA, I found that TLV4314 and PTLV9054 can meet my spec.

    OPA4314 and TLV9054 can't.

    Could you explain it?

    And what difference between PTLV9054 and TLV9054?

  • In reply to Allen Huang65:

    Allen,

    PTLV9054 and TLV9054 are the same other than the former was in pre production status. TLV4314 and OPA4314 will have the same expected noise level. I see that the application attenuates the high frequency input signal well (LPF = 16Hz) . -78dB at 10kHz

    [If pictures look blurry, click on them to open a clear version]

    [edited] However the op amp noise gain is amplified wide bandwidth and the square root of this bandwidth is significantly large especially because the op amps tested are wide bandwidth op amps. Noise gain starts at +6dB and it will drop to 0dB noise gain near 100Hz and hold 0dB gain past 1MHz.

    The post filter (1k 100nF 1k) is helpful but that LPF doesn't engage until 800Hz (-3dB) the noise gain is reduced to -22dB by 10kHz

    Changing the 1k resistors to 39k lowers the output LPF down to 20Hz. noise gain is -3dB at 31Hz and drops to -90dB at 10kHz. I expect about a 6:1 drop in output noise (due to op amp) from this resistor change. 

    The forward signal gain bandwidth does drop a little to 11.4 Hz from the resistor change. 10kHz gain is -180dB at 10kHz

    The resistor change will bring down the noise significantly. The DC error should not be an issue as long as the ADC doesn't draw a DC current.

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    Dear Ron,

    I don't think that the low pass filter issue.

    I have removed the capacitors(10n & 100n) and the result is the same.(not change bad and not change good)

    And when I change OPA, the read value of ADC is stable @ capacitors are removed.

    So I think if I(bias) or offset is drifted. Or open loop gain is drifted.

    P.S.

    I have use 1%  and 0.1% tolerance resistors for testing. the results are the same.

    Vref is supplied by REF3325AIDBZR

  • In reply to Allen Huang65:

    Allen,

    I see; there was no change with or without caps.

    Simulated total noise with caps.  Just 2uV total noise

    Simulated total noise without caps.  Now 957uV total noise

    In summary, changing the op amp with one that has different symbolization on the top but equivalent performance on the inside makes a difference (is it the same difference for 9054 and 4314?).  Therefore something other than the op amp also changed.  Removing the capacitors did not make a change therefore I believe that op amp internal noise is not the root cause.

    Revisiting the original observation "2. TLV9054: ADC read 9995~10005. and the result is not stable."

    Does the reading randomly move throughout that range or does it only occupy a small portion of the range?

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Ron Michallick:

    it only occupy a small portion of the range.

  • In reply to Allen Huang65:

    Allen,

    I asked a colleague to take a look at this e2e thread to get a second perspective on this issue.  

    Regards,
    Ronald Michallick
    Linear Applications

    TI assumes no liability for applications assistance or customer product design. Customer is fully responsible for all design decisions and engineering with regard to its products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning Customer's design. If Customer desires engineering services, the Customer should rely on its retained employees and consultants and/or procure engineering services from a licensed professional engineer (LPE).

     

  • In reply to Allen Huang65:

    Hi Allen,

    that the result was the same when you removed the 10n and 100n capacitors makes no sense to me.

    Can you give us an exact schematic of the circuit which was used during the noise measurement? Where comes the 100mV input voltage from? How is it referenced to the circuit? How does the REF3325 circuit look like?

    Have you kept in mind that the REF3325 also produces noise and that the analog switches can inject noise into the signal path via the control inputs and the supply voltage?

    Kai

  • In reply to kai klaas69:

    Dear Kai,

    that the result was the same when you removed the 10n and 100n capacitors makes no sense to me. 

    -> Maybe the ADC has digital filter.

    Can you give us an exact schematic of the circuit which was used during the noise measurement?

    -> the noise can't be measured by my instruments. when I probe the OPA output, the read value of ADC will change. And the noise Vrms of  the different OPAs are similar.

    Where comes the 100mV input voltage from? 

    ->ADCMT 6146

    How does the REF3325 circuit look like?

    -> there are 1uF MLCC caps on the VIN and VOUT 

    Have you kept in mind that the REF3325 also produces noise and that the analog switches can inject noise into the signal path via the control inputs and the supply voltage?

    -> 1. I have change REF3325 to MAX6166. the results are the same.

         2. Because I can't measure the noise by my own instruments, I can't judge where the noise come from.

    below pictures are the schematic of VREF and PCB layout of OPA and ADC.

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