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REF5025: Can I tap a point from this to Voltage divider circuit of common mode voltage pin of a differential amplifier

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Replies: 6

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Part Number: REF5025

Hi TI Team,

I am using REF5025 as reference to ADS8900B. This ADC requires analog front end(using THS4551) which should be provided with a common mode voltage as Vref/2. So can I use the same REF5025 for Vref as well as common mode voltage divider?

Kindly refer the circuit and share your suggestion. And please comment whether the capacitors used in REF5025 are correct for my application.

Thanks,

Venkatesh P

  • In this case Vocm(common mode voltage) I should give to THS4551 1.25+0.1V OR 1.25-0.1V, So I took tap to a voltage divider circuit consist of two 1K resistor.
    If it is acceptable, can I use this same voltage divider circuit for my ? or should I use any buffer for stability?

    Thanks,

    Venkatesh P

  • In reply to Venkatesh P17:

    Hi Venkatesh,

    The REF50xx can be used with resistors and a buffer. Most applications for common mode voltage require a buffer due to the current consumption of the common mode pin. TIDA-01351 shows an example with the THS4551 and REF5025. www.ti.com/.../TIDA-01351

    The buffer is used to eliminate the IR drop on the resistor divider so I prefer the use of a buffer.

    The capacitors on the REF5025 look good.

    -Marcoo

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    If you feel your thread is resolved, please selected Answered.

    If you are using the TL431, check out the new TL431LI and its low Iq counterpart ATL431LI for improved system performance in a p2p package.

    Check out: Designing with the improved TL431LI for how to calculate worst case error on all '431 devices.

    Check out: Designing with the ATL431LI in Flyback Converters for tips and tricks on how to lower standby Iq to meet DoE and CoC regulations.

  • In reply to Marcoo Z:

    Hi Marcoo,

    Thank you.

    shall i proceed with the following design? Kindly refer if any discrete components value is mismatched.

    Thanks,

    Venkatesh P

  • In reply to Venkatesh P17:

    Hi Venkatesh,

    I would increase R10 and R11 to 20k Ohms minimum to reduce the current leakage of the device. Add a cap in parallel to the R11 for extra filtering if necessary.
    The OPA320 is fine, keep in mind any offset/noise error of the opa320 will add on to the CM voltage. A more precise OPA can lower these but not necessary.

    -Marcoo

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    If you feel your thread is resolved, please selected Answered.

    If you are using the TL431, check out the new TL431LI and its low Iq counterpart ATL431LI for improved system performance in a p2p package.

    Check out: Designing with the improved TL431LI for how to calculate worst case error on all '431 devices.

    Check out: Designing with the ATL431LI in Flyback Converters for tips and tricks on how to lower standby Iq to meet DoE and CoC regulations.

  • In reply to Marcoo Z:

    Hi Marcoo,

    as per your comment the following circuit will be ok,

    Thanks,

    Venkatesh P

  • In reply to Venkatesh P17:

    Hi Venkatesh,

    The increase in resistors and added capacitor are good. Is there a reason you eliminated the OPA? I believe the OPA is needed or else the voltage drop across R10 will add too much error. Add the OPA.

    -Marcoo

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    If you feel your thread is resolved, please selected Answered.

    If you are using the TL431, check out the new TL431LI and its low Iq counterpart ATL431LI for improved system performance in a p2p package.

    Check out: Designing with the improved TL431LI for how to calculate worst case error on all '431 devices.

    Check out: Designing with the ATL431LI in Flyback Converters for tips and tricks on how to lower standby Iq to meet DoE and CoC regulations.

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