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ADS127L11: Requirement specification for REF under REFP precharge buffer On

Koshi Ninomiya
Expert 6225 points

Part Number: ADS127L11
Other Parts Discussed in Thread: REF54, OPA196, REF70

Tool/software:

Dear Team,

My customer is considering to use the ADS127L11 (High-speed mode) wtih the REF54410. And they are looking at REFP precharge buffer feature of the ADS127L11, because it is a new feature. When the REFP precharge buffer is On under High-speed mode, what specifications (bandwieth and etc.) are required for the REF?

The REF54 datasheet shows,

If linearlity, load regulation of the REF54410 is kept below 2ppm/mA, they think that the buffer OPA196 can be revmoved.

Best Regards,

Koshi Ninomiya

  • +1
    TI__Guru 52210 points

    Hello Koshi Ninomiya,

    Can you provide the name of the customer in the Notes section?

    The REFP buffer inside the ADS127L11 reduces the average reference load current from 500uA (Vref=2.5V) down to 2uA.  The REF54 can easily drive this average current, but there remains a small amount of high frequency current (average of 2uA).  Most of this high frequency current will be provided by the reference capacitors, but the AC response of the reference output will make a small difference.

    I have verified performance with the REF70 directly connected to the ADS127L11, and we get very good performance without any additional buffers.  It is very likely that the external amplifier is not needed with the REF54, but we do not have any data to verify this is the case. 

    If there is room on the customer board, I would suggest adding the buffer circuit as shown above, but provide a 0Ohm resistor to bypass the amplifier to verify performance with the amplifier and without.  Based on the measurement data, the customer can then easily decide if the additional amplifier is needed.

    Regards,
    Keith Nicholas
    Precision ADC Applications