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ADS127L11: Negative voltage input without negative reference condition

Ryuuichi machida
Guru 11525 points
Part Number: ADS127L11

Hello,

I would like you to confirm about below.

* When user want to input -2.048V to 2.048V to ADC as single end signal without negative reference source, Is following configuration available ?

AVDD1 = AVDD2 = 2.5V
AVSS = -2.5V
DGND = 0V
VREFP = 2.048V
VREFN = 0V
VINP = -2.048 to 2.048V (0V center)
VINN = 0V
("INP_RNG" bit should be set to "2x input range").

If this setting is available, which point should user connect VREFN and VINN ?
(VREFN and VINN are just connected to analog ground ? )

BR,

  • +1
    TI__Mastermind 36290 points

    Hello Ryuuichi-san,

    The above configuration will work as intended.  However, the INP_RNG should be set to 1x input range.  The full scale input range of the ADS127L11 is +/-Vref with 1x input.  In the case of Vref=2.048V, the full scale input range will be +/-2.048V.

    The ADS127L11 has a differential input that can also be operated in pseudo-differential.  The proposed configuration is pseudo-differential, where the negative input is held at a fixed 0V DC level.  You can expect to get similar SNR performance verses a fully differential input configuration, but the THD will be degraded by about 15dB (-105dB verses a typical -120dB in fully differential).

    Also, you cannot use the reference pre-charge buffer in this case, since AVDD1-VREFP<0.7V.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Guru 11525 points

    Hello Nicholas-san,

    Thank you for your reply.
    >The full scale input range of the ADS127L11 is +/-Vref with 1x input.  In the case of Vref=2.048V, the full scale input range will be +/-2.048V.
    Thank you for your correction. Actually, my case was single end not differential.

    I will close this thread.

    BR,