Because of the Thanksgiving holiday in the U.S., TI E2E design support forum responses may be delayed the week of Nov. 21. Thank you for your patience.

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS127L11: Negative voltage input without negative reference condition

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,

  • 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

  • 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,