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ADS1299: ADS1299EVM

eli
Guru 13485 points
Part Number: ADS1299

We start using the ADS1299 EVB and have some question regarding the Bias.

KIT:  ads1299 demo kit SLAU443 – MAY 2012 (lit num SBAS499).

 

  1. For doing internal BIAS TEST as indicated :

It is not clear what should I expect to receive. No indicative picture. I understand BIASIN pin uses internal BIAS of 2.5v. (AVDD+AVSS)/2 = 2.5v. So should I get 0V?

I am getting about 0.5V. Could you clarify ?

 

  1. I am using 6V for supply. I can also use 6v batteries as shown in the manual

Normal Electrode Test with differential inputs centered around 0 volt requires bipolar supplies of +/-2.5V. Is this supply generated on the demo board and just need to set jumpers or I should connect somehow bipolar supply externally. Please clarify specifically.

 

  • 0
    TI__Guru 66176 points

    Hi Eli,

    Thanks for your post.

    The ADS1299EEGFE-PDK generates both a 5-V unipolar supply and a 5-V bipolar supply (+/- 2.5 V) on the daughterboard. Please see Figure 61 of the User Guide for the appropriate jumper configurations.

    The ADS1299 will generate an internal BIASREF voltage that is equal to mid-supply, regardless of the supply configuration selected above. An external BIASREF voltage can also be applied to the BIASREF pin (pin 60). Make sure you set the BIASREF_INT bit in the CONFIG3[3] register accordingly.

    When BIAS_MEAS = 1 and the MUXn[2:0] bits for a specific channel = 010, the signal present on the BIASIN pin is connected to that channel's positive input (INxP) and the voltage present on BIASREF is connected to that channel's negative input (INxN). On the EVM daughterboard, the BIAS amplifier output (BIASOUT) is shorted to BIASIN through JP1[2-3]. The resistor divider used to generate an external BIASREF voltage is not installed by default, so you must configure BIASREF_INT = 1 (use the internal mid-supply voltage). If your jumper and register settings are correct, you should measure [BIASOUT - BIASREF] x Gain on the channel you selected for BIAS measurement. The output for that channel should be centered around 0 V since the DC common-mode voltage will cancel. The intent is to measure the AC common-mode cancellation signal generated by the BIAS amplifier.


    Best Regards,