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ADS1294 Datasheet(PDF) 30 Page - Texas Instruments |
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ADS1294 Datasheet(HTML) 30 Page - Texas Instruments |
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30 / 88 page  22 F m ToADCReferenceInputs VCAP1 10 F m VREFP VREFN Bandgap 2.4Vor4V AVSS R1 (1) R3 (1) R2 (1) 100W 100kW 100W OPA211 10pF 0.1 F m +5V 0.1 F m 10 F m 100 F m 22 F m OUT VIN +5V TRIM 22 F m REF5025 ToVREFPPin ADS1294, ADS1294R ADS1296, ADS1296R ADS1298, ADS1298R SBAS459H – JANUARY 2010 – REVISED OCTOBER 2011 www.ti.com REFERENCE Figure 35 shows a simplified block diagram of the internal reference of the ADS129x. The reference voltage is generated with respect to AVSS. When using the internal voltage reference, connect VREFN to AVSS. (1) For VREF = 2.4V: R1 = 12.5kΩ, R2 = 25kΩ, and R3 = 25kΩ. For VREF = 4V: R1 = 10.5kΩ, R2 = 15kΩ, and R3 = 35kΩ. Figure 35. Internal Reference The external band-limiting capacitors determine the amount of reference noise contribution. For high-end ECG systems, the capacitor values should be chosen such that the bandwidth is limited to less than 10Hz, so that the reference noise does not dominate the system noise. When using a 3V analog supply, the internal reference must be set to 2.4V. In case of a 5V analog supply, the internal reference can be set to 4V by setting the VREF_4V bit in the CONFIG2 register. Alternatively, the internal reference buffer can be powered down and VREFP can be applied externally. Figure 36 shows a typical external reference drive circuitry. Power-down is controlled by the PD_REFBUF bit in the CONFIG3 register. By default the device wakes up in external reference mode. Figure 36. External Reference Driver 30 Submit Documentation Feedback Copyright © 2010–2011, Texas Instruments Incorporated Product Folder Link(s): ADS1294 ADS1294R ADS1296 ADS1296R ADS1298 ADS1298R |
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