ADS1294 datasheet(76/88 Pages) TI

76 / 88 page

ADS1298

AVDD

0.1 F

1 F

+3V

AVDD1

AVSS

AVSS1

DGND

DVDD

+1.8V

0.1 F

1 F

0.1 F

VREFP

VREFN

VCAP1

VCAP2

VCAP3

VCAP4

WCT

1nF

1 F

10 F

22 F

0.1 F

RESV1

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

www.ti.com

QUICK-START GUIDE

PCB LAYOUT

Power Supplies and Grounding

The ADS129x have three supplies: AVDD, AVDD1, and DVDD. Both AVDD and AVDD1 should be as quiet as

possible. AVDD1 provides the supply to the charge pump block and has transients at fCLK. Therefore, it is

recommended that AVDD1 and AVSS1 be star-connected to AVDD and AVSS. It is important to eliminate noise

from AVDD and AVDD1 that is non-synchronous with the ADS129x operation. Each supply of the ADS129x

should be bypassed with 1

μF and 0.1μF solid ceramic capacitors. It is recommended that placement of the digital

circuits (DSP, microcontrollers, FPGAs, etc.) in the system is done such that the return currents on those devices

do not cross the analog return path of the ADS129x. The ADS129x can be powered from unipolar or bipolar

supplies.

Capacitors used for decoupling can be of surface-mount, low-cost, low-profile, multi-layer ceramic type. In most

cases, the VCAP1 capacitor can also be a multi-layer ceramic, but in systems where the board is subjected to

high- or low-frequency vibration, it is recommend to install a non-ferroelectric capacitor such as a tantalum or

class 1 capacitor (C0G or NPO). EIA class 2 and class 3 dielectrics such as (X7R, X5R, X8R, etc.) are

ferroelectric. The piezoelectric property of these capacitors can appear as electrical noise coming from the

capacitor. When using internal reference, noise on the VCAP1 node results in performance degradation.

Connecting the Device to Unipolar (+3V/+1.8V) Supplies

Figure 73 illustrates the ADS129x connected to a unipolar supply. In this example, analog supply (AVDD) is

referenced to analog ground (AVSS) and digital supplies (DVDD) are referenced to digital ground (DGND).

NOTE: Place the capacitors for supply, reference, WCT, and VCAP1 to VCAP4 as close to the package as possible.

Figure 73. Single-Supply Operation

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Product Folder Link(s): ADS1294 ADS1294R ADS1296 ADS1296R ADS1298 ADS1298R

ADS1294 Datasheet(PDF) 76 Page - Texas Instruments

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