Datasheet

ADS1298
AVDD
0.1 Fm1 Fm
+3V
AVDD1
AVSSAVSS1 DGND
DVDD
+1.8V
0.1 Fm 1 Fm
0.1 Fm
VREFP
VREFN
VCAP1
VCAP2
VCAP3
VCAP4
WCT
1nF 1 Fm 1 Fm 1 Fm
10 Fm
22 Fm0.1 Fm
RESV1
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
www.ti.com SBAS459I –JANUARY 2010–REVISED JANUARY 2012
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 f
CLK
. 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 1μF 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