Datasheet

ADS1198
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
100pF 1 Fm 1 Fm 1 Fm
10 Fm
22 Fm0.1 Fm
RESV1
ADS1194, ADS1196
ADS1198
www.ti.com SBAS471C –APRIL 2010– REVISED NOVEMBER 2011
QUICK-START GUIDE
PCB LAYOUT
Power Supplies and Grounding
The ADS1194/6/8 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 ADS1194/6/8 operation. Each supply of the
ADS1194/6/8 should be bypassed with 1μF and a 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 ADS1194/6/8. The ADS1194/6/8 can be
powered from unipolar or bipolar supplies.
The capacitors used for decoupling can be of the 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 (for example, 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 54 illustrates the ADS1194/6/8 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 54. Single-Supply Operation
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Product Folder Link(s): ADS1194 ADS1196 ADS1198