Datasheet

ADS1298
0.1 Fm1 Fm
AVDD AVDD1
0.1 Fm1 Fm
-1.5V
AVSSAVSS1
DGND
DVDD
+1.5V
+1.8V
0.1 Fm 1 Fm
VCAP1
VCAP2
VCAP3
0.1 Fm
VREFP
VREFN
10 Fm
VCAP4
WCT
1 Fm
1 Fm
1nF 1 Fm
-1.5V
22 Fm
0.1 Fm
RESV1
5kW
10pF
AVSS
AVDD
INxP,
INxN
ADS1294, ADS1294R
ADS1296, ADS1296R
ADS1298, ADS1298R
SBAS459I –JANUARY 2010–REVISED JANUARY 2012 www.ti.com
Connecting the Device to Bipolar (±1.5V/1.8V) Supplies
Figure 74 illustrates the ADS129x connected to a bipolar supply. In this example, the analog supplies connect to
the device analog supply (AVDD). This supply is referenced to the device analog return (AVSS), and the digital
supply (DVDD) is referenced to the device digital ground return (DGND).
NOTE: Place the capacitors for supply, reference, WCT, and VCAP1 to VCAP4 as close to the package as possible.
Figure 74. Bipolar Supply Operation
Shielding Analog Signal Paths
As with any precision circuit, careful PCB layout ensures the best performance. It is essential to make short,
direct interconnections and avoid stray wiring capacitance—particularly at the analog input pins and AVSS.
These analog input pins are high-impedance and extremely sensitive to extraneous noise. The AVSS pin should
be treated as a sensitive analog signal and connected directly to the supply ground with proper shielding.
Leakage currents between the PCB traces can exceed the input bias current of the ADS129x if shielding is not
implemented. Digital signals should be kept as far as possible from the analog input signals on the PCB.
Analog Input Structure
The analog input of the ADS129x is as shown in Figure 75.
Figure 75. Analog Input Protection Circuit
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