ADS1299
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SBAS499A –JULY 2012–REVISED AUGUST 2012
QUICK-START GUIDE
PCB LAYOUT
Power Supplies and Grounding
The ADS1299 has 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, AVDD1
and AVSS1 are recommended to be star-connected to AVDD and AVSS. It is important to eliminate noise from
AVDD and AVDD1 that is non-synchronous with the ADS1299 operation. Each ADS1299 supply should be
bypassed with 10-μF and a 0.1-μF solid ceramic capacitors. Placement of the digital circuits [(such as digital
signal processors (DSPs), microcontrollers, and field-programmable gate arrays (FPGAs)] in the system is
recommenced to done such that the return currents on those devices do not cross the analog return path of the
ADS1299. The ADS1299 can be powered from unipolar or bipolar supplies.
The capacitors used for decoupling can be surface-mount, low-cost, low-profile multi-layer ceramic capacitors. 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 that a non-ferroelectric capacitor such as a tantalum or class
1 capacitor (for example, C0G or NPO) be installed. EIA class 2 and class 3 dielectrics (such as X7R, X5R, and
X8R) 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 (+5 V and +3.3 V) Supplies
Figure 53 illustrates the ADS1299 connected to a unipolar supply. In this example, analog supply (AVDD) is
referenced to analog ground (AVSS) and digital supply (DVDD) is referenced to digital ground (DGND).
+5 V
+3.3 V
0.1 mF
1 mF
1 mF
0.1 mF
AVDD AVDD1 DVDD
VREFP
VREFN
0.1 mF
10 mF
VCAP1
VCAP2
VCAP3
VCAP4
RESV1
Device
1 mF
1 mF
0.1 mF
1 mF
100 mF
AVSS1 AVSS DGND
NOTE: Place the capacitors for supply, reference, and VCAP1 to VCAP4 as close to the package as possible.
Figure 53. Single-Supply Operation
Copyright © 2012, Texas Instruments Incorporated
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