Datasheet

ADS803

SBAS074B

www.ti.com

FIGURE 12. Recommended Bypassing for Analog Supply Pins.

GROUNDING AND DECOUPLING

Proper grounding and bypassing, short lead length, and the

use of ground planes are particularly important for high-

frequency designs. Multi-layer PC boards are recommended

for best performance, since they offer distinct advantages

like minimizing ground impedance, separation of signal lay-

ers by ground layers, etc. It is recommended that the analog

and digital ground pins of the ADS803 be joined together at

the IC and be connected only to the analog ground of the

system.

The ADS803 has analog and digital supply pins, however,

the converter should be treated as an analog component and

all supply pins should be powered by the analog supply. This

will ensure the most consistent results, since digital supply

lines often carry high levels of noise that would otherwise be

coupled into the converter and degrade the achievable per-

formance.

Due to the pipeline architecture, the converter also generates

high-frequency current transients and noise that are fed back

into the supply and reference lines. This requires that the

supply and reference pins be sufficiently bypassed. Figure

12 shows the recommended decoupling scheme for the

GND

ADS803

0.1µF 0.1µF

GND

2.2µF

VDRV

0.1µF

+5V/+3V

+5V

analog supplies. In most cases, 0.1µF ceramic chip capaci-

tors are adequate to keep the impedance low over a wide

frequency range. Their effectiveness largely depends on the

proximity to the individual supply pin. Therefore, they should

be located as close to the supply pins as possible. In

addition, a larger size bipolar capacitor (1µF to 22µF) should

be placed on the PC board in close proximity to the converter

circuit.