EVAL-CONTROLBRD AD [Analog Devices], EVAL-CONTROLBRD Datasheet - Page 15

• Manufacturer Part Number: EVAL-CONTROLBRD
• Description: 16-Bit, 1.33 MSPS PulSAR ADC in MSOP/QFN
• Manufacturer: AD [Analog Devices]

VOLTAGE REFERENCE INPUT
The AD7983 voltage reference input, REF, has a dynamic input
impedance and should therefore be driven by a low impedance
source with efficient decoupling between the REF and GND
pins, as explained in the Layout section.
When REF is driven by a very low impedance source, for example,
a reference buffer using the
chip capacitor is appropriate for optimum performance.
If an unbuffered reference voltage is used, the decoupling value
depends on the reference used. For instance, a 22 μF (X5R,
1206 size) ceramic chip capacitor is appropriate for optimum
performance using a low temperature drift
If desired, a reference-decoupling capacitor value as small as
2.2 μF can be used with a minimal impact on performance,
especially DNL.
Regardless, there is no need for an additional lower value ceramic
decoupling capacitor (for example, 100 nF) between the REF
and GND pins.
AD8031
or the AD8605, a ceramic
ADR43x
reference.
Rev. 0 | Page 15 of 24
POWER SUPPLY
The AD7983 uses two power supply pins: a core supply (VDD) and
a digital input/output interface supply (VIO). VIO allows direct
interface with any logic between 1.8 V and 5.0 V. To reduce the
number of supplies needed, VIO and VDD can be tied together.
The AD7983 is independent of power supply sequencing between
VIO and VDD. Additionally, it is very insensitive to power supply
variations over a wide frequency range, as shown in Figure 25.
To ensure optimum performance, VDD should be roughly half
of REF, the voltage reference input. For example, if REF is 5.0 V,
VDD should be set to 2.5 V (±5%).
80
75
70
65
60
55
1
Figure 25. PSRR vs. Frequency
10
FREQUENCY (kHz)
100
AD7983
1000