EVAL-AD7689EDZ Datasheet, PDF (23/32 Pages) Analog Devices – 16-Bit, 4-Channel/8-Channel, 250 kSPS PulSAR ADC

Data Sheet
POWER SUPPLY
The AD7682/AD7689 use two power supply pins: an analog
and digital core supply (VDD) and a digital input/output inter-
face supply (VIO). VIO allows direct interface with any logic
between 1.8 V and VDD. To reduce the supplies needed, the
VIO and VDD pins can be tied together. The AD7682/AD7689
are independent of power supply sequencing between VIO and
VDD. Additionally, it is very insensitive to power supply varia-
tions over a wide frequency range, as shown in Figure 34.
75
70
65
60
55
50
45
40
35
30
1
10
100
1k
10k
FREQUENCY (kHz)
Figure 34. PSRR vs. Frequency
The AD7682/AD7689 power down automatically at the end of
each conversion phase; therefore, the operating currents and
power scale linearly with the sampling rate. This makes the part
ideal for low sampling rates (even of a few hertz) and low
battery-powered applications.
10,000
1000 VDD = 5V, INTERNAL REF
100
VDD = 5V, EXTERNAL REF
10
VDD = 2.5V, EXTERNAL REF
1
VIO
0.1
0.010
0.001
10
100
1k
10k
100k
1M
SAMPLING RATE (SPS)
Figure 35. Operating Currents vs. Sampling Rate
AD7682/AD7689
SUPPLYING THE ADC FROM THE REFERENCE
For simplified applications, the AD7682/AD7689, with their
low operating current, can be supplied directly using an
external reference circuit like the one shown in Figure 36. The
reference line can be driven by:
• The system power supply directly
• A reference voltage with enough current output capability,
such as the ADR43x/ADR44x
• A reference buffer, such as the AD8605, which can also
filter the system power supply, as shown in Figure 36
5V 10kΩ
1µF
5V
5V
AD8605 ^10µF
10Ω
1µF
0.1µF
0.1µF
1
REF
VDD
VIO
AD7689
1_{OPTIONAL REFERENCE BUFFER AND FILTER.}
Figure 36. Example of an Application Circuit
Rev. D | Page 23 of 32