AD7682 Analog Devices, AD7682 Datasheet - Page 23

• Manufacturer Part Number: AD7682
• Manufacturer: Analog Devices

Specifications of AD7682

• Resolution (bits): 16bit
• # Chan: 4
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Bip,SE-Uni
• Ain Range: Bip (Vref) x 0.5,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: CSP

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.
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
0.010
0.001
1000
75
70
65
60
55
50
45
40
35
30
100
0.1
10
1
1
10
Figure 35. Operating Currents vs. Sampling Rate
VDD = 5V, INTERNAL REF
VDD = 5V, EXTERNAL REF
100
Figure 34. PSRR vs. Frequency
10
SAMPLING RATE (SPS)
FREQUENCY (kHz)
1k
100
VDD = 2.5V, EXTERNAL REF
10k
VIO
1k
100k
10k
1M
Rev. C | Page 23 of 32
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:
•
•
•
1
5V
OPTIONAL REFERENCE BUFFER AND FILTER.
The system power supply directly
A reference voltage with enough current output capability,
such as the
A reference buffer, such as the AD8605, which can also
filter the system power supply, as shown in Figure 36
10kΩ
1µF
Figure 36. Example of an Application Circuit
5V
ADR43x/ADR44x
AD8605
1
10µF
5V
REF
10Ω
1µF
AD7682/AD7689
VDD
AD7689
0.1µF
VIO
0.1µF