EVAL-AD7949EDZ View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-AD7949EDZ' PDF : 32 Pages View PDF
Data Sheet
POWER SUPPLY
The AD7949 uses two power supply pins: an analog and digital
core supply (VDD) and a digital input/output interface 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 AD7949 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 33.
75
70
65
60
55
50
45
40
35
30
1
10
100
1k
10k
FREQUENCY (kHz)
Figure 33. PSRR vs. Frequency
The AD7949 powers 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 34. Operating Currents vs. Sampling Rate
AD7949
SUPPLYING THE ADC FROM THE REFERENCE
For simplified applications, the AD7949, with its low operating
current, can be supplied directly using an external reference
circuit like the one shown in Figure 35. The reference line can
be driven by:
The system power supply directly
A reference voltage with enough current output capability,
such as the ADR430/ADR431/ADR433/ADR434/ADR435
or ADR440/ADR441/ADR443/ADR444/ADR445
A reference buffer, such as the AD8605, which can also
filter the system power supply, as shown in Figure 35
5V 10kΩ
1µF
5V
5V
AD8605 10µF
10Ω
1µF
0.1µF
0.1µF
1
REF
VDD
VIO
AD7949
1OPTIONAL REFERENCE BUFFER AND FILTER.
Figure 35. Example of an Application Circuit
Rev. F | Page 21 of 32
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