AD7949 Analog Devices, AD7949 Datasheet - Page 20

• Manufacturer Part Number: AD7949
• Description: 14-Bit, 8-Channel, 250 kSPS PulSAR ADC
• Manufacturer: Analog Devices

Specifications of AD7949

• Resolution (bits): 14bit
• # Chan: 8
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Adc Architecture: SAR
• Pkg Type: CSP

AD7949
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.
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
0.010
0.001
1000
75
70
65
60
55
50
45
40
35
30
100
0.1
10
1
1
10
Figure 34. Operating Currents vs. Sampling Rate
VDD = 5V, INTERNAL REF
VDD = 5V, EXTERNAL REF
100
Figure 33. 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 20 of 32
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:
•
•
•
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 35
10kΩ
1µF
Figure 35. Example of an Application Circuit
5V
ADR43x
AD8605
1
or
10µF
ADR44x
5V
REF
10Ω
1µF
VDD
AD7949
0.1µF
Data Sheet
VIO
0.1µF