AD7694ARMZRL7 Datasheet, PDF (14/16 Pages) Analog Devices – 16-Bit, 250 kSPS PulSAR® ADC in MSOP

AD7694
Table 9. Recommended Driver Amplifiers
Amplifier
Typical Application
AD8021
Very low noise and high frequency
AD8022
Low noise and high frequency
OP184
Low power, low noise, and low frequency
AD8605, AD8615 5 V single-supply and low power
AD8519
Small, low power, and low frequency
AD8031
High frequency and low power
VOLTAGE REFERENCE INPUT
The AD7694 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, an unbuffered reference voltage like the low
temperature drift ADR43x reference or a reference buffer using
the AD8031 or the AD8605), a 10 μF (X5R, 0805 size) ceramic
chip capacitor is appropriate for optimum performance.
If desired, smaller reference decoupling capacitor values down
to 2.2 μF can be used with a minimal impact on performance,
especially DNL.
POWER SUPPLY
The AD7694 powers down automatically at the end of each
conversion phase and, therefore, the power scales linearly with
the sampling rate, as shown in Figure 22. This makes the part
ideal for a low sampling rate (even a few Hz) and low battery-
powered applications.
10,000
1,000
100
10
VDD = 5V
VDD = 2.7V
1
0.1
0.01
10
100
1k
10k
100k
1M
SAMPLING RATE (SPS)
Figure 22. Operating Current vs. Sampling Rate
SUPPLYING THE ADC FROM THE REFERENCE
For simplified applications, the AD7694, with its low operating
current, can be supplied directly using the reference circuit, as
shown in Figure 23. The reference line can be driven by either
• The system power supply directly
• A reference voltage with enough current output capability,
such as the ADR43x
• A reference buffer, such as the AD8031, that can also filter
the system power supply, as shown in Figure 23
5V OR 3V
5V OR 3V
5V 10kΩ
OR
3V
1μF
2.2
AD8031 TO
10μF
10Ω
1μF
(NOTE 1)
REF
VDD
AD7694
NOTES
1. OPTIONAL REFERENCE BUFFER AND FILTER.
Figure 23. Example of an Application Circuit
Rev. A | Page 14 of 16