AD7667 Analog Devices, AD7667 Datasheet - Page 20

• Manufacturer Part Number: AD7667
• Manufacturer: Analog Devices

Specifications of AD7667

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 1MSPS
• Interface: Par,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p,2.5V p-p,Uni (Vref),Uni 2.5V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

AD7667
For applications that use multiple AD7667s, it is more effective
to use the internal buffer to buffer the reference voltage.
Care should be taken with the voltage reference’s temperature
coefficient, which directly affects the full-scale accuracy if this
parameter matters. For instance, a ±15 ppm/°C temperature
coefficient of the reference changes full scale by ±1 LSB/°C.
Note that V
input range is defined in terms of V
increase the range to 0 V to 3 V with an AVDD above 4.85 V.
The AD780 can be selected with a 3 V reference voltage.
The TEMP pin, which measures the temperature of the
AD7667, can be used as shown in Figure 30. The output of
TEMP pin is applied to one of the inputs of the analog switch
(e.g., ADG779), and the ADC itself is used to measure its own
temperature. This configuration is very useful for improving the
calibration accuracy over the temperature range.
Power Supply
The AD7667 uses three power supply pins: an analog 5 V supply
AVDD, a digital 5 V core supply DVDD, and a digital input/
output interface supply OVDD. OVDD allows direct interface
with any logic between 2.7 V and DVDD + 0.3 V. To reduce the
supplies needed, the digital core (DVDD) can be supplied
through a simple RC filter from the analog supply, as shown in
Figure 26. The AD7667 is independent of power supply
sequencing once OVDD does not exceed DVDD by more than
0.3 V, and is thus free of supply voltage induced latch-up.
Additionally, it is very insensitive to power supply variations
over a wide frequency range, as shown in Figure 31, which
represents PSRR over frequency with on chip and external
references.
ANALOG INPUT
(UNIPOLAR)
Figure 30. Temperature Sensor Connection Diagram
REF
ADG779
can be increased to AVDD – 1.85 V. Since the
AD8021
C
C
IN
REF
, this would essentially
TEMP
AD7667
TEMPERATURE
SENSOR
Rev. 0 | Page 20 of 28
POWER DISSIPATION VERSUS THROUGHPUT
When using the Impulse mode of operation (IMPULSE =
HIGH, WARP = LOW), operating currents are very low during
the acquisition phase, allowing significant power savings when
the conversion rate is reduced (see Figure 32). The AD7667
automatically reduces its power consumption at the end of each
conversion phase. This makes the part ideal for very low power
battery applications. The digital interface and the reference
remain active even during the acquisition phase. To reduce
operating digital supply currents even further, digital inputs
need to be driven close to the power supply rails (i.e., DVDD or
DGND), and OVDD should not exceed DVDD by more than
0.3 V.
100k
10k
100
80
75
70
65
60
55
50
45
40
35
30
1M
1k
10
1
10
WARP MODE POWER
Figure 32. Power Dissipation vs. Sampling Rate
100
IMPULSE MODE POWER
INT REF
10
Figure 31. PSRR vs. Frequency
SAMPLING RATE (SPS)
FREQUENCY (kHz)
1k
100
EXT REF
10k
PDREF = PDBUF = HIGH
1000
100k
10000
1M