AD7651 Analog Devices, AD7651 Datasheet - Page 19

• Manufacturer Part Number: AD7651
• Manufacturer: Analog Devices

Specifications of AD7651

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 100kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: Uni (Vref),Uni 2.5V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

POWER DISSIPATION VERSUS THROUGHPUT
Operating currents are very low during the acquisition phase,
allowing significant power savings when the conversion rate is
reduced (see
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.
CONVERSION CONTROL
Figure 26
process. The AD7651 is controlled by the CNVST signal, which
initiates conversion. Once initiated, it cannot be restarted or
aborted, even by the power-down input PD, until the conversion
is complete. CNVST operates independently of CS and RD .
Conversions can be automatically initiated with the AD7651. If
CNVST is held LOW when BUSY is LOW, the AD7651 controls
the acquisition phase and automatically initiates a new
conversion. By keeping CNVST LOW, the AD7651 keeps the
conversion process running by itself. It should be noted that the
analog input must be settled when BUSY goes LOW. Also, at
power-up, CNVST should be brought LOW once to initiate the
conversion process. In this mode, the AD7651 can run slightly
faster than the guaranteed 100 kSPS.
Although CNVST is a digital signal, it should be designed with
special care with fast, clean edges, and levels with minimum
overshoot and undershoot or ringing.
100000
10000
1000
100
10
shows the detailed timing diagrams of the conversion
10
Figure 25. Power Dissipation vs. Sampling Rate
Figure 25
). The AD7651 automatically reduces its
100
SAMPLING RATE (SPS)
1k
PDREF = PDBUF = PDHIGH
10k
02964-0-038
100k
Rev. 0 | Page 19 of 28
The CNVST trace should be shielded with ground and a low
value serial resistor (i.e., 50 Ω) termination should be added
close to the output of the component that drives this line.
For applications where SNR is critical, the CNVST signal should
have very low jitter. This may be achieved by using a dedicated
oscillator for CNVST generation, or to clock CNVST with a
high frequency, low jitter clock, as shown in
CS = RD = 0
CNVST
CNVST
MODE
BUSY
RESET
CNVST
BUSY
DATA
BUSY
DATA
BUS
Figure 28. Master Parallel Data Timing for Reading (Continuous Read)
ACQUIRE
t
t
3
5
t
3
Figure 26. Basic Conversion Timing
t
PREVIOUS CONVERSION DATA
CONVERT
1
Figure 27. RESET Timing
t
7
t
t
4
t
9
1
t
2
t
6
t
10
ACQUIRE
t
t
8
4
t
8
Figure 22
t
11
AD7651
.
NEW DATA
CONVERT
02964-0-011
02964-0-012
02964-0-011