AD7896BR Analog Devices Inc, AD7896BR Datasheet - Page 12

• Manufacturer Part Number: AD7896BR
• Description: A/D Converter (A-D) IC
• Manufacturer: Analog Devices Inc

Specifications of AD7896BR

• Package/case: 8-SOIC
• Features: +2.7V To 5V, 12?Bit ADC In 8?Pin
• Interface Type: Serial
• Leaded Process Compatible: No
• Number Of Bits: 12
• Number Of Channels: 1
• Peak Reflow Compatible (260 C): No
• Rohs Status: RoHS non-compliant
• Sampling Rate (per Second): 100k
• Data Interface: Serial
• Number Of Converters: 1
• Power Dissipation (max): 10.8mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-AD7896CBZ - BOARD EVALUATION FOR AD7896CBZ
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD7896
Dynamic Performance (Mode 1 Only)
With a combined conversion and acquisition time of 9.5 µs, the
AD7896 is ideal for wide bandwidth signal processing applications.
These applications require information on the ADC’s effect on the
spectral content of the input signal. Signal-to-(noise + distortion),
total harmonic distortion, peak harmonic or spurious noise, and
intermodulation distortion are all specified. Figure 11 shows a
typical FFT plot of a 10 kHz, 0 V to 3.3 V input after being digi-
tized by the AD7896 operating at a 102.4 kHz sampling rate.
The signal-to-(noise + distortion) ratio is 71.5 dB and the total
harmonic distortion is –82.4 dB.
Effective Number of Bits
The formula for signal-to-(noise + distortion) ratio (see the
Terminology section) is related to the resolution or number of
bits in the converter. Rewriting the formula below gives a mea-
sure of performance expressed in effective number of bits (N)
where SNR is the signal-to-(noise + distortion) ratio.
The effective number of bits for a device can be calculated from
its measured signal-to-(noise + distortion) ratio. Figure 12
shows a typical plot of effective number of bits versus frequency
for the AD7896 from dc to f
is 102.4 kHz. The plot shows that the AD7896 converts an input
sine wave of 51.2 kHz to an effective numbers of bits of 11.25,
which equates to a signal-to-(noise + distortion) level of 69 dB.
–100
–120
–20
–40
–60
–80
–0
0
Figure 11. AD7896 FFT Plot
10240
N = (SNR 1.76)/6.02
20480
SAMPLING
FREQUENCY (Hz)
30720
/2. The sampling frequency
f
f
SNR = 71.54dB
THD = –82.43dB
SAMPLE
IN
= 10kHz
40960
= 102.4kHz
51200
–12–
Power Considerations
In the automatic power-down mode, the part can be operated
at a sample rate that is considerably less than 100 kHz. In this
case, the power consumption will be reduced and will depend
on the sample rate. Figure 13 shows a graph of the power con-
sumption versus sampling rates from 10 Hz to 1 kHz in the
automatic power-down mode. The conditions are 2.7 V supply,
25°C, serial clock frequency of 8.33 MHz, and the data was
read after conversion.
Figure 12. Effective Number of Bits vs. Frequency
Figure 13. Power vs. Sample Rate in Auto Power-
Down Mode
12.00
11.75
11.50
11.25
11.00
200
160
120
80
40
0
10
0
SAMPLING RATE IN Hz
INPUT FREQUENCY (kHz)
100
25.6
f
SCLK
= 8.33MHz
1000
REV. C
51.2