AD7854 Analog Devices, AD7854 Datasheet - Page 16

• Manufacturer Part Number: AD7854
• Description: 3 V to 5 V Single Supply, 200 kSPS, 12-Bit, Parallel Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7854

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Byte,Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (Vref) p-p
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

AD7854/AD7854L
REFERENCE SECTION
For specified performance, it is recommended that when using
an external reference, this reference should be between 2.3 V
and the analog supply AV
pins are shown below. If the internal reference is being used,
the REF
capacitor to AGND very close to the REF
connections are shown in Figure 16.
If the internal reference is required for use external to the ADC,
it should be buffered at the REF
capacitor should be connected from this pin to AGND. The typical
noise performance for the internal reference, with 5 V supplies is
150 nV/√Hz @ 1 kHz and dc noise is 100 µV p-p.
Figure 16. Relevant Connections Using Internal Reference
The REF
an external reference. This is possible due to the series resis-
tance from the REF
This external reference can be in the range 2.3 V to AV
When using AV
from the REF
possible to the REF
should be connected to AV
age as the reference. The connections for this arrangement are
shown in Figure 17. When using AV
add a resistor in series with the AV
of filtering the noise associated with the AV
Note that when using an external reference, the voltage present
at the REF
ence source resistance and the series resistance of 150 kΩ from
the REF
low source impedance external reference is recommended.
Figure 17. Relevant Connections, AV
+3V TO +5V
ANALOG
SUPPLY
+3V TO +5V
IN
IN
ANALOG
SUPPLY
IN
/REF
/REF
IN
/REF
10 F
/REF
IN
/REF
OUT
DD
OUT
OUT
10 F
0.01 F
OUT
0.1 F
0.1 F
as the reference source, the 10 nF capacitor
IN
IN
pin to the internal 2.5 V reference. Thus, a
pin should be decoupled with a 100 nF
pin may be overdriven by connecting it to
OUT
/REF
/REF
pin is determined by the external refer-
0.01 F
0.01 F
0.1 F
pin to AGND should be as close as
DD
0.1 F
0.1 F
OUT
OUT
DD
. The connections for the reference
C
C
REF
REF1
REF2
to keep this pin at the same volt-
pin, and also the C
pin to the internal reference.
IN
IN
/REF
C
C
REF
/REF
DD
REF1
REF2
AV
DD
AD7854L
IN
AD7854/
OUT
supply. This has the effect
DD
/REF
OUT
it may be necessary to
AV
DD
AD7854L
AD7854/
OUT
IN
DD
DV
DD
as the Reference
/REF
pin and a 100 nF
DD
supply.
DV
DD
OUT
REF1
0.1 F
pin. These
pin
DD
0.1 F
.
–16–
AD7854/AD7854L PERFORMANCE CURVES
Figure 18 shows a typical FFT plot for the AD7854 at 200 kHz
sample rate and 10 kHz input frequency.
Figure 19 shows the SNR versus frequency for different supplies
and different external references.
Figure 20 shows the power supply rejection ratio versus fre-
quency for the part. The power supply rejection ratio is defined
as the ratio of the power in ADC output at frequency f to the
power of a full-scale sine wave:
Pf = Power at frequency f in ADC output, Pfs = power of a full-
scale sine wave. Here a 100 mV peak-to-peak sine wave is
coupled onto the AV
unaltered. Both the 3.3 V and 5.0 V supply performances are
shown.
–100
–120
–20
–40
–60
–80
74
73
72
71
70
69
0
0
0
5.0V SUPPLIES, WITH 5V REFERENCE
Figure 19. SNR vs. Frequency
PSRR (dB) = 10 log (Pf/Pfs)
20
20
AV
DD
Figure 18. FFT Plot
DD
UNLESS STATED OTHERWISE
= DV
supply while the digital supply is left
INPUT FREQUENCY – kHz
FREQUENCY – kHz
DD
40
40
WITH 2.5V REFERENCE
3.3V SUPPLIES
5.0V SUPPLIES, L VERSION
AV
F
F
SNR = 72.04dB
THD = –88.43dB
SAMPLE
IN
60
60
DD
= 10kHz
= DV
5.0V SUPPLIES
= 200kHz
DD
= 3.3V
80
80
100
100
REV. B