AD7328BRUZ Analog Devices Inc, AD7328BRUZ Datasheet - Page 20

• Manufacturer Part Number: AD7328BRUZ
• Description: IC ADC 12BIT+ SAR 8CHAN 20TSSOP
• Manufacturer: Analog Devices Inc

Specifications of AD7328BRUZ

• Data Interface: DSP, MICROWIRE™, QSPI™, Serial, SPI™
• Design Resources: Using AD7328 in Appls with Single-Ended Industrial-Level Signals (CN0047)
• Number Of Bits: 12
• Sampling Rate (per Second): 1M
• Number Of Converters: 1
• Power Dissipation (max): 30mW
• Voltage Supply Source: Dual ±
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP (0.173", 4.40mm Width)
• Resolution (bits): 13bit
• Sampling Rate: 1MSPS
• Input Channel Type: Pseudo Differential, Single Ended
• Supply Current: 900µA
• Digital Ic Case Style: TSSOP
• No. Of Pins: 20
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-AD7328CBZ - BOARD EVALUATION FOR AD7328
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

AD7328
DRIVER AMPLIFIER CHOICE
In applications where the harmonic distortion and signal-to-
noise ratio are critical specifications, the analog input of the
AD7328 should be driven from a low impedance source. Large
source impedances significantly affect the ac performance of the
ADC and can necessitate the use of an input buffer amplifier.
When no amplifier is used to drive the analog input, the source
impedance should be limited to low values. The maximum source
impedance depends on the amount of THD that can be tolerated
in the application. The THD increases as the source impedance
increases and performance degrades. Figure 21 and Figure 22
show graphs of the THD vs. the analog input frequency for various
source impedances. Depending on the input range and analog
input configuration selected, the AD7328 can handle source
impedances of up to 4.7 kΩ before the THD starts to degrade.
Due to the programmable nature of the analog inputs on the
AD7328, the choice of op amp used to drive the inputs is a
function of the particular application and depends on the input
configuration and the analog input voltage ranges selected.
–2
–4
–6
–8
–2
–4
–6
–8
8
6
4
2
0
4
2
0
Figure 40. Pseudo Differential Input Range with V
Figure 41. Pseudo Differential Input Range with V
V
V
V
V
CC
REF
CC
REF
= 5V
= 3V
= 2.5V
RANGE
RANGE
= 2.5V
±10V
±10V
±5V RANGE
±5V RANGE
±16.5V V
±16.5V V
RANGE
RANGE
±2.5V
±2.5V
DD
DD
0V TO +10V
0V TO +10V
/V
/V
RANGE
RANGE
SS
SS
RANGE
RANGE
±10V
±10V
±12V V
±12V V
±5V RANGE
±5V RANGE
DD
DD
/V
/V
SS
RANGE
SS
RANGE
±2.5V
±2.5V
0V TO +10V
0V TO +10V
RANGE
RANGE
CC
CC
= 5 V
= 3 V
Rev. B | Page 20 of 36
The driver amplifier must be able to settle for a full-scale step
to a 13-bit level, 0.0122%, in less than the specified acquisition
time of the AD7328. An op amp such as the AD8021 meets this
requirement when operating in single-ended mode. The
needs an external compensating NPO type of capacitor. The
AD8022
a dual version is required. For lower frequency applications, op
amps such as the AD797, AD845, and
the AD7328 in single-ended mode configuration.
Differential operation requires that V
neously driven with two signals of equal amplitude that are 180°
out of phase. The common mode must be set up externally to
the AD7328. The common-mode range is determined by the
REFIN/OUT voltage, the V
amplifier used to drive the analog inputs. Differential mode with
either an ac input or a dc input provides the best THD performance
over a wide frequency range. Because not all applications have a
signal preconditioned for differential operation, there is often a
need to perform a single-ended-to-differential conversion. This
single-ended-to-differential conversion can be performed using
an op amp pair. Typical connection diagrams for an op amp
pair are shown in Figure 42 and Figure 43. In Figure 42, the
common-mode signal is applied to the noninverting input of
the second amplifier.
Figure 43. Single-Ended-to-Differential Configuration with the AD8021
Figure 42. Single-Ended-to-Differential Configuration with the AD845
can also be used in high frequency applications where
V
IN
V
IN
100Ω
10kΩ
442Ω
1.5kΩ
1.5kΩ
2kΩ
CC
442Ω
442Ω
442Ω
442Ω
442Ω
supply voltage, and the particular
1.5kΩ
1.5kΩ
1.5kΩ
AD8021
AD8021
IN
AD8610
+ and V
V+
V–
V+
V–
IN
can be used with
− be simulta-
AD8021