AD7322BRU View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
AD7322BRU Datasheet PDF : 18 Pages
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Preliminary Technical Data
VDD
Vin0
D
C1 D
R1 C2
VSS
Figure 10. Equivalent Analog Input Circuit-(Single Ended)
VDD
Vin+
D
C1 D
R1 C2
VSS
VDD
D
Vin-
C1 D
R1 C2
VSS
Figure 11. Equivalent Analog Input Circuit-(Differential)
Care should be taken to ensure the Analog Input never exceeds
the VDD and VSS supply rails by more than 300 mV. This will
cause the diodes to become forward biased and start
conducting into either the VDD or VSS rails. These diodes can
conduct up to 10 mA without causing irreversible damage to
the part.
The Capacitor C1, in Figure 10 and Figure 11 is typically 4 pF
and can primarily be attributed to pin capacitance. The resistor
R1, is a lumped component made up of the on-resistance of the
input multiplexer and the track-and-hold switch. The Capacitor
C2, is the sampling capacitor, its capacitance will vary
depending on the Analog input range selected.
Track-and-Hold Section
The Track-and-Hold on the Analog Input of the AD7322 allows
the ADC to accurately convert an input sine wave of full scale
amplitude to 13-Bit accuracy. The input bandwidth of the
Track-and-Hold is greater than the Nyquist rate of the ADC ,
the AD7322 can handle frequencies up to 13 MHz.
The Track-and-Hold enters its tracking mode on the 15th SCLK
falling edge after the CS falling edge. The time required to
acquire an input signal will depend on how quickly the
sampling capacitor is charged. With zero source impedance 300
ns will be sufficient to acquire the signal to the 13-bit level.
The acquisition time required is calculated using the following
formula:
tACQ = 10 x ((RSOURCE + R) C)
where C is the Sampling Capacitance and R is the resistance
AD7322
seen by the track-and-hold amplifier looking back on the input.
For the AD7322, the value of R will include the on-resistance of
the input multiplexer. The value of R is typically 300 Ω. RSOURCE
should include any extra source impedance on the Analog
input.
TYPICAL CONNECTION DIAGRAM
Figure 12 shows a typical connection diagram for the AD7322.
In this configuration the AGND pin is connected to the Analog
ground plane of the system. The DGND pin is connected to the
Digital ground plane of the system. The Analog Inputs on the
AD7322 can be configured to operate in Single Ended, True
Differential or Pseudo Differential Mode. The AD7322 can
operate with either the internal or an external reference. In
Figure 12, the AD7322 is configured to operate with the internal
2.5V reference. A 470 nF decoupling capacitor is required when
operating with the internal reference.
The VCC pin can be connected to either a 3V or a 5V supply
voltage. The VDD and VSS are the dual supplies for the high
voltage analog input structures. The voltage on these pins must
be equal to or greater than the highest analog input range
selected on the analog input channels, see Table 5 for more
information. The VDRIVE pin is connected to the supply voltage
of the microprocessor. The voltage applied to the VDRIVE input
controls the voltage at which the serial interface operates.
Figure 12. Typical Connection Diagram
Rev. PrE | Page 11 of 18
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