Unlike other bipolar ADCs, the AD7366-5/AD7367-5 do not
have a resistive analog input structure. On the AD7366-5/
AD7366-5, the bipolar analog signal is sampled directly onto
the sampling capacitor. This gives the devices high analog input
impedance. The analog input impedance can be calculated from
the following formula:
Z = 1/(fS × CS)
fS is the sampling frequency.
CS is the sampling capacitor value.
CS depends on the analog input range chosen (see the Analog
Inputs section). When operating at 500 kSPS, the analog input
impedance is typically 260 kΩ for the ±10 V range. As the
sampling frequency is reduced, the analog input impedance
further increases. As the analog input impedance increases, the
current required to drive the analog input therefore, decreases
(see Figure 7 for more information).
TYPICAL CONNECTION DIAGRAM
Figure 20 shows a typical connection diagram for the AD7366-5/
AD7367-5. In this configuration, the AGND pin is connected
to the analog ground plane of the system, and the DGND pin
is connected to the digital ground plane of the system. The
analog inputs on the AD7366-5/AD7367-5 accept bipolar
single-ended signals. The AD7366-5/AD7367-5 can operate
with either an internal or an external reference. In Figure 20, the
AD7366-5/AD7367-5 is configured to operate with the internal
2.5 V reference. A 680 nF decoupling capacitor is required when
operating with the internal reference.
The AVCC and DVCC pins are connected to a 5 V supply voltage.
The VDD and VSS are the dual supplies for the high voltage analog
input structures. The voltage on these pins must be greater than
or equal to ±5 V (see Table 7 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 of the
serial interface. VDRIVE can be set to 3 V or 5 V.
+5V TO +16.5V
ANALOG INPUTS ±10V,
±5V, AND 0V TO +10V
VDD DVCC AVCC
+3V OR +5V SUPPLY
–16.5V TO –5V
Figure 20. Typical Connection Diagram for ±10 V Range Using Internal Reference
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