Analog Devices EVAL-AD7492SDZ, Руководство пользователя

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UG-371 EVAL-AD7492SDZ User Guide
Rev. 0 | Page 6 of 24
AD7492
AD8597ARZ
R2
130
Ω
R5
51
Ω
LK15
C11
10µF
C2
0.1µF
R12
130
Ω
VDD_+5V
B
VIN
VIN
LK10
VIN_BIASED
A
VDD_–5V
UNIPOLAR
INPUT SIGNAL
SK1
VIN
C10
22pF
V+
V–
+
–
OP
6
7
U3
2
3
4
C16
0.1µF C8
10µF
10493-
003
Figure 3. Unipolar Input Buffer Circuitry
10493-
004
Figure 4. Bipolar Input Buffer Circuitry
ANALOG INPUTS
The analog input to the evaluation board can be either the SK1
SMB (push on) connector with a unipolar signal source or the
SK3 SMB (push on) connector when using a bipolar signal source.
The unipolar input is buffered with dedicated circuitry (U3)
and discrete components, as shown in Figure 3
.
LK15 can be used to put a 50 Ω impedance matching load on the
input. LK10 is placed in Position B to connect the output of U3
to the
AD7492 .
The bipolar signal is buffered with dedicated circuitry (U4, U6,
and U9) along with the discreet components shown in Figure 4.
The circuit shown in Figure 4 allows for different configurations,
and an external source can be applied to bias the input voltage.
The analog input buffer amplifier (U3) is set as a unity gain buffer.
The amplifier positive rail is driven from ±5 V (from
ADP1613,
U801, that is used to drive a dual rail, power supply, SEPIC Cuk
configuration), which can be changed to a different value, as
required, by using the external terminals on J800. LK801 and
LK802 must be set to Position B to drive the amplifiers from an
external source. For dynamic performance, an FFT test can be
done by applying a very low distortion ac source.
REFERENCE OPTIONS
The reference source can be from the AD7492 REF OUT pin or
the ADR431 ultralow noise XFET® voltage reference device (U5).
EXTERNAL CONNECTORS
Table 4 lists the connector functions of the evaluation board.
Table 4. Connector Functions
Connector Function
EXT_OFFSET SMB socket for external bias input, which
provided that LK20 is correctly configured, can
be applied to U6
J3 External VDRIVE screw terminal connector
J700 7 V to 9 V bench supply screw terminal connector
J702 7 V to 9 V dc transformer power connector
J703 AVCC screw terminal connector
J800 VSS and VDD screw terminal connectors
SK1 Unipolar signal input SMB socket
SK2
CONVST signal input SMB socket
SK3 Bipolar signal input SMB socket