Datasheet

UG-397 Evaluation Board User Guide
Rev. 0 | Page 4 of 16
TEST CIRCUITS
The EVAL-AD5247DBZ and EVAL-MB-LV-SDZ incorporate
several test circuits to evaluate the AD5247 performance.
DAC
RDAC can be operated as a digital-to-analog converter (DAC),
as shown in Figure 2.
VOUT1
R34
RDAC
AC+
A
B
W
BUF-W1
+
–
A1
B1
W1
V
DD
– V
SS
V
DD
VDD
2
10625-002
Figure 2. DAC
Table 4 shows the options available for the voltage references.
Table 4. DAC Voltage References
Terminal
Link
(DB
1
)
Link
(MB
2
) Options Description
A1 A2-B A9 AC+
Connects Terminal
A1 to V
DD
/2
VDD
Connects Terminal
A1 to V
DD
W1 A3-B
BUF-
W1
Connects Terminal
W1 to an output
buffer
B1 A10 AGND
A1
inserted
1
Daughter board
2
Motherboard
The output voltage is defined in Equation 1.
128
)(
RDAC
VV
A
OUT

(1)
where:
RDAC is the code loaded in the RDAC register.
V
A
is the voltage applied to the A terminal (A9 link).
However, by using the R34 external resistor, the user can reduce
the voltage of the voltage references. In this case, use the A1 test
point to measure the voltage applied to the A terminal and
recalculate V
A
in Equation 1.
AC Signal Attenuation
RDAC can be used to attenuate an ac signal, which must be
provided externally using the AC_INPUT connector, as shown
in Figure 3.
VOUT1
R34
RDAC
AC+
AC
A
B
W
BUF-W1
+
–
A
C_INPUT
A1
B1
W1
V
DD
–
V
SS
2
HPF
1kHz
10625-003
Figure 3. AC Signal Attenuator
Depending on the voltage supply rails and the dc offset voltage
of the ac signal, various configurations can be used as described
in Table 5.
Table 5. AC Signal Attenuation Link Options
Link Options Conditions
A9 AC+ No dc offset voltage.
AC signal is outside the voltage supply rails
due to the dc offset voltage.
DC offset voltage ≠ V
DD
/2.
AC All other conditions.
A10 AGND All other conditions.
The signal attenuation is defined in Equation 2.










 ENDTOEND
WWB
R
RR
nAttenuatio log20)dB(
(2)
where:
R
WB
is the resistor between the W and ground.
R
W
is the wiper resistance.
R
END-TO-END
is the end-to-end resistance value.