Test Circuits - Analog Devices UG-397 User Manual

UG-397

TEST CIRCUITS

The EVAL-AD5247DBZ and EVAL-MB-LV-SDZ incorporate
several test circuits to evaluate the
DAC
RDAC can be operated as a digital-to-analog converter (DAC),
as shown in Figure 2.
AC+
V – V
DD SS
2
VDD
V
DD
R34
A1
RDAC
W1
A
W
B
B1
Figure 2. DAC
Table 4 shows the options available for the voltage references.
Table 4. DAC Voltage References
Link Link
1
Terminal (DB ) (MB
A1 A2-B A9
W1 A3-B BUF-
W1
B1 A10
A1
inserted
1 Daughter board
2
Motherboard
The output voltage is defined in Equation 1.
RDAC
 
V ( V )
OUT A
128
where:
RDAC is the code loaded in the RDAC register.
V is the voltage applied to the A terminal (A9 link).
A
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 in Equation 1.
A
AD5247 performance.
–
BUF-W1
VOUT1
+
2
) Options Description
AC+ Connects Terminal
A1 to V /2
DD
VDD Connects Terminal
A1 to V
DD
Connects Terminal
W1 to an output
buffer
AGND
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.
1kHz
HPF
AC_INPUT
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
A9 AC+
AC
A10 AGND
The signal attenuation is defined in Equation 2.
Attenuatio
where:
R is the resistor between the W and ground.
WB
R is the wiper resistance.
W
R is the end-to-end resistance value.
(1)
END-TO-END
Rev. 0 | Page 4 of 16
Evaluation Board User Guide
V – V
DD SS
2
AC+
AC
R34
A1
RDAC
W1
BUF-W1
A
W
B
B1
Figure 3. AC Signal Attenuator
Conditions
No dc offset voltage.
AC signal is outside the voltage supply rails
due to the dc offset voltage.
DC offset voltage ≠ V /2.
DD
All other conditions.
All other conditions.


R R

 
WB W
n ( dB ) 20 log

R

 
END TO END
–
VOUT1
+


(2)

