Datasheet
UG-391 Evaluation Board User Guide
Rev. 0 | Page 4 of 16
TEST CIRCUITS
The EVAL-AD5258DBZ and EVAL-MB-LV-SDZ incorporate
several test circuits to evaluate the performance of the AD5258.
DAC
The RDAC can be operated as a digital-to-analog converter
(DAC), as shown in Figure 2.
VOUT1
R34
R35
A1
W1
RDAC
A
B
W
VDD
V
DD
AC+
V
DD
–
V
SS
2
AGND
BIAS
V
DD
– V
SS
2
B1
BUF-W1
10619-002
Figure 2. DAC
Table 5 shows the options available for the voltage references.
The output voltage is defined in Equation 1.
64
)(
RDAC
VVV
B
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).
V
B
is the voltage applied to the B terminal (A10 link).
However, by using the R34 and R35 external resistors, the user
can reduce the voltage of the voltage references. In this case, use
the A1 and B1 test points to measure the voltage applied to the
A and B terminals and recalculate V
A
and V
B
in Equation 1.
AC Signal Attenuation
The 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
R35
A1
W1
RDAC
A
B
W
AC
AC+
V
DD
–
V
SS
2
AGND
BIAS
V
DD
– V
SS
2
B1
BUF-W1
AC_INPUT
1kHz
HPF
10619-003
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 4.
Table 4. 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
1
.
AC All other conditions.
A10 BIAS Use in conjunction with AC+ link
1
.
AGND All other conditions.
1
Recommended to ensure optimal total harmonic distortion (THD) performance.
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 B terminals.
R
W
is the wiper resistance.
R
END-TO-END
is the end-to-end resistance value.
Table 5. DAC Voltage References
Terminal Link (Daughter Board) Link (Motherboard) Options Description
A1 Switch B of A4 A9 AC+ Connects Terminal A1 to V
DD
/2
VDD Connects Terminal A1 to V
DD
W1 Switch B of A3 BUF-W1 Connects Terminal W1 to an output buffer
B1 Switch B of A2 A10 BIAS Connects Terminal B1 to V
DD
/2
AGND Connects Terminal B1 to analog ground
A1 inserted Closes feedback loop of second op amp in the AD8618