Datasheet

UG-236 Evaluation Board User Guide
Rev. 0 | Page 4 of 16
TEST CIRCUITS
The EVAL-AD5254SDZ incorporates several test circuits to
evaluate the AD5254 performance.
DAC
RDAC0 can be operated as a digital-to-analog converter (DAC),
as shown in Figure 2.
09579-002
W1_BUF
A1
RDAC0
AC + DC
VDD
A0
B0
BUF-W1
VSS
GND
DC
2
V
DD
– V
SS
V
DD
2
V
DD
– V
SS
V
SS
R34
R35
W0
W1
B1
Figure 2. DAC
Table 4 shows the options available for the voltage references.
Table 4. DAC Voltage References
Terminal Link Options Description
A0 A20 AC + DC
Connects Terminal A0 to
(V
DD
− V
SS
)/2
VDD Connects Terminal A0 to V
DD
W0 BUF-W1
Connects Terminal W0 to an
output buffer
B0 A21 DC
Connects Terminal B0 to
(V
DD
− V
SS
)/2
VSS Connects Terminal B0 to V
SS
GND
Connects Terminal B0 to
analog ground
The output voltage is defined in Equation 1.
256
)(
RDAC0
VVV
B0
A0
OUT

(1)
where:
RDAC0 is the code loaded in the RDAC0 register.
V
A0
is the voltage applied to the A0 terminal (A20 link).
V
B0
is the voltage applied to the B0 terminal (A21 link).
Using the R34 and R35 external resistors, you 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 A0 and B0
terminals and recalculate V
A0
and V
B0
in Equation 1.
AC Signal Attenuation
RDAC0 can be used to attenuate an ac signal, which must be
provided externally using the AC_INPUT connector, as shown
in Figure 3.
W1_BUF
A1
RDAC0
AC + DC
A
C_INPUT
AC
A0
B0
BUF-W1
GND
2
V
DD
–
V
SS
V
SS
R34
R35
W0
W1
B1
1µF
R36
0
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DC
VSS
2
V
DD
– V
SS
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
Voltage
Supply
Maximum
AC Signal
Amplitude
Link Options Conditions
Single V
DD
A20 AC + DC 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
A21 DC
Use in conjunction
with AC + DC link
GND All other conditions
Dual V
DD
/V
SS
A20 AC + DC
AC signal is outside
the voltage supply
rails due to the
dc offset voltage
DC offset voltage
≠ 0 V
1
AC All other conditions
A21 GND
Use in conjunction
with AC + DC link
VSS 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
0
log20)dB( (2)
where:
R
WB0
is the resistor between the W0 and B0 terminals.
R
W
is the wiper resistance.
R
END-TO-END
is the end-to-end resistance value.