Datasheet

UG-396 Evaluation Board User Guide
Rev. 0 | Page 4 of 16
TEST CIRCUITS
The EVAL-AD5246DBZ and EVAL-MB-LV-SDZ incorporate
several test circuits to evaluate the AD5246 performance.
Antilogarithmic DAC
RDAC can be operated as a antilogarithmic DAC, as shown in
Figure 2. R35 should be replaced from the populated value of
0 Ω to the suggested value of 1.5 kΩ.
VOUT1
EXTERNAL
CONNECTION
R34
RDAC
AC+
A
B
W
BUF-W1
+
–
A1
B1
W1
V
DD
– V
SS
V
DD
VDD
2
R35
BIAS
V
DD
– V
SS
AGND
2
10624-002
Figure 2. DAC
The output voltage plot is shown in Figure 3. The output voltage
is relative to V
A
and V
B
.
1.0
0.8
0.6
0.4
0.2
0
0 20406080100120
DECIMAL CODE
REL
A
TIVE OUTPUT VOLTAGE
10624-003
Figure 3. Antilogarithmic Gain
Table 4 shows the options available for the voltage references.
Table 4. DAC Voltage References
Terminal
Link
(DB
1
)
Link
(MB
2
) Options Description
B A2-B A9 AC+
Connects
Terminal A1 to
V
DD
/2
VDD
Connects
Terminal A1 to
V
DD
W A3-B BUF-W1
Connects
Terminal W1
to an output
buffer
R35 A10 BIAS
Connects
Terminal B1 to
V
DD
/2
AGND
Connects
Terminal B1 to
analog
ground
A1
inserted
1
Daughter board
2
Motherboard
The output voltage is defined in Equation 1.
WB
B
A
OUT
RR
R
VVV


35
35
)( (1)
k10
128

RDAC
R
WB
where:
RDAC is 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 external resistor, the user can reduce
the voltage of the voltage reference. In this case, use the A1 test
point to measure the voltage applied to the A terminal and
recalculate V
A
in Equation 1.