Datasheet

EVM Stacking
3-4
3.3 EVM Stacking
Stacking the EVM is possible if there is a need to evaluate two DAC7654 to
yield a total of eight channel outputs. A maximum of two DAC7654 EVMs are
allowed because the output terminal, J4, dictates the number of DAC channels
that can be connected without the outputs colliding. Table 3−2 shows how the
DAC output channels are mapped into the output terminal, J4, with respect to
the jumper positions of W2, W3, W4, and W10.
Table 3−2.DAC7654 Output Channel Mapping
Reference Jumper Position Function
1−2 DAC7654 output A (V
OUT
A) is routed to J4−2.
W2
2−3 DAC7654 output A (V
OUT
A) is routed to J4−10.
1−2 DAC7654 output B (V
OUT
B) is routed to J4−4.
W3
2−3 DAC7654 output B (V
OUT
B) is routed to J4−12.
1−2 DAC7654 output C (V
OUT
C) is routed to J4−6.
W4
2−3 DAC7654 output C (V
OUT
C) is routed to J4−14.
1−2 DAC7654 output D (V
OUT
D) is routed to J4−8.
W10
2−3 DAC7654 output D (V
OUT
D) is routed to J4−16.
3.4 The Output Operational Amplifier
The EVM includes an optional signal-conditioning circuit for the DAC output
through an external operational amplifier, U2. Only one DAC output channel
can be monitored at any given time for evaluation because the odd-numbered
pins (J4−1 to J4−7) are tied together. The output operational amplifier is set to
unity gain configuration by default. Nevertheless, the raw outputs of the DAC
can be probed through the even pins of J4, the output terminal, which also
provides mechanical stability when stacking or plugging into any interface
card. In addition, it provides easy access for monitoring up to eight DAC
channels when stacking two DAC7654 EVMs together (see Section 3.3).
The inverting input of U2 can be tied to AGND (via W15) or the DAC output (by
shorting pins 1 and 2 of the J5 header) or to any voltage source through J5−1.
The following sections describe the different configurations of the output
amplifier, U2.
3.4.1 Unity Gain Output
The buffered output configuration is used to prevent loading the DAC, though it
may present some slight distortion because of the feedback resistor and
capacitor. The user can tailor the feedback circuit to closely match the desired
wave shape by removing R6 and C12 and replacing them with the desired
values. If desired, the user can remove R6 and C12 and solder a 0-Ω resistor in
replacement of R6.
Table 3−3 shows the jumper setting for the unity gain configuration of the
DAC external output buffer in unipolar or bipolar supply mode.