Texas Instruments DAC7741EVM manual Host Processor Operation, Unity Gain Output Jumper Settings

Host Processor Operation

3.2 Host Processor Operation

The host processor basically drives the DAC, so the DACs proper operation depends on the successful configuration between the host processor and the EVM board. In addition, a properly written code is also required to operate the DAC.

A custom cable can be made specific to the host interface platform. The EVM allows interface to the host processor through J2 and J3 header connectors for the control signals, and J1 header connector for the data input. The output can be monitored through the J5 BNC connector (if installed) or J4 header connector. An interface adapter card is also available for specific DSP starter kits as mentioned in Chapter 1 of this manual.

The EVM includes an optional signal conditioning circuit for the DAC output through an external operational amplifier, U2. This is set to a unity gain configuration by default. Regardless, the raw output of the DAC can be probed through W13 pin 2 so that it can be compared with the output of U2 if necessary. The output terminals J5 and J4 are provided to monitor the desired output of the DAC by shorting the respective pins of W13.

The following sections describe the different configurations of the output amplifier, U2.

3.2.1Unity Gain Output

The buffered output configuration is used to prevent loading the DAC7741 and should closely match the raw output of the DAC with maybe some slight distortion because of the feedback resistor and capacitor. The user can tailor the feedback circuit to closely match their desired wave shape by simply desoldering R7 and C11 and replacing them with the desired values. You can also simply get rid of R7 and C11 altogether and just solder a zero-Ωresistor in replacement of R7, if desired.

Table 3-2 shows the jumper setting for the unity gain configuration of the DAC external output buffer in unipolar or bipolar mode.

Table 3-2. Unity Gain Output Jumper Settings

Reference	Jumper Setting		Function
	Unipolar	Bipolar
W5	2-3	1-2	Supplies the voltage for the negative rail of op-amp.
W12	2-3	1-2	Supplies the voltage for the positive rail of op-amp.
W13	3-4	3-4	DAC output is channeled to the output terminals.
W14	Open	Open	exREFin is disconnected from the negative input of op-amp.
W15	Open	Open	Disconnect negative input of op-amp from GND

EVM Operation 3-3