Texas Instruments DAC7741EVM manual Output Gain of Two, 3. Gain of Two Output Jumper Settings

Host Processor Operation

3.2.2Output Gain of Two

This configuration allows the DAC output with a gain of two, but is limited to the effective rails of the operational amplifier. When the DAC7741 is configured to operate in bipolar mode, the DAC output must be within the range of 12 VP- P or less. Anywhere above the range of 12 VP- P would clip the output of the op-amp. Likewise, when operating the DAC in unipolar mode, the DAC output must not exceed 6 VP- P.

Table 3-3 shows the proper jumper settings of the EVM for the 2⋅ gain output of the DAC.

Table 3-3. Gain of Two Output Jumper Settings

Reference	Jumper Setting	Function
W5	1-2 (Bipolar)	Negative rail of the op-amp tied to -15 V for bipolar operation or AGND
	2-3 (Unipolar)	for unipolar operation.
W12	1-2	Positive rail supply of the op-amp tied to 15 V
W13	3-4	Amplified output of DAC is channeled to the output terminals
W14	Open	Disconnect exREFin from negative input of op-amp
W15	Close	Configures op-amp for a 2⋅ gain output

3.2.3Capacitive Load Drive

Another output configuration option is to drive a wide range of capacitive load requirement. However, all op-amps under certain conditions may become unstable depending on the op-amp configuration, gain, and load value. These are just few factors that can affect op-amps stability performance and should be considered when implementing.

In unity gain, the OPA627 op-amp, U2, performs very well with very large capacitive loads. Increasing the gain enhances the amplifier’s ability to drive even more capacitance, and by adding a load resistor would even improve the capacitive load drive capability.

Table 3-4 shows the jumper setting configuration for a capacitive load drive.

Table 3-4. Capacitive Load Drive Output Jumper Settings

Reference	Jumper Setting	Function
W5	1-2 (Bipolar)	Negative rail of the op-amp tied to -15 V for bipolar operation or AGND
	2-3 (Unipolar)	for unipolar operation.
W12	1-2	Positive rail supply of the op-amp tied to 15 V
W13	5-6	Capacitive load drive output of DAC is channeled to the output terminals
W14	Open	Disconnect exREFin from negative input of op-amp
W15	Open	Disconnect R12 (see note)

Note: If there is a need to incrementally adjust the capacitive load output, replace R12 with a capacitor with the desired capaci-

tance value and CLOSE W15.

3-4