The AMC7908EVM is connected to the computer through the on-board FTDI digital controller using the USB cable that is supplied with the EVM. The evaluation board features connectors and test points for all communication lines, DAC outputs, supplies, and the ADC inputs. Figure 3-1 shows a block diagram of the AMC7908EVM.

Figure 2-1 Theory of Operation Block Diagram

The USB connection provides the 5V supply to the EVM. A voltage regulator generates 3.3V from the USB 5V supply. These 5V and 3.3V supplies are used to power the FTDI controller.

The AMC7908 VDD supply can use the on-board 5V supply depending on the J13 pins 3-4 setting. By default, the VDD supply is connected to the on-board 5V supply. Alternatively, VDD can be supplied externally through banana jack J5. Remove the jumper connector on J13 pins 3-4 before connecting external supplies to VDD.

The AMC7908 VIO supply can use the on-board 3.3V supply depending on the J13 pins 1-2 setting. By default, the VIO supply is connected to the on-board 3.3V supply. Alternatively, VIO can be supplied externally through banana jack J8. Remove the jumper connector on J13 pins 1-2 before connecting external supplies to VIO.

The AMC7908 VCCA and VCCB supplies are used to configure the device to operate in the positive output range. If using the positive range, then power VCCA and VCCB externally using banana jacks J3 and J11, respectively. If using the negative range, then place a shunt on pins 1-2 of J2 and J9 to connect VCCA and VCCB to ground. Jumper J6 can be used to connect VCCA and VCCB together, allowing for the use of one external supply to power both VCCA and VCCB. Remove the jumper connections on pins 1-2 of J2 and J9 before connecting external supplies to VCCA or VCCB, respectively.

The AMC7908 VSSA and VSSB supplies are used to configure the device to operate in the negative output range. If using the negative range, then VSSA and VSSB can be powered externally using banana jacks J4 and J12, respectively. Alternatively, an on-board voltage regulator is available to provide negative voltage to the supplies. The regulator is powered by an external negative power supply, VNEG, and can output either –7 V or –10.5 V depending on the position of jumper J28. Jumper J29 connects the on-board negative voltage to the VSSA and VSSB supplies. If using the positive range, place a shunt on pins 2-3 of J2 and J9 to connect VSSA and VSSB to ground. Remove the jumper connections on J29 and pins 1-2 of J2/J9 before connecting external supplies to VSSA and VSSB.

There are multiple unpopulated components on the EVM that can be populated to change the configuration of the EVM:

• R7 and R9 are I²C pull-ups to VIO. When using a communication source other than the FTDI controller for I²C communication, R7 and R9 can be populated for pull-ups to VIO.
• C6, C11, C18, and C20 are 0603 footprints to allow for larger capacitance loads on the DACA1, DACA3, DACB1, and DACB3, respectively.
• J14, J15, J20, J21, J26, and J27 are optional terminal blocks. See Table 3-4 for more information.