DEMO MANUAL DC1792A LTC2756 Serial 18-Bit SoftSpan I DAC OUT Description Demonstration circuit 1792A features the LTC2756 18-bit separate span control pins if SoftSpan operation is not SoftSpan, I DAC. The digital interface is a simple, needed. Voltage input offset and gain adjustment pins OUT 4-wire Serial Peripheral Interface (SPI) interface, aug- facilitate trimming of residual DC errors without impacting mented with separate CLEAR and LDAC pins that reset the excellent temperature stability of this device. the output to zero and load the DAC code, respectively. Design files for this circuit board are available at This device features six output ranges: 0V to 5V, 0V to DEMO MANUAL DC1792A Quick start proce D Additional software documentation may be available from V : Select source for 5V V supply. Set to 5V for sup- CC CC the Help menu item, as features may be added periodically. ply by onboard LTC6655 reference (recommended). Set to REG to be supplied by regulated supply from DC590 Controller and remove the jumper to supply externally. V : Select source for reference. Set to 5V to use onboard REF LTC6655 reference or select EXT to drive externally through the V jumper. REF CLR: Asynchronous Clear Input. Tie to 0 to set all DAC outputs to 0V. LDAC: Asynchronous DAC Load Input. Tie to 0 to update all DACS if CS is high. RFLAG: Reset Flag Output. Remove jumper and probe Figure 2. Software Screenshot middle pin for RFLAG status. HARDWARE SET-UP Analog Connections (Turret Posts) V : DAC Voltage Output. OUT Jumpers V : DAC Reference Voltage. If the onboard LTC6655 REF MSPAN: Manual Span Control Pin. MSPAN is used to reference is selected, the voltage may be measured at these configure the LTC2756 for operation in a single, fixed points. If a remote reference is selected, then an external output range. If MSPAN is 1 (high) it will be configured reference must be applied to these points. for single span use. If MSPAN is low it will be set through the QuikEval Software. Default position is 0 (low). VOSADJ: DAC offset adjust input, use only if VOSA jumper set to EXT. Nominal input range is 5V, which will provide S0, S1, S2: Used to set the fixed output range if MSPAN 2048LSB of offset adjustment. is 1 (high). GEADJ: Gain Adjust Pin. This voltage control pin can be Table 1. MSPAN Configuration used to null gain error or to compensate for reference S2 S1 S0 SPAN errors. The gain error change expressed in LSB is the 0 0 0 0V to 5V same for any output range. Nominal range is 5V, which 0 0 1 0V to 10V will provide 2048LSB of gain adjustment. 0 1 0 5V 0 1 1 10V Power and Ground Connections 1 0 0 2.5V + Analog Power: AMPV , AMPV , and GND turret posts 1 0 1 2.5V to 7.5V are the analog supplies for the onboard DAC amplifiers. These should be connected to a well regulated, low noise GEADJ: Gain Adjust Pin. If no adjustments are required, 15V power supply. select GND. Selecting EXT. connects the pin to the turret allowing external adjustment to null gain error or com- V : Connection to V . See schematic and description CC CC pensate for reference errors. for V jumper. CC VOSADJ: Offset Adjustment Selection for DAC. If no Grounding: Separate power and signal grounds are pro- offset adjustment is required, select GND. Selecting EXT vided. Signal GND is the turret closest to V , use this OUT connects the offset pin to the turret allowing external for measurement ground and output return. Power GND adjustment of offset. + is between AMPV and AMPV turrets. dc1792af 2 ure