Many precision instruments, industrial automation, medical equipment, and automated test equipment applications require high-accuracy digital-to-analog conversion. Linear Technology has introduced the LTC2757, an 18-bit digital-to-analog converter (DAC) that provides ±1LSB INL (maximum) ) and ±1LSB DNL (maximum) accurate DC specifications.
The LTC2757 is an 18-bit multiplying parallel input, current output digital-to-analog converter that provides full 18-bit performance over a temperature range (±1LSB INL and DNL maximum) without any adjustments. All performance levels guarantee 18-bit monotonicity. The SoftSpanTM DAC operates from a single 3V to 5V supply and offers six output ranges that can be set via a parallel interface (up to ±10V) or pin-bonded to operate in one output range.
In addition to its precise DC specifications, the LTC2757 offers better AC specifications, including 2.1μs full-scale settling time (to 1LSB) and 1.4nV-s interference pulses.
The LTC2757 uses a bidirectional input/output parallel interface to enable readback of any on-chip registers, including the DAC output range setpoint, and a CLR pin and power-on reset circuit resets the DAC output to 0V. This is independent of the output range.
Figure 1 Typical application of LTC2757 
Figure 2 LTC2757 Reference PCB (1)
LTC2757 main features
- Maximum 18-bit INL error, ±1LSB over temperature
- 6 output ranges can be provided by programming or pin lap: 0V~5V, 0V~10V, -2.5V~7.5V, ±2.5V, ±5V, ±10V
- Monotonic throughout the temperature range
- Low interference pulse: 1.4nV-s (3V), 3nV-s (5V)
- 18-bit settling time: 2.1μs
- 2.7V~5.5V single power operation
- All coded constant reference currents
- Voltage controlled offset and gain trimming
- Parallel interface with all register readback functions
- Clear to 0V or power-on reset to 0V (this is independent of the output range)
- 48-pin 7mm & TImes; 7mm LQFP package
Figure 3 LTC2757 reference schematic 
Figure 4 LTC2757 reference PCB (2)
LTC2757A program features
The 1485A demo circuit uses the LTC2757A single 18-bit SoftSpan IOUT DAC with ±1LSB maximum INL. The device features six programmable output ranges: 0V~5V, 0V~10V, ±5V, ±10V, ±2.5V, -2.5 V~7.5V. This demo circuit can perform all LTC2757 functions, including system level gain and offset adjustment. The software automatically sets the LTC2757 output according to the login of the control panel. The square wave option can be used to test settling time (settling TIme). If software span control is required, the MSPAN jumper should be in a lower position. In addition, help menu items may also provide additional software documentation for periodic additions.
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