MAXREFDES74#: 18-Bit, Analog Front End, ±5V in

The MAXREFDES74# reference design performs high-speed, 18-bit, precision data acquisition based on Maxim’s leading-edge, high-accuracy, low-power data converters. The MAXREFDES74# design works as a building block for a high-speed, low-power, high-accuracy data acquisition and control system for industrial process control and automation, and high-speed protection systems for power distribution and automation. (By changing the ADC and DAC to pin-compatible 16-bit devices such as the MAX11166 and the MAX5316, a 16-bit data acquisition system can also be tested.)

The analog front-end consists of two user-selectable MAX9632 op amps, followed by the MAX11156. The op amps can be configured as inverting or noninverting amplifiers by jumper selectors. Both op amps work as anti-aliasing lowpass filters (LPF) and can be daisy-chained to create a second-order LPF.

The output of the MAX5318 DAC can also be configured as a positive or negative single-ended output, or as a true differential output through three MAX9632 op amps. The DAC output can also be shifted up to double the output level to 2 x VREF.

The voltage reference (VREF) for both the ADC and DAC comes from the selectable reference sources, which include the MAX6126, with 3ppm/°C, 0.02% initial accuracy VREF in an 8-pin SO package, and the MAX6070, with 6ppm/°C, 0.04% initial accuracy VREF in a 6-pin SOT23 package. The MAX11156 can use an internal VREF (default operation) or one of the external references.