Utilizes 16-bit DAC to provide 40-channel output with programmable

Circuit Functionality and Benefits

This circuit uses a multichannel DAC configuration with different output ranges for each group of channels. It uses the AD5370 to provide 40 DAC channels with 16-bit resolution. The AD5370 is configured with 8 channels having ±10 V output ranges and the other 24 channels having −4 V to +8 V output ranges.

The AD5370 is the only 40-channel, 16-bit resolution DAC in the industry that offers these industrial signal level outputs and flexible multiple output ranges. Together with the XFET® family of low noise precision voltage references, it provides a solution that offers industry-leading DAC channel density, minimum size, flexibility, and performance.

Figure 1. Using the AD5370 DAC to Provide 40-Channel Outputs with Programmable Output Voltage Range (Simplified Schematic; Decoupling and All Connections Not Shown)

Circuit Description

The AD5370 is a 40-channel, 16-bit DAC available in 64-lead LFCSP and 64-lead LQFP packages. It has two reference voltage input pins. VREF0 is the reference voltage pin for DAC channels VOUT0 to VOUT7, and VREF1 is the reference voltage pin for DAC channels VOUT8 to VOUT39.

Figure 1 shows a typical configuration of the AD5370 using two external references. The nominal output range of the AD5370 is four times the reference voltage. The default offset DAC register value of the AD5370 allows an output range of −4 V to +8 V when using a 3 V reference. Programming the offset DAC registers associated with VOUT0 to VOUT7 provides an output range of ±10 V when using a 5 V reference. The ADR435 is a 5 V low noise precision reference. The ADR423 is a 3 V low noise precision reference. When connected as shown in Figure 1, the AD5370 will have an output range of ±10 V for VOUT0 to VOUT7 and an output range of −4 V to +8 V for VOUT8 to VOUT39. The AD5370 contains two offset DAC registers; these registers allow the midscale point of the output range to be adjusted within the limits of the device's capabilities and dynamic headroom. The default value of the offset DAC register is 5461 (0x1555), which results in a midscale point of 2 V if a 3 V reference is used. This results in an output range of −4 V to +8 V, which is the default output range for VOUT8 to VOUT39. If the offset DAC 0 register is set to 8192 (0x2000), the midscale point is 0 V, resulting in an output range of ±10 V for VOUT0 to VOUT7.

The AD5370 is very flexible, and systems with many different output ranges can be designed using the same parts in the bill of materials.

This circuit must be constructed on a multilayer circuit board with a large area ground plane. Proper layout, grounding, and decoupling techniques must be used to achieve optimum performance (see Tutorial MT-031 and Tutorial MT-101).

Common Variations

The AD5371 is a 40-channel, 14-bit version of the AD5370 that provides three reference input pins. The AD5372 and AD5373 are 16-bit and 14-bit, 32-channel versions of the AD5370, respectively.

The circuit described in this article can be used with any of these AD537x devices. Other reference sources can be used to provide different output ranges if desired. The ADR421 and ADR431 are both 2.5 V reference sources that can be used to provide ±5 V outputs.