AN-1215: 40 Channels of Programmable Industrial Level Output Span Using the AD5370 16-Bit Voltage Output DAC

Circuit Function And Benefits

This circuit is a multichannel DAC configuration with different output spans on groups of channels. It utilizes the AD5370 to provide 40 DAC channels with 16 bits of resolution. The AD5370 is configured to have eight channels with an output span of ±10 V and 24 channels with an output span of −4 V to +8 V

The AD5370 is the industry’s only 40-channel DAC offering these industrial signal level outputs and the flexibility of multiple output spans with 16-bit resolution. Coupled with the XFET® series of low noise precision references, the total solution represents industry-leading DAC channel density, smallest footprint, flexibility, and performance.

Circuit Description

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

Figure 1 shows a typical configuration for the AD5370 using two external references. The nominal output span for the AD5370 is four times the reference voltage. The default offset DAC register values for the AD5370 allow for an output span of −4 V to +8 V using a 3 V reference. Programming the offset DAC register associated with VOUT0 to VOUT7 allows a span of ±10 V to be achieved using a 5 V reference. The ADR435 is a low noise precision 5 V reference. The ADR423 is a low noise precision 3 V reference. When connected as shown in Figure 1, the AD5370 will have an output span of ±10 V on VOUT0 to VOUT7 and an output span of −4 V to +8 V on VOUT8 to VOUT39. The AD5370 has two offset DAC registers, which allow the mid-scale point of the span to be adjusted within the limits of part functionality and headroom. The default value of the offset DAC registers is 5461 (0x1555) giving a mid-scale point of 2 V when using a 3 V reference. This gives an output span of −4 V to +8 V and is the default for VOUT8 to VOUT39. Programming the offset DAC 0 register with 8192 (0x2000) sets the mid-scale point to 0 V. This gives output spans of ±10 V on VOUT0 to VOUT7.

The flexibility of the AD5370 allows systems to be designed with multiple different output ranges, with the same components on the bill of materials.

The circuit must be constructed on a multilayer PC 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 with three reference input pins. The AD5372 and AD5373 are 16-bit and 14-bit, 32 channel versions of the AD5370.

The circuit described here can be used with any of the AD537x devices mentioned. The references can also be changed to give different output ranges if required. The ADR421 and ADR431 are 2.5 V references, which can be used to create a ±5 V output.

References

Kester, Walt. 2005. The Data Conversion Handbook. Analog Devices. Chapters 3 and 7.

MT-015 Tutorial, Basic DAC Architectures II: Binary DACs. Analog Devices.

MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of AGND and DGND. Analog Devices.

MT-101 Tutorial, Decoupling Techniques. Analog Devices.

Voltage Reference Wizard Design Tool.