Miniature Data Converters As systems get smaller and smaller, every square millimeter of printed circuit board (PCB) area counts. At the same time, as the demand for data increases, more sensors need to be monitored.

This article will discuss how to significantly reduce PCB footprint, increase channel density, and maximize the benefits of high integration of other components and functions with TI's tiny data converters to create more value in a smaller form factor.

The first advantage: the PCB takes up less space

And advances in packaging technology have made electronic components smaller and smaller.

As shown in Figure 1, TI's latest single-channel ADC (ADS7042) takes up 2.25mm2, almost half the size of comparable ADCs ten years ago. Likewise, TI's latest single-channel DAC (the DAC53401) is a quarter of the size of its class from a decade ago. Likewise, for multi-channel applications, TI's latest 8-channel ADC (ADS7138) and DAC (DAC53608) both have a footprint of 9mm2 (about 1mm2 per channel).

Figure 1: Smaller data converters from TI

These tiny data converters can reduce PCB size for space-constrained designs, or integrate more channels into the same PCB size, or both.

Advantage 2: Integrated analog function

Many systems use discrete and passive components to implement various analog functions such as signal conditioning, biasing, and comparators. Because TI's small data converters integrate these functions, they eliminate many discrete and passive components, reducing PCB size, simplifying design, and improving performance and reliability.

Some examples of such integrations include:

Fewer external components

As shown in Figure 2, the DAC53401 integrates an output buffer and an internal reference, saving PCB area and cost.

Figure 2: Integrated reference and buffer in the DAC53401

Another example is the ADS7138 shown in Figure 3. For most applications, the ADS7138 does not require a driver amplifier at the input, again saving PCB area and cost.

Figure 3: The ADS7138 does not require an external amplifier

· Bias voltage generation (fixed and variable)

The DAC53401's Electrically Erasable Programmable Read-Only Memory (EEPROM) and slew rate control features provide good conditions for generating fixed or variable bias voltages. Figure 4 shows an example of a lighting application.

Figure 4: DACx3401 Biasing LEDs

Analog and digital comparators

A comparator is often used in such systems because it immediately alerts the host controller when any critical signal such as current, voltage and temperature deviates from its expected range. This comparator should have a fast response time and be able to avoid false positives.

As shown in Figure 5, a separate feedback pin (FB) allows you to use the DAC53401 as an analog comparator with a programmable threshold voltage.

Figure 5: The DACx3401 has access to its internal amplifier feedback path

As shown in Figure 6, the ADS7138 integrates the digital comparator function with functions such as programmable thresholds, hysteresis, and event counters, greatly reducing the possibility of false positives.

Figure 6: ADS7138 as a digital comparator

Benefit 3: Integrated digital features

Smaller data converters allow not only remote sensor adjustments but also remote data processing. Local processing improves the performance of remote sensors, reduces response time in the event of an alarm, and frees up some processing bandwidth in the central processing unit.

Examples include:

Output averaging for improved noise performance

To reduce the effects of noise in a system, it is common practice to average sensor readings over a short period of time. As shown in Figure 7, the ADS7138 can average up to 128 samples, reducing the effects of noise by a factor of more than 10.

Figure 7: Average characteristics inside the ADS7138

· General purpose input/output (GPIO)

In many systems, detection of an alarm event requires immediate control action (such as turning off a heating element or turning on a hazard indicator). In the ADS7138, some analog input channels can monitor sensors, while unused analog input channels can be used as GPIO pins. As shown in Figure 8, the monitored sensor can control the state of the GPIO pins locally, or the state can be controlled remotely by a central processor using the I2C interface.

Figure 8: ADS7138: ADC and GPIO

Waveform generation

In some systems, you need to generate specific waveforms to generate beeps (as in medical applications) or to create LED breathing effects (as in lighting applications). DACs like the DAC53401 have a feature called continuous waveform generation that enables you to generate triangles, squares, trapezoids, or sawtooth waves, as shown in Figure 9.

Figure 9: DACx3401 generating multiple waveforms

Cyclic Redundancy Check (CRC)

Data integrity must be maintained when using ADCs such as the ADS7138 for critical monitoring functions or redundant measurements. As shown in Figure 10, the ADS7138 accomplishes this by performing a CRC on the data communication between the ADC and the central processing unit.

Figure 10: ADS7138 with CRC on input and output data

As shown in Figure 11, DACs such as the DAC53401 and DAC43401 use CRC to ensure that content written to or loaded from nonvolatile memory or EEPROM is not corrupted.

Figure 11: DACx3401 with CRC on NVM

Integrating these analog functions and digital features can lead to more complex integrated circuits, but it can greatly reduce overall system complexity by adding processing and diagnostic capabilities.