Look at the details when designing an industrial PC – 1% is not always 1%

With process geometries of semiconductor technology declining to 10nm or below, designing the power supply for an industrial PC or single-board computer gets challenging like never before. In addition, the Industrial Internet of Things (IIoT) and Industry 4.0 are creating a stronger push toward smaller computing systems with increased performance. Figure 1 shows examples of supply requirements for some selected FPGAs with very low core voltages and very tight tolerances.

Figure 1: Supply voltage requirements for selected FPGAs (source: FPGA datasheets) 

Processors, field-programmable gate arrays (FPGAs) or system on chips (SoC)/application-specific integrated circuits (ASICs) using ultra-small process geometries offer very high functional integration and extreme performance levels, but they also require very high accuracy on their power-supply rails. Designing for 1.0V core voltages and below requires careful calculations of all DC specifications, as well as AC transients of corner spreads and process variations, to avoid false resets, unreliable operation or malfunction in single-board computer or industrial PCs.

Using 0.1% resistors to set the output voltage and adding multiple output capacitors can help fulfill the typical ±5% supply accuracy requirement even at very low voltages. But these resistors add cost and take up board space. Choosing a power supply with a 1% feedback voltage accuracy specification gives you more flexibility and potential cost reductions when selecting the output-voltage-setting resistor divider and output capacitors.

Figure 2 shows an example of the tolerance stack-up with a 1% reference voltage and 1% resistor accuracy, summing up to ±1.8% DC variations.

Figure 2: Target specification with 5% variation at a 1.0V core supply (source: Texas Instruments)


But you need to look at the details: not all 1% accuracy specifications are equal. Temperature variations and dependency on input voltages are common variables whose influences are sometimes not included in the 1% value. Some semiconductor suppliers show 1% accuracy on the first page of the data sheet. But this critical electrical parameter is often defined only at one given temperature and one input voltage point (for example, a 25°C room temperature and 3.6V input voltage).

TI’s new low-power TPS62147/TPS62148/TPS62135/TPS62136 (for 12V supply rails) and TPS62821/TPS62822/TPS62823/TPS62825/TPS62826 (for 5V supply rails) DC/DC buck converters can help solve the challenges that come with a 1% feedback voltage accuracy (or an output-voltage accuracy for fixed output-voltage options) specified over the full junction temperature range from -40°C to +125°C and over the full input voltage range of 3V to 17V or 2.4V to 5.5V. As well, these DC/DC converters are specified at very high output accuracy and offer very small solution size; for example: 1.5x1.5mm QFN for 2A or 3A (5V supply), or 2x3mm QFN for 2A or 4A (up to 17V supply).

For more information, visit TI’s new Power Management for FPGAs and Processors web page.

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