Choosing Buck Converters and LDOs for Miniature Industrial Automation Equipment

Arief Hernadi

As the factory automation and control equipment market evolves, shipments of equipment with sensors such as field transmitters, machine vision and position sensors are increasing. As a result, the demand for feature-rich power integrated circuits (ICs) that could power these devices is also growing.

Figure 1 shows a block diagram of a temperature transmitter. The nonisolated power-supply subsystem (highlighted in red) consists of a low dropout regulator (LDO), a DC/DC converter or a power module. In an earlier technical article, “Powering tiny industrial automation control equipment with high-voltage modules: how to ensure reliability,” my colleague Akshay Mehta explained how to power miniature industrial automation control equipment with high-voltage modules. In this article, I’ll take a look at how to use buck converters and LDOs for the same purpose.

Figure 1 Temperature Transmitter Subsystem

High Input Voltage, Higher Stakes

There are a number of ways to regulate the input DC voltage in factory automation and control equipment. You can use an LDO, a DC/DC converter or a power module. LDOs such as the TPS7A47 are commonly used in sensor power supplies due to their simple design and ability to attenuate input noise and deliver a ripple-free output voltage. DC/DC converters are a good choice for applications operating at lower output voltages, higher input voltages or higher output currents. For example, the LMR36503 and LMR36506 DC/DC converters enable a low shutdown current specification of 1 µA and an operating quiescent current specification of 7 µA. For loads with low output currents – less than 20 mA – these performance specifications ensure higher efficiency for 4- to 20-mA loop applications. Figure 2 shows the efficiency and thermal performance of the LMR36506 converter.

Figure 2 Efficiency and Thermal Performance at 24 v_IN, 5 V_OUT, 2.1 Mhz at 0.6A

Big Challenge, Small Solution

TPSM265R1 LMR36503 LMR36506 _IN _OUT

Figure 3 LMR36506 Example Solution Size

Lowering EMI, Raising the Standard

Figure 4 An EMI Filter Structure for DC/DC Converters

LMR36503 LMR36506

Figure 5 Wire-bond Quad Flat No-lead and FCOL Packages

Conclusion

LMR36506

Additional Resources:

If you’re considering using modules to power your solution, read our technical article: Powering tiny industrial automation control equipment with high-voltage modules: how to ensure reliability

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