Figure 1-1 Simplified Block Diagram for Smart Thermostats

For the purpose of this report, a simplified smart thermostat system block diagram is used to illustrate the logic and translation use cases. See Smart Thermostats for a more complete view of the interactive online End Equipment Reference Diagram.

It is extremely common for smart thermostats to utilize wireless interfaces such as Wi-Fi™, ZigBee™, or Bluetooth™ to connect to a local network. In many designs, the simplest method to achieve this is to utilize pre-built and pre-approved modules. These modules often have limited voltage operation ranges, and to support their usage, voltage-level shifters are typically required between the extremely low power processor, often operating as low as 1.2 V, and the wireless module, commonly operating at 3.3 V.

The most common communication protocols used between the processor and wireless interface are SDIO and UART. Each is addressed specifically in the following sections.

Figure 2-1 Using Voltage Translation with an SD Card Communication Bus

• Enable communication when devices have mismatched logic voltage levels.
• Improve data rates over discrete translation solutions.
• Protect controller while SD Card is not connected.
• See online parametric search tool to find the right voltage level translator.