Electronic Design
Integrated DC-DC Buck Converter Reduces 8-bit Power Requirements

Integrated DC-DC Buck Converter Reduces 8-bit Power Requirements

Small, 8-bit microcontrollers are often chosen for tasks because they are very power efficient. Often this efficiency is due to a combination of features. For example, lower voltage transistors using the latest silicon technology reduces the active power requirements of the system. Likewise, the ability to sleep and wake up efficiently is important for many embedded applications. This is also a reason this class of microcontrollers has variety of sleep modes. There are always tradeoffs when selecting a mode but the result can be systems that can run decades on a single battery. Often the life of the system exceeds the life of the battery.

Lower operating voltages are desirable because it lowers active power requirements but unfortunately the power supplied by a battery does not exactly match what a micro needs. A low drop out (LDO) voltage regulator is part of most system designs to address the issue but LDOs can be less efficient if the supply voltage is significantly higher than the LDO output. In these cases it is often best to go with a DC-DC converter.

Silicon Labs takes this approach with its latest crop of 8051-based micros by including an on-board DC-DC buck converter. The DC-DC buck converter is 85% efficien and the output of the converter is available externally. This is great for wireless solutions where the wireless transceiver chip is powered by the DC-DC buck converter (Fig. 1). It is a more efficient than solution than using LDOs especially if there are various voltage requirements.

Silicon Labs' takes this approach with its new Si102x/3x multichip package, EZRadioPRO sub-GHz wireless MCU. The solution can lower active power mode requirements by up to 40%. The C8051F96x (Fig. 2) is the 8051 micro alone.

The DC-DC buck converter has a programmable output voltage that is independent of internal 1.8V used by the micro. There is an internal LDO as well that is part of the power cicruitry. The converter runs even when the chip is in sleep mode. In this case the chip is using very little power but the external device can continue to run. The converter output is limited to 95mA or about 0.25W.

The DC-DC buck converter is only part of the C8051F96x's power management support. It also has selective clock gating to 5 independent peripheral clocks trees. These are enabled or disabled based on the peripherals being controlled. A typical peripheral tree includes the crypto, encoder, SPI interface. The chip also has hardware AES encryption and CRC with DMA support.

The Enhanced LCD controller is power efficient as well. It utilizes a charge distribution approach with segment LCD control. It essentially uses the charge from one segment to drive the next segment.

As noted, the Si102x/3x integrates Silicon Labs' EZRadioPRO sub-GHz transceiver into a single package. The transceiver sensitivity is 121 dBm with an output power of +20 dBm. It is continuously programmable from 240 to 960 MHz. It also has an itegrated high-performance power amplifier and low-noise amplifier. There is a built-in antenna diversity algorithm along with an integrated FIFO and packet handler.

Silicon Labs is taking a modular approach to development. The pico-board contains the microcontroller and it plugs into the F96x UDP Base Board (Fig. 3). The F96x UDP Base Board also plugs into an LCD display board.

Pricing for the C8051F96x starts at $2.41. The Si103x price starts at $3.27.

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