RSL10: Ultra-Low-Power Bluetooth

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For IoT edge-node devices or “connected” health and wellness applications, designers must consider at least the following parameters when comparing system power consumption levels between Bluetooth low energy radio SoCs:

  • Power Conversion: Most Bluetooth low energy radio SoCs operate at wide input voltage levels to satisfy the needs of different batteries. However, the battery voltage is most often different from the operating voltage of the Bluetooth low energy RF path as well as the operating voltage of on-chip Flash, processing cores, and memory. Hence, effective on-chip power conversion becomes important to get to the lowest possible power consumption.
  • Duty-cycling: Receiving (Rx) and Transmitting (Tx) currents are obviously important for the power budget; however, the paradox of most Bluetooth low energy applications is that most of the time they aren’t actually doing anything. Sampling, transmission and reception of data typically happens at very low data rates, which is why the sleep current of the device often becomes the dominant factor in the application’s overall power budget.

In response to the rapidly evolving needs of IoT and “connected” health and wellness applications, ON Semiconductor has the RSL10, a multi-protocol Bluetooth®5 certified radio SoC, offering the industry’s lowest power.

For RSL10, its defining “ultra-low-power” characteristic begins in applications that are typically battery powered (e.g., devices using 1.5 V AAA batteries, 3 V 2032 coin cells, 1.25 V 10A ZnAir batteries), and where the data throughput during normal operation is relatively low.

The Bluetooth low energy RF path of RSL10 operates “natively” at 1.1 V but, to ensure that battery voltages ranging from 1.1 V up to 3.6 V can be accommodated, RSL10 facilitates effective, on-chip DC/DC conversion as well as regulation to feed other parts of the system with appropriate voltages.

For instance, if the RSL10 is powered by a 3 V 2032 coin cell (which would be the case in many medical or remote sensing IoT applications), the following Sleep Mode currents can be achieved:

  • 25 nA with wake-up from external pin.
  • 40 nA with wake-up from external pin or internal timer.
  • 100 nA with wake-up from external pin or internal timer and 8 kB RAM retention.

Most alternative Bluetooth low energy radio SoCs require two to three times the amount of current to maintain similar modes.

Additionally, RSL10 draws 3.4 mA in Rx Mode and 4.6mA in Tx Mode – in both cases these numbers are achievable using the 2 Mbps data rate established by the new Bluetooth 5 standard.

So how do these numbers apply in a real world scenario where an application developer needs to calculate battery life time based on knowledge about the duty cycling of the application?

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