Designing a low-power embedded product starts with careful component selection from the very beginning. Choosing energy-efficient components, arranging them to minimize energy consumption, and configuring them properly all play a role in the final power budget.

In this topic, we will look at the common components found in a typical Bluetooth LE product and understand how each one affects power consumption. A key point to remember: idle current matters just as much as active current. A Bluetooth LE device spends most of its time sleeping, so even small amounts of current drawn during idle periods can easily add up quickly and can dominate your power budget. Knowing the current draw of each component, both when active and when idle, will help us estimate the overall power budget across different operating modes.

1. Wireless SoC

At the core of every Bluetooth LE device is a wireless SoC that provides both the computational processing capabilities and the radio. The wireless SoC plays a crucial role in the device’s overall power consumption.

You can think of the wireless SoC as a microcontroller + a 2.4 GHz radio. The microcontroller provides the CPU and commonly used peripherals, such as UART and ADC. The rule of thumb here is to select an SoC that offers the lowest CPU processing current, the lowest TX and RX current when the radio is transmitting or receiving, and the lowest power consumption in sleep mode. Below are the numbers for the nRF54L15 SoC:

A key rule for achieving low power, which we will explore in lesson 4, is to configure the Wireless SoC so the 2.4 GHz radio (RX/TX) is ON as infrequently as possible and the CPU is asleep as frequently as possible.

2. Sensors and actuators

Bluetooth LE devices often include sensors and actuators. The sensor or actuator type depends on the device’s application. Typical sensors in a Bluetooth device include:

• Environmental: Temperature, humidity, pressure, air quality
• Motion: Accelerometer, gyroscope, magnetometer (IMU).
• Biometric: Heart rate, SpO2, ECG, Glucose Oxidase (GOx).
• Light: Ambient light sensors, UV sensors.
• Audio: MEMS microphones.

Typical actuators found in a Bluetooth device include:

• Haptic: Vibration motors.
• Audio: Buzzers, speakers.
• Mechanical: Servo motors, small relays.

When aiming for low-power design, it is important to select sensors and actuators that not only have low active current, but also, it is extremely important for them to have low sleep current. As low-power Bluetooth LE devices should be idle 95-99% of the time.

Here are the top guidelines when selecting/configuring sensors

• Prioritize sleep/standby current. Bluetooth LE devices spend 95%+ time sleeping.
• Use asynchronous (interrupt-driven) sensor operations when applicable (Wireless SoC sleep until data ready).
  • Avoid fragmented wakeups: Aim to batch sensor events so the system wakes up fewer times. A single long sleep is far more energy‑efficient than many short sleeps, because each wakeup carries additional power overhead.
• Avoid activating actuators or sensors during radio TX/RX to prevent high current peaks that reduce battery life. High current peaks with long duration, drastically impact battery capacity.
• Use sensors and actuators with operating voltage ranges matching the battery voltage or device PMIC output to avoid needing extra components, or extra voltage rails.
• Use lowest acceptable sampling rate for sensors.
• Use power-saving schemes implemented by the sensor.
• If the device has multiple sensors, group them in a separate power domain on the PCB with dedicated switches to shut off completely when unused.
• Consider the values of the pull-up and pull-down resistors for sensors.

Below are typical power consumption values for low-power accelerometer sensors to provide perspective on their current use:

The current numbers vary depending on the type of accelerometer used, especially in terms of accuracy, resolution, bandwidth, and advanced features included.

3. User interface

The user interface type selected for a Bluetooth LE device significantly affects its power budget. Some interface devices, such as push buttons, consume low power. When the button is inactive, it draws zero current (As we mentioned before, this current dominates the device’s operating time). When activated, it draws a small current equal to the input voltage divided by the GPIO pull-up resistance. The active current occurs rarely during the device’s lifetime(only when the button is pressed). The table below shows the current of a push button connected as an active low push button through the nRF54L15 14 kΩ Pull-up resistor:

When we compare mechanical push buttons with capacitive touch buttons, capacitive touch buttons require continuous current even when not being activated. This is fundamentally different from mechanical push buttons. Meaning this is a current that will always be consumed regardless of the device mode of operation.

From a power consumption perspective, the mechanical push button is more efficient than the capacitive touch button because it draws no current when idle, which accounts for 95-99% of the device’s operating time.

Now let us see what happens if the device includes a display. A single LED turned on can consume as much power as the entire wireless SoC when its radio is active.

Incorporating a display into your product drastically increases the power budget and significantly influences battery selection, as most displays introduce both high inactive and active current that depends on size and resolution. The exception is E-Paper displays, which consume zero inactive current even when displaying static content, and only consume current when updating the display content; however, their low refresh rate suits static content only or content that change infrequently. Below are rough estimates of power consumption for small-size common display technologies:

*Same value because power depends on content brightness, not whether it is changing

** depends on matrix size

In another context, How much current does it cost to keep showing something on a display?

E-Paper ▏ 0 µA
Segmented LCD ▎ 1-3 µA
Memory LCD ▍ 5-10 µA
|─────────── µA/mA boundary ───────────|
PMOLED ████ 8-20 mA
LED Matrix ██████ 20-80 mA
AMOLED ████████ 30-100 mA
TFT LCD ██████████ 40-100 mA

Remember: a single LED can draw 5 mA to 20 mA, equal to or exceeding the entire wireless SoC’s current during radio transmission.

Keeping an indication LED on, even with a low blinking frequency, during device sleep significantly increases power consumption and drains the battery. Therefore, it’s highly recommended to turn any indication LED off when the device is in sleep mode.

4. PCB, passives, and 2.4 GHz antenna

The PCB layout, RF passive components, and antenna design all affect both the power consumption and wireless range of a Bluetooth LE device. A key factor connecting these elements is impedance matching, ensuring that power flows efficiently between the radio, PCB trace, and the 2.4 GHz antenna.

Why impedance matching matters:
When impedance is mismatched, part of the transmitted signal reflects back instead of radiating from the antenna. This reflected power (measured as return loss) reduces the effective radiated power, which means:

• Shorter wireless range.
• The potential need to increase TX power to compensate(which leads to higher current).
• Longer transmission times to deliver the same data.

RF passive components (capacitors and inductors) form the matching network that transforms the radio and antenna impedance to match the 50 Ω RF trace. Low-quality passives introduce losses that waste energy as heat, reducing overall efficiency.

Antenna design is equally critical. The antenna’s physical size, placement on the PCB, and the ground plane dimensions determine its resonance frequency and radiation efficiency. Poor antenna design may require additional tuning components or result in reduced range – forcing higher TX power to compensate.

For each Wireless SoC in the nRF54L Series, Nordic Semiconductor provides reference circuitry for each production package (QFN48, CSP98, etc.). Use the PCB layouts and component values from these reference designs to ensure optimal RF performance. Below are the Nordic reference designs for the nRF54L15 SoC, QFN48 package.

PCB quality also plays a role in power consumption. A poorly manufactured PCB can have low-impedance paths between power and ground caused by solder flux residue, contamination, or poor etching quality. These defects create leakage currents that continuously drain the battery, even when the device is in sleep mode. This is especially problematic for low-power designs where sleep current is measured in microamps, a few microamps of PCB leakage can significantly impact battery life.

In summary, a good RF design maximizes the power that actually leaves the antenna, reducing the need for higher TX power. Combined with a high-quality PCB, this minimizes wasted energy and extends battery life.

5. Power source

Once you understand your device’s estimated power budget (covered in next topics) and its peak current requirements, you can select a battery for your product. At this stage, you also decide whether the design will use a rechargeable battery or a primary (non-rechargeable) cell. By combining these factors, you can then choose the most suitable battery type and determine the required capacity in milliamp-hours (mAh).

Below are common batteries used for Bluetooth LE devices.

Primary (Non-rechargeable) Cells:

Rechargeable:

The recommended voltage for the wireless SoC (1.7 – 3.6 V) for optimal efficiency is covered in the PMIC lesson .

6. Power management IC (PMIC)

A Power Management IC (PMIC) may be necessary when the battery voltage does not directly match the requirements of the components in your design. Common scenarios include:

• The battery voltage exceeds the SoC’s maximum input voltage.
• The battery voltage falls below the SoC’s minimum operating voltage as it discharges.
• Multiple voltage rails are required.

Or if the device requires advanced features such as:

• Battery charging (Li-Ion/Li-Po)
• Fuel gauging (both for rechargeable battery & primary cells)
• Load switches for components
• Support for hibernation/ship modes

A PMIC provides regulators, including linear LDO and switching (DCDC) types. A PMIC bridges the gap between your battery and your system’s power requirements. For simple designs with coin cell batteries operating within the SoC’s voltage range, a PMIC may not be necessary. However, for rechargeable batteries, multi-rail systems, or designs requiring advanced power features, a PMIC simplifies the design while improving efficiency, safety, and battery life monitoring.

Prioritize choosing a PMIC with regulators that have low quiescent current and high efficiency across the operating voltage and expected load to minimize power loss.

Switching regulators convert between voltage and current, and power is (mostly) conserved between the input and output. They efficiently accommodate a wide range of supply voltages and can provide either higher (boost) or lower (buck) output voltages relative to the input voltage.

Switching regulator efficiency varies slightly based on load current, input voltage, and output voltage. Typical values are η ≈ 80-95%.

Linear regulators, including LDOs, regulate voltage by acting like a variable resistor that adjusts resistance to maintain a fixed output voltage, with charge mostly conserved between input and output. They are simple and affordable, produce low noise, and have low quiescent current. However, the output voltage must be lower than the input voltage, efficiency is directly limited by the dropout voltage η = V_out/V_in, and excess energy is dissipated as heat proportional to the current due to the voltage drop.

Key comparisons

Example Comparison

Scenario: V_in = 3.7 V (Li-Ion), V_out = 1.8 V, I_out = 10 mA

Switching regulator- Buck (η = 90%):

P_in = 18 mW / 0.90 = 20 mW

P_loss = 2 mW

LDO

η_LDO = 1.8V / 3.7V = 48.6%

P_in = 3.7V × 10 mA = 37 mW

P_out = 1.8V × 10 mA = 18 mW

P_loss = 19mW (wasted as heat!). 17 mW more wasted compared to the buck regulator

When to Use Each

Use Switching regulator when:

• Large voltage difference (V_in >> V_out)
• Higher load currents (I_out > 1 mA)
• Battery life is critical!

Use LDO when:

• V_in ≈ V_out (small voltage drop, high efficiency)
• Very low I_out (I_q dominates)
• Extremely noise-sensitive applications

Nordic provides a comprehensive range of highly efficient PMICs designed for wireless SoCs. See table below: