Designing power management ICs (PMICs) for smart building applications

Smart buildings transform our living and working environments through advanced technologies such as IoT, AI, and automation.

These buildings integrate various subsystems, including lighting, HVAC, security, and IoT devices, each with specific power requirements. Power Management Integrated Circuits (PMICs) play a crucial role at the core of these systems. PMICs manage power distribution, ensuring devices like sensors, actuators, and control systems receive reliable and efficient power. This article explores the design of PMICs for smart building applications, offering insights for design engineers and technical professionals.

The role of PMICs in smart buildings and their challenges:

PMICs control power flow by supplying multiple output voltages to match the needs of different smart devices. They improve energy efficiency with high-efficiency converters and low-power modes that help reduce energy use. For wireless devices, PMICs manage the battery to extend its life. They can also work with energy harvesting sources like solar or heat, allowing devices to run without regular maintenance. The key functions are included-

Energy efficiency and power conversion: Smart buildings utilize various power sources, such as the grid, solar, thermal, and kinetic energy. Devices in hard-to-reach areas, such as ceiling-mounted sensors, benefit from energy harvesting, which reduces the need for frequent battery changes and lowers maintenance costs. PMICs help cut energy use by using efficient DC-DC converters and low dropout regulators (LDOs) that minimize power loss. They also support low-power standby modes, which are essential for battery-powered devices.
Diverse power requirements and multiple output rails: Smart buildings incorporate numerous devices with varied power needs. Many sensors operate at 3.3v, with low current, actuators may require 12v with more current and communication modules often use 5v. PMICs must generate multiple power outputs with precise voltage control to run all these devices properly. Smart thermostats, lighting controls, and security cameras depend on specific power settings for reliable operation.
Battery management and power path management: Wireless, battery-powered devices, such as sensors, often operate in places where wiring is complex. Power management chips control how batteries charge and discharge, helping them last longer. PMICs can also switch power sources smoothly between batteries, harvested energy (like solar), and the device itself, keeping everything running without interruption. This functionality is essential for devices such as occupancy sensors that must work for years without anyone changing their batteries.
Energy harvesting integration: Some smart building applications utilize energy harvesting from solar, thermal, or kinetic energy to power devices, reducing dependence on batteries and mains power. PMICs must efficiently capture and store this energy, handling variable inputs and low power levels. This capability is also helpful for ceiling-mounted sensors or window-integrated devices, aligning with the needs of smart buildings for sustainable, maintenance-free operation.
Reliability, safety, and protection mechanisms: Critical systems in smart buildings, like security and fire alarms, need an uninterrupted power supply. PMICs must include robust safety features to safeguard against overvoltage, current, and overheating. They also manage backup batteries. Advanced PMICs have built-in temperature sensors to prevent hot spots in crowded equipment areas. These features keep systems reliable, which helps buildings stay safe and meet essential standards like LEED (Leadership in Energy and Environmental Design) or BREEAM (Building Research Establishment Environmental Assessment Method).
Scalability, integration, and communication: Smart buildings vary in scale from small offices to large commercial buildings, necessitating scalable power management solutions. PMICs should offer flexible designs with customizable features and communication interfaces for integration with Building Management Systems (BMS). This integration enables PMICs to report power status or consumption data to the BMS, allowing building-wide energy optimization.
Handling peak current demands and transient loads: Smart building devices, especially those with wireless communication, can have peak current demands during transmission. Technologies such as Zigbee, Z-Wave, or Bluetooth Low Energy (BLE) transceivers require stable power during these bursts. PMICs must supply these transient loads without voltage drops that could disrupt communication. Features like dynamic voltage scaling and load transient response optimization are essential. Some advanced PMICs offer “mode” settings that enable fast switching and real-time output adjustments, ensuring stable power for radio transceivers during high-current bursts.
Electromagnetic compatibility: In a building with numerous electronic devices, PMICs must not create electrical noise that could disrupt other devices. The best PMICs use special features like spread-spectrum clocking or shielded inductors to reduce interference. This is critical for maintaining the integrity of communication signals in dense IoT networks, where interference could disrupt building automation.

Design considerations for PMICs in smart building applications

Efficient power management is a prime concern in the continuously evolving world of electronics. The PMICs lie at the heart of this challenge, allowing granular control over power distribution, conversion, and regulation in various electronic devices.

Support for multiple input sources:

Smart buildings use different power sources, and PMICs manage them efficiently to ensure devices remain operational, even in hard-to-reach locations. Managing these diverse energy sources requires PMICs with specialized capabilities to handle varying inputs while maximizing energy extraction.

Wide input voltage range: PMICs should accommodate input voltages from ultra-low levels (e.g., 100mV for thermoelectric generators) to higher ranges (e.g., 5-20V for solar panels). For instance, the MAX20361 supports inputs as low as 225mV, enabling harvesting from solar sources.
Maximum power point tracking (MPPT): PMICS require 78 MPPT algorithms tailored to the source impedance to maximize energy extraction. Certain ICs, like MAX20361, employ proprietary MPPT for power levels from 15µW to 300mW and adjust dynamically to varying light conditions. Figure 1 shows how the MAX20361 regulates the source voltage (VSRC) to a fraction of the open-circuit voltage (VOC) during MPPT until a new VOC reading or update is received.
Input protection: Overvoltage protection (OVP) and reverse polarity protection are critical to prevent damage from fluctuating renewable inputs. A typical OVP threshold might be set at 110% of the maximum input voltage (e.g., 22V for a 20V solar input).
Switching architecture: A multi-input selector with priority logic (e.g., grid > solar > battery) ensures seamless transitions. This can be implemented using analogue comparators or digital control via an I2C interface.

Figure 1: V_SRC behaviour during maximum power point tracking

Efficient power conversion

Smart buildings require PMICs that convert power efficiently to maximize battery life and make the most of harvested energy. High-efficiency conversion ensures stable voltage delivery while minimizing energy losses across various operating conditions.

DC-DC converter efficiency: Buck, boost, or buck-boost converters should achieve efficiencies >90% at typical loads (10mA-500mA). For example, the PCA9420’s buck converters from NXP offer >90% efficiency at 3.3V output.
Low Dropout regulators (LDOs): For noise-sensitive loads like RF transceivers, LDOs should provide high PSRR (>60dBat 1kHz) and low output noise (<50µVRMS). For example, the NCP170 from Onsemi achieves 30µV RMS noise, making it a suitable replacement for previous references. Similarly, ROHM's BD71847AMWV, designed for smart factories, offers six DC/DC buck converters and six LDOs, ideal for smart building applications.
Switching frequency optimization: High switching frequencies (1- 3MHz) reduce inductor size but may lower efficiency due to switching losses. A compromise (e.g., 2MHz) balances size and efficiency, using synchronous rectification to minimize conduction losses.
Buck-Boost capability: This is essential for energy harvesting, where input voltages fluctuate (e.g., 0.5- 5V from solar). The LTC3130 from Analog Devices supports a 2.4V-25V input range with seamless buck-boost transitions.
Load transient response: PMICs must handle load transients (e.g., 100mA to 500mA in 1µs) with minimal overshoot (<50mV), requiring high loop bandwidth (>100kHz) and output capacitance (e.g., 22µF).

To know more about PMICs design considerations watch the below video:

Video: PMIC | Tech Explainer

Battery management and power path management

Wireless smart building devices rely on batteries, which need careful management to maximize their lifespan and ensure reliable operation. Power path management ensures uninterrupted operation by intelligently prioritizing power sources.

Charging profiles: PMICS that support Li-ion, LiFePO4, or thin-film batteries with precise constant-current/constant-voltage (CC/CV) charging offer programmable fast-charge current (5mA-150mA) and termination voltage (3.5V-4.4V). Figure 2 shows a Li-ion battery charger using the MAX17703 from Analog Devices, optimized for safely charging large Li-ion batteries with precise voltage regulation (4.2V) and high charge currents (up to 10A).
Battery protection: Overcharge protection (e.g., 4.25V threshold), deep-discharge protection (e.g., 2.5V cutoff), and short-circuit protection are essential. A typical overcurrent limit might be 1A with a 10µs response time.
Power path control: Dynamic power path management prioritizes harvested energy over the battery, using MOSFET switches for low loss (<50mΩ RDSon). For instance, the PCA9412A from NXP implements adaptive path control for seamless switching.
State-of-Charge (SoC) monitoring: Coulomb counting or voltage-based SoC estimation with <1% accuracy, often via an I2C interface, enables predictive maintenance. For example, STC3117 from STMicroelectronics delivers high SoC accuracy and supports both Li-ion and LiFePO4 batteries.
Supercapacitor support: For energy harvesting, PMICs should charge supercapacitors (e.g., 1F at 5V) for burst loads, with balancing circuits to prevent overvoltage.

Figure 2: Typical application circuit of MAX17703, 10a Li-Ion battery charger

Low-power modes and power sequencing

Smart building devices, especially sensors, spend significant time in sleep or standby modes to conserve energy. Proper power sequencing prevents damage and ensures system reliability during power-up and power-down cycles.

Ultra-low quiescent current: Sleep modes should consume <1µA, with shutdown currents <100nA. For an example STPMIC1 from STMicroelectronics achieves 0.4µA in sleep mode and 80nA in shutdown and PCA9450 from NXP achieves 0.5µA in sleep mode and 50nA in shutdown.
Dynamic mode switching: Fast transitions (<10µs) between active, sleep, and standby modes, triggered by GPIO or I2C commands. For an example MAX77655 supports <5µs, ideal for rapid response in sensors.
Power sequencing: Programmable startup and shutdown sequences for multiple rails (e.g., 3.3V MCU before 1.8V IO). A typical sequence might delay the second rail by 1 ms with <10mV overshoot.
Wake-up mechanisms: External interrupts or timers to exit sleep mode, with low-power comparators (<500nA) for voltage threshold detection.
Retention modes: Maintain critical memory states with minimal power (e.g., 1µA for SRAM retention at 1.2V).

Communication interfaces

Smart building systems need PMICs to communicate with central management systems to provide status updates and receive commands. These interfaces enable remote monitoring and optimization of power usage.

I²C/SPI support: High-speed I2C (400kHz) or SPI (10MHz) is used to program voltage rails, read status registers, and report faults. For example, the PF8100 from NXP has I2C at 400kHz (Fast-mode) and SPI at up to 10MHz. Figure 3 shows a buck regulator block diagram with an I²C interface, which allows external digital control and configuration of parameters like switching frequency, current limits, and phase settings.
Data telemetry: Monitor input/output voltages, currents, and temperatures with <1% accuracy, using ADCs with 12-bit resolution or better. MIC2800 from Microchip offers 12-bit ADC for voltage, current, and temperature monitoring, with <1% accuracy, via I2C registers.
Interrupt mechanisms: GPIO pins for fault alerts (e.g., overcurrent, thermal events), with programmable thresholds (e.g., 125°C for thermal shutdown).
Protocol robustness: Error detection (e.g., CRC) and bus arbitration to prevent communication failures in noisy environments.

Buck regulator block diagram with I2C interface feature

Figure 3: Buck regulator block diagram with I²C interface feature

Thermal management and protection

Smart building environments can expose devices to temperature extremes, which make thermal management crucial for PMIC reliability. Protection features prevent damage in adverse conditions.

Thermal shutdown: Automatic shutdown at high temperatures (e.g., 150°C) with hysteresis (20°C) to prevent oscillations. For example, the PCA9420 includes thermal protection at 140°C.
Temperature monitoring: Integrated sensors with ±1°C accuracy, reporting via I2C, for proactive thermal management.
Overcurrent Protection (OCP): Limits current to safe levels (e.g., 1A) with fast response (<1µs), using sense resistors or MOSFETs.
Overvoltage/Undervoltage Protection (OVP/UVP): OVP thresholds at 110% of nominal voltage (e.g., 5.5V for a 5V rail), UVP at 80% (e.g., 4V).
Soft-start and inrush control: Ramp-up times of 1-5ms to limit inrush currents (<500mA peak), reducing stress on components.

Conclusion

PMICs are essential for efficient and reliable smart building systems. They manage power for diverse devices, including sensors, actuators, and communication modules across lighting, HVAC, and security systems. PMICs also convert energy efficiently, regulate and monitor batteries, support low-power modes, interface with building control systems, and provide thermal and fault protection. These features boost energy efficiency, increase reliability, and support sustainability by harvesting energy and lowering maintenance. Buildings have become smarter, and well-designed PMICs will continue to drive innovation in creating responsive, intelligent environments.