Mobile devices play an essential role in an increasingly connected and technological world. Mobile devices, as well as battery-powered gadgets, require multiple power rails and multiple power domains. A power management solution based on discrete components adds complexity to the design, involves higher costs and requires more PCB space. Integrating multiple voltage regulators and control circuits into a single chip, power management ICs (PMICs) represent a ready-to-use option for implementing a complete power supply solution.
PMIC features
PMICs perform several tasks, such as regulating voltage levels for different types of loads; controlling power startup and shutdown sequences; managing battery charging and discharging; and monitoring power usage. They also safeguard against voltage, current and temperature fluctuations.
A PMIC integrates several components. These include switching DC/DC voltage converters, low-dropout linear voltage regulators (LDOs), undervoltage protection circuitry, battery charging and status management circuitry, thermal management systems, switches for enabling or disabling loads, GPIOs and more. The regulated voltages available at the outputs of the PMIC are also called channels, so this device is more properly called a multi-channel PMIC.
Switching DC/DC converters can be buck (step-down), boost (step-up) or a combination. However, the buck type is more common for mobile applications, as the components that are powered generally require lower voltages than the lithium-ion battery powering the device.
Switching converters can achieve very high efficiency levels, typically above 90%. By raising the switching frequency, switching losses are significantly reduced. However, they introduce electromagnetic noise that can disturb the operation of sensitive high-integration components found in mobile devices.
To overcome this drawback, LDO voltage regulators are used. Operating with a small difference between output and input voltages, LDOs brilliantly overcome the problem of low efficiency typical in linear regulators (the greater the difference between output voltage and input voltage, the lower the efficiency). The advantages of LDOs include negligible noise, compact size (they do not require inductors) and circuit simplicity.
One example is Renesas Electronics Corp.’s DA9070, a PMIC with a high level of integration and configurability. It has a low quiescent current (Iq) and is designed for use in low-power battery applications, particularly wearable devices. The PMIC (Figure 1) consists of a linear charger that includes power path management, an ultra-low-Iq buck regulator, LDO/load switches, a broad output voltage boost regulator, an analog battery monitor, a watchdog and protective features. These components are all included within a tiny wafer-level chip-scale package (WLCSP) that can be configured using I2C.
Renesas’s DA9070 PMIC for ultra-low-power battery-powered devices (Source: Renesas Electronics Corp.)
The sequencing feature allows the designer to configure both the order and the time delay for the turn-on/-off of the PMIC’s outputs. This high flexibility allows the power requirements of different components on the mobile device to be met. For example, the display and touch could be switched on after the processor so that the firmware can perform all the required initializations.
Directly related to sequencing is the soft-start feature, which consists of gradual activation, typically following a ramp profile, of the PMIC outputs. This prevents the formation of unwanted inrush currents in the loads, promoting a safe and smooth turn-on of the mobile device.
On a common mobile device, there are typically multiple PMICs, each performing specific functions, such as powering the processor (SoC), camera and display. For certain devices with special electrical requirements, dedicated voltage regulators may be needed. One example is the STMP30 PMIC from STMicroelectronics, designed to provide the positive and negative voltages required by AMOLED displays, which are becoming increasingly popular in the mobile arena.
The STMP30 integrates a triple DC/DC converter that provides the three voltages (two positive and one negative) required to power AMOLED displays. Especially suited for battery-powered devices, this PMIC is configurable via the S-Wire Interface and has advanced built-in features, such as soft start, input undervoltage lockout, short-circuit protection, thermal shutdown and true shutdown mode with low Iq.
Benefits of PMICs for mobile devices
Powered by Li-ion batteries and implemented using high-density ICs, mobile devices can largely leverage the following design benefits that PMICs offer.
High efficiency
PMICs provide accurate and effective control of power, guaranteeing that electronic devices receive the appropriate voltage levels to achieve optimal performance. This results in enhanced energy efficiency and extended battery life in portable devices.
When selecting a PMIC, designers must consider its power consumption, both in standby and in the operating state. Low Iq is a key factor in driving this choice.
Another PMIC suitable for ultra-low-power applications is NXP Semiconductors’ PCA9460, a 13-channel PMIC. The device (Figure 2) offers four high-efficiency 1-A step-down regulators, four LDOs, one SNVS LDO and four 150-mΩ load switches (LED drivers) in a WLCSP42 package. The system has two buck regulators that enable dynamic voltage scaling and offer customizable ramping up and down times.
The PCA9460 is specifically developed to be used in conjunction with the i.MX 8ULP processor, allowing for the implementation of low-power applications. It offers power supply solutions for low-power wearable applications in which size and efficiency are crucial. All LDOs possess a low Iq of 300 nA. Additionally, one LDO is specifically designed to supply power to the SNVS core.
Figure 2: NXP’s PCA9460 PMIC (Source: NXP Semiconductors)
High integration
Combining multiple functions in a single chip, such as voltage regulation, power sequencing and protection circuits, PMICs reduce the need for external components, simplifying the overall design.
Small footprint
The small form factor of PMICs fits well with the reduced physical space available on mobile devices, allowing designers to add more functionality or reduce the PCB size.
Flexibility
Most PMICs include programmable features, such as voltage steps, allowing designers to adjust the power management solution to the specific requirements of the device. A single PMIC can serve multiple designs, requiring only the modification of the configuration parameters.
Protection circuits
PMICs usually offer protection features against under-/overvoltage, overcurrent and overtemperature, mitigating the risk of potential damage to the device and its components.
Sequencing
By managing the power-up and power-down of various components in a timed and ordered way, PMICs prevent potential risks like inrush current, improving the system’s reliability.
Analog Devices Inc.’s MAX20356 is a compact and flexible power management solution designed for extremely energy-efficient wearable devices. The power-optimized voltage regulators consist of several buck converters, a buck-boost converter and linear regulators. These regulators offer a high level of integration and enable the creation of a completely optimized power architecture. The Iq of each regulator is extremely low to prolong the battery life in applications that are always active.
A 1.5-W buck-boost converter with low-noise characteristics is used to achieve efficient power conversion, specifically tailored for the LEDs in optical heart-rate systems like PPG and SpO2 monitoring. The MAX20356 is also furnished with a nano-Iq quick-transient LDO, specifically designed for use in analog front-end sensors.
Battery management
PMICs oversee the battery charging and discharging process, extending the battery life and its safe operation. Additionally, they monitor the battery status and provide information on power consumption in real time.
Although using PMICs offers significant advantages for design, it is important to note that compared with a discrete solution, they require careful configuration and programming of the device and may not always fully adapt to the power requirements of the specific application.
Advertisement
