PMIC - Gate Drivers: A Purpose-Built Integrated Circuit

A PMIC (Power Management IC), also known as a power management IC, is a purpose-built integrated circuit whose function is to manage power for the main system, for example.

PMICs are commonly used in devices that use batteries as a power source, such as mobile phones or portable media players. As these devices generally have more than one power source (e.g. batteries and USB power supplies), the system requires multiple power sources of different voltages and the need to control the charging and discharging of the batteries, meeting such requirements in the traditional way would take up a lot of space and increase product development time, hence the emergence of PMICs.

A power management integrated circuit (PMIC) is a highly integrated device with many on-board functional circuit modules. PMICs from ADI with integrated battery chargers or USB power managers solve the battery charging problem by providing multiple system rails in a portable product, all in a small form factor. control supports seamless conversion and manages the power flow between different input sources, such as wall adapters, USB ports and Li-ion batteries, while prioritising power supply to the system load. The efficient switch-mode power supply battery management module supports higher charging currents from wall adapters and USB power supplies. For this series of PMICs, the main features of the battery charger include independent operation, high charging current and overhang voltage accuracy and thermal regulation; in addition, the DC-DC converter includes switching and linear regulators.

PCB Design With PMICs

Power density, signal cross-coupling, component placement and the number of PCB layers are key areas that designers must consider. The complex integration of multiple power supplies in a single PMIC package can make PCB design difficult.

PCB stacking (number of PCB layers) must be considered before laying out said PCB layout with different dedicated ground, signal and power supply layers. Good layer build-up is essential for differential mode emissions, external noise sensitivity, common mode emissions, crosstalk and electrical performance.

The placement of components is essential for any good PCB layout. Components can be placed in different ways depending on the particular application. Each PCB must be adjusted appropriately and may require several trade-offs. During component placement, it is critical to start with the PMIC input pins as the input capacitors are used for local power supply, especially for transient power requirements.

PMIC performance is critical to data integrity and should be secured from hazards such as interference and corruption. The layout must keep attackers away from noise-sensitive signals and protect sensitive signals from other attackers.

Planes and signals form another standard PMIC routing layout consideration. It is recommended that the second layer (below the component mounting layer) be used as a grounding layer, as the IC must have a low impedance to ground. The ground impedance can be effectively reduced by components such as input capacitors, thus creating a low parasitic effect through the connection. The ground layer can also act as a shield for inductive and capacitive noise sources on this component mounting layer.

When routing the PCB for the PMIC, the buck converter must be considered first, as the buck converter includes the switching power supply, which has a power assembly integrated within the IC. The converter's ground pin and input typically transmit a large amount of high-frequency switching current. Inductance and resistance are minimised by using thick wire routing. The reduced resistance minimises unnecessary power losses and the low inductance minimises switching voltage spikes, thus ensuring reliable operation. An alignment inductance of 1 nH minimum can cause problems. Thicker alignments provide efficient, reliable operation of systems and converters and improve line transient response. If the input capacitors and pins are kept close together, the wiring distance will be kept to a minimum, making it easier to achieve low-impedance wiring. Another advantage of this arrangement is that the chance of inductive coupling is reduced, as the input pin connections transmit switching currents at ultra-fast edge rates.

Other Functions of the PMIC

Due to the need to coordinate with the host system, a signal interface is required to communicate with the host system, typically using a serial interface such as I²C or SPI. Some PMICs with simpler functions are connected directly to the MCU's GPIO with a separate signal.

Some PMICs can be connected to a back-up power supply for the real time clock and some have simple power status indicators, such as LEDs to indicate battery charge and discharge status.

Some PMICs are designed for a particular family of MCUs, and the company developing the corresponding MCU will have off-the-shelf firmware to support the operation of the PMIC.

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