How to Integrate Multiple PMICs for Complex SoCs

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What are the Challenges of Providing Power Supplies to complex SoCs?

Application-Specific Integrated Circuits (ASICs) are systems designed and optimized for targeted applications such as industrial, automotive, IoT, mobile, medical, and home automation. A complex ASIC may include different components such as microprocessors, interfaces, and peripheral functions, culminating in a System-on-a-Chip (SoC). The intricate design of SoCs requires extra power supply rails feeding different currents and voltages. These should be powered up and powered down individually under careful control.

Complex PMICs contain several digital and analog functional blocks. The analog circuits regulate sense and monitor with a controller to govern the power-up sequencing and PMIC operation. The controller circuitry may accommodate programmable sequencing logic, microcontrollers, or state machines. Standard power management includes the use of DC-DC converters, low dropout (LDO) linear voltage regulators, safety functions, and voltage monitoring features.

For example, smartphones - the dominant segment of portable consumer devices - come packed with attributes reinforced by sturdy application processors and a lightweight battery that powers GPS, multiple sensors, Bluetooth, NFC, cameras, radios, Wi-Fi, and cellular wireless. These handsets combine multiple PMICs that dynamically administer use and battery life. Figure 1 below shows the Multiple PMICs concept introduced by NXP for optimizing different blocks like computing, safety, and peripherals of a Multi-Processor System.

Figure 1: Multiple PMIC concept for complex SoCs (Image Source: NXP Semiconductors)

PCB Design with PMICs

Power density, signal cross-coupling, component placement, and PCB layer count are crucial areas that designers must consider.  PCB design becomes difficult with the complex integration of multiple power sources within a single PMIC package.

The PCB stack up (the number of PCB layers) must be chalked out before floor planning the said PCB layout with the distinct, dedicated ground, signal, and power layers. A good layer accretion is crucial for differential-mode emissions, external noise susceptibility, common-mode emissions, crosstalk, and electrical performance.

Component placement is essential to any good PCB layout. Components can be placed in different ways based on a specific application. Each PCB must be adjusted appropriately and may come with multiple tradeoffs. It is vital to start with the PMIC input pins during component placement, as input capacitors serve as a local power supply, specifically for transient power demand.

PMIC performance is critical for data integrity and should be secured from hazards like interference and corruption. The layout must direct aggressors away from noise-sensitive signals and safeguard sensitive signals from other onboard aggressors.

Planes and signals constitute another standard PMIC routing layout consideration. It is recommended that the second layer (underneath the component mounting layer) is used as a ground plane, since an IC must have a low-impedance ground. Ground impedance is effectively reduced by components like the input capacitor producing a low parasitic via the connection. The ground plane also functions as a shield against inductive and capacitive noise sources on that component mounting layer.

Buck converters must be of primary consideration when routing the PCB for PMICs, as they comprise switching power sources with integrated powertrains inside the IC. The converter's ground pins and input usually convey considerable amounts of the high-frequency switching current. Inductance and resistance are minimized by routing them using a thick trace. Reduced resistance translates into minimal unwanted power loss, and low inductance keeps the spike in the switching voltage spike to a minimum, to ensure dependable operation.

Trace inductance as minimal as one nH may cause problems. Thicker traces allow efficient, reliable operation and an improved line transient response for both the system and the converter. If the input capacitor and pin are kept in proximity, routing distance will be kept to a minimum, making it easier to accomplish low-impedance routing. Another advantage of such an arrangement is to reduce the chance of inductive coupling, as the input pin connection carries switching current with a superfast edge rate.

Multiple PMICs Concept for High Processing Applications

NXP has introduced the Multiple PMICs Concept for high processing applications that include integrated one-time programmable memory. These store key startup configurations, substantially reducing external components typically used to set output voltage and external regulators' sequence. Regulator parameters can be adjusted via high-speed I2C after startup, offering flexibility for different system states. The following are a few examples of these offerings.

NXP PF71

The PF71 is a power management integrated circuit (PMIC) designed for high performance i.MX 8 processors. It features five high-efficiency buck converters and two linear regulators for powering the processor, memory, and miscellaneous peripherals. It also features a monitoring circuit for safety measures, one-time programmable device configuration, and a 3.4 MHz I2C communication interface. It comes with a 48-pin 7×7 mm QFN package. The KITPF7100FRDMEVM is an evaluation board featuring the PF71 power management IC. The kit integrates all hardware needed to evaluate the featured power management integrated circuit fully.

Figure 2: KITPF7100FRDMEVMKITPF7100FRDMEVM is a customer evaluation board featuring the PF71 power management IC

NXP PF82

The PF81/PF82 is a power management integrated circuit (PMIC) designed for high performance i.MX 8 and S32x based applications. It features seven high-efficiency buck converters and four linear regulators, RTC supply and coin cell charger, watchdog timer/monitor, monitoring circuit to fit ASIL B safety level (PF82), and 3.4 MHz I2C communication interface. It comes with a 56-pin 8 x 8 QFN package. The KITPF8200FRDMEVM is an evaluation board featuring the PF8200 power management IC. It integrates all hardware needed to evaluate the featured power management integrated circuit fully. It combines a communication bridge based on the FRDM-KL25ZFRDM-KL25Z freedom board to interface with the FlexGUI software interface to configure and control the PF8200 PMIC fully.

Figure 3: The KITPF8200FRDMEVMKITPF8200FRDMEVM is an evaluation board featuring the PF82 power management IC

NXP PF5020

The PF5020 is NXP's multi-channel PMIC device designed to be used for high-performance automotive and industrial applications. The PF5020 is also highly configurable, making it a good fit for various system-level power requirements. Integrated and independent voltage monitoring circuits ensure compliance with the ISO 26262 standard and functional safety up to ASIL-B level. The PF5020 is also available as a general non-safety device for applications that don't require ISO compliance. The PF5020 is suitable for multiple applications, including infotainment, ADAS, vision, and RADAR. It can be used either as a standalone power solution or as a companion to another NXP PMIC PF82 or an SBC like the FS85. The KITPF5020FRDMEVM is an evaluation board featuring the PF5020 power management IC. The kit integrates all hardware needed to evaluate the featured power management integrated circuit fully. It integrates a communication interface based on the FRDM-KL25ZFRDM-KL25Z freedom board to fully interface with the FlexGUI software to configure and control the PF5020 PMIC fully.

Figure 4: The KITPF5020FRDMEVMKITPF5020FRDMEVM is an evaluation board for the PF5020 multi-channel (5) PMIC

Power management plays a major role in virtually every piece of electronic equipment. If you'd like to know more about how to approach power management in your designs or products, click here for more information.