Extend battery life in portable applications using PMIC

1. Introduction

If we consider power management integrated circuits (PMICs) to be solely for powering the system processor, allow me to introduce application-specific PMICs. Application-specific PMICs offer the same significant system advantages as general-purpose PMICs—including reduced system cost, space savings, power sequencing, and platform scalability—but they are typically smaller devices designed for end-device systems. Furthermore, application-specific PMICs feature ultra-low leakage current, contributing to extended battery life in portable applications. In this article, I will describe two example applications of application-specific PMICs.

2. Compact Camera Module (CCM) for Dual-Camera Applications

Current versions of portable electronics, such as smartphones, tablets, and laptops, now use two cameras: a "world-facing" camera and a "user-facing" camera. Integrating these two cameras into end devices such as smartphones, tablets, and detachable laptops requires an integrated, efficient power supply solution. Application-specific PMICs like the TPS68470 can power compact camera modules (CCMs) in dual-camera applications: generating a clock for the image sensor, driving light-emitting diodes (LEDs) for the camera flash and various indicator lights, and providing the driver for integrated LED privacy indicators.

    The PS68470 is an advanced power management unit that powers a small camera module (CCM), generates a clock for the image sensor, drives dual LED flashing, and integrates two LED drivers for general-purpose indicator lights. The TPS68470 is capable of generating all the necessary power rails within the CCM.
The core voltage regulator is a state-of-the-art buck converter for the image sensor's digital power supply, and an LDO (LDO_ANA) is available for the image sensor's analog power supply.
The TPS68470 also features a high-efficiency boost converter to support two 1A LED flash drivers. LED current is controlled by a regulated low-side current source.

Because camera sensor modules are highly sensitive to local electrical noise, system designers must consider methods to reduce this noise. The camera PMIC integrates clean power rails to mitigate this noise. While discrete power supply implementations require additional logic components to be designed on-board, the PMIC integrates power sequencing components, thereby reducing the solution size and the amount of sequencing design work.

Figure 1 shows a high-level block diagram of a PMIC that can power a dual-camera module.

Figure 1: TPS68470 Block Diagram

3. Electronic Paper Display (EPD) Applications

Electronic paper displays (EPDs) can display images even without a power connection. EPDs are also very thin (60µm), giving them an advantage in space-constrained applications. These advantages allow us to add displays to products with challenging power and space limitations.

Electronic ink works by moving positively and negatively charged microcapsules suspended in a transparent solution when an electric charge is applied. EPD applications require multiple output power rails, such as the low input power supply for displays, including ±15V.

Figure 2 is a schematic diagram of the application of TPS65185.

Figure 2: Typical application schematic of TPS65185

Application-specific PMICs like the TPS65185 integrate the necessary power rails into a single device, providing an efficient and space-saving solution for EPD. The TPS65185 handles are sequenced and I²C-controlled to accommodate specific power requirements.

    The TPS65185x is a single-chip power supply designed for E-Ink Vizplex displays used in portable e-reader applications, supporting panel sizes of 9.7 inches and above. Two high-efficiency DC-DC boost converters generate ±16-V rails, which are boosted to 22 V and -20 V via two switching pumps to power the gate drivers for the Vizplex panel. Two tracking LDOs generate ±15-V power drive power, supporting output currents up to 120/200 mA (TPS65185/TPS651851). All rails are adjustable via an I²C interface to suit specific panel requirements.
Precise backplane bias is provided by a linear amplifier, adjustable from 0 V to -5.11 V via a 9-bit control through a serial interface; it can either generate or sink current depending on panel conditions. The TPS65185x supports automatic panel bounce voltage measurement, eliminating the need for manual VCOM calibration on the production line. Measurement results can be stored in non-volatile memory as new VCOM power-on defaults.

These are two examples of application-specific PMICs. A PMIC is more than just a power solution for powering the entire system. Application-specific PMICs help integrate a small number of power rails into a single IC to power dedicated system modules, while still providing the same significant advantages as a general-purpose PMIC.