Electronic Design

Codec And System Power Management Share A Die

Put the whole power system for a portable audio and navigation system on the same die as the system's audio codec? That's what Wolfson Microelectronics has done in its Audio- Plus codec line. OEMs would like shorter bills of materials and more compact board layouts, but what's going to be integrated? Wolfson says mixed-signal audio and system power make the most sense.

There are now three philosophies for power management in portable devices. We've seen the first two: centralize power management and run separate voltage rails to each chip; or, bus a common voltage around the board and locate separate dc-dc converters where needed, having them operate autonomously or under orders from a central controller via a simple control bus. AudioPlus represents the third option.

The first AudioPlus chip, the WM8350, is a high-fidelity, stereo codec with advanced mixing capability (see the figure). It provides six analog inputs, two stereo analog outputs, and two mono line outputs. Also, it drives headphones directly. It has an onchip clock generator and an auxiliary analog- to-digital converter (ADC) as well. The key performance number, signal- to-noise ratio (SNR), is 98 dB.

The power portion of the chip integrates six dcdc converters, four low-dropout regulators (LDOs), a battery charger, and two white-LED drivers. A built-in power-management controller is responsible for the output voltage settings, startup sequencing, and managing the lowpower modes.

Four of the 2-MHz, more than 90% efficient dc-dc converters are buck-mode regulators to generate the supplies for the system's CPU core, I/O, memory devices, and other system peripherals. Each output voltage is separately programmable between 0.85 and 3.4 V in 25-mV steps.

Two 1-MHz dc-dc converters are boost regulators for backlight displays and USB On-The-Go (USB/OTG). The four 150-mA low-noise LDOs supply the audio codec itself, an external phase-locked loop (PLL), and other system functions. Output voltage can be set between 0.9 and 3.3 V in 50- or 100-mV steps.

The single-cell lithium battery charger supports programmable target voltage, trickle and fast charge modes, and various safety features for the end application. Autonomous power-supply selection from USB and/or an ac adapter enables "instant on" even when the battery is dead.

This all comes in a 7- by 7-mm, 129-pin ball-grid array (BGA) package. Unit-pricing is $4.32 in 10,000-piece quantities.

Wolfson Microelectronics www.wolfsonmicro.com

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