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