THE DESIGN CYCLE
■ BY FRED EADY
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
GIVE YOUR DATA RADIO
Behind every good data
radio, you will find a
microcontroller filled with
tricky radio driver
firmware. In most cases,
the microcontroller that
supports the data radio
moonlights as the LCD
controller, the RS-232
driver, and the analog
interface. These days, you
can pick and choose from
a variety of general-purpose and niche
microcontrollers. There are
specialize in motor control
and those that excel in
number crunching. In this
installment of Design
Cycle, we are going to
closely examine a
microcontroller that was
designed to drive RF ICs.
As its name implies, the
AX8052F100 is based on the tried
and true 8052 microcontroller core.
It comes wrapped in a tiny 28-pin
QFN package. The typical data radio
does not have the luxury of
consuming power on a regular basis.
So, to be able to eat when the radio
eats, the microcontroller in charge of
the radio station must have as low or
lower power consumption figures
than the radio itself.
The AX8052F100 low power
modes include standby, sleep, and
deep sleep. The AX8052F100 sleeps
at 850 nA, 1.5 µA, or 2. 2 µA,
depending on how much of its RAM
you wish to protect while its eyes are
closed. The RAM retention sleep
numbers coincide with 256 bytes,
4 KB, and 8 KB of system RAM.
When the AX8052F100 is actively
computing, the current draw is based
on the microcontroller clock speed.
Typically, it burns 150 µA per MHz.
The AX8052F100’s system clock
can be generated externally or
internally. You can hang a 32.768
kHz tuning fork crystal on the low
power crystal oscillator pins or a 20
MHz crystal on the AX8052F100’s
XTAL pins. A 20 MHz clock can also
originate from the AX8052F100’s
internal 20 MHz RC oscillator.
If your data radio application
needs to be cheap and stingy, you
can call upon the AX8052F100’s
10 kHz/640 Hz super low power
internal RC oscillator. To a data radio,
timing is everything. So, the
AX8052F100 allows you to calibrate
the on-chip RC oscillators using a
reference clock signal.
■ PHOTO 1.Don't fear the AX8052F100's
QFN package! We've experienced laying
them down on copper-clad fiberglass
before (Design Cycle March 2009 issue).