SA3291 Datasheet, PDF (16/20 Pages) ON Semiconductor – Preconfigured Wireless DSP System for Hearing Aids

AYRE SA3291
Power On Reset Delay
The programmable POR delay controls the amount of
time between power being connected to the hybrid and the
audio output being enabled. This gives the user time to
properly insert the hearing aid before the audio starts,
avoiding the temporary feedback that can occur while the
device is being inserted. During the delay period,
momentary button presses are ignored.
NOTE:
The values set in IDS are relative values from 0
to 11 seconds; not absolute. The POR delay is
relative to the configuration loaded on the
WOLVERINE platform.
Power Management Functionality
As the voltage on the hearing aid battery decreases, an
audible warning is given to the user indicating the battery
life is low. In addition to this audible warning, the hearing
aid takes other steps to ensure proper operation given the
weak supply. The exact hearing aid behaviour in low supply
conditions depends on the selected POR mode. The hearing
aid has three POR modes:
• Shallow Reset Mode
• Deep Reset Mode
• Advanced Mode
Shallow Reset Mode
In Shallow Reset mode, the hearing aid will operate
normally when the battery is above 0.95 V. Once the supply
voltage drops below 0.95 V the audio will be muted and
remain in that state until the supply voltage rises above
1.1 V. Once the supply voltage drops below the control logic
ramp down voltage, the device will undergo a hardware
reset. At this point, the device will remain off until the supply
voltage returns to 1.1 V. When the supply voltage is below
the control logic voltage, but above 0.6 V and rises above the
1.1 V turn on threshold, the device will activate its output
and operate from the memory that was active prior to reset.
If the supply voltage drops below 0.6 V, and rises above the
1.1 V turn on threshold, the device will reinitialize, activate
its output and operate from memory A.
Deep Reset Mode
In Deep Reset mode, the hearing aid will operate normally
when the battery is above 0.95 V. Once the supply voltage
drops below 0.95 V the audio will be muted. The device
remains in this state until the supply voltage drops below the
hardware reset voltage of 0.6 V. When this occurs, the
device will load memory A and operate normally after the
supply voltage goes above 1.1 V.
Advanced Reset Mode
Advanced Reset Mode on Ayre SA3291 is a more
sophisticated power management scheme than shallow and
deep reset modes. This mode attempts to maximize the
device’s usable battery life by reducing the gain to stabilize
the supply based on the instantaneous and average supply
voltage levels. Instantaneous supply fluctuations below
0.95 V can trigger up to two 3 dB, instantaneous gain
reductions. Average supply drops below 0.95 V can trigger
up to eighteen, 1 dB average gain reductions.
While operating with no instantaneous gain reductions, an
instantaneous supply voltage fluctuation below 0.95 V will
trigger an immediate 3 dB gain reduction. A waiting period
of 30 seconds is in place after the first instantaneous gain
reduction. Only after the waiting period has elapsed will an
instantaneous supply voltage fluctuation trigger the second
3 dB gain reduction. While an instantaneous gain reduction
is being applied, the instantaneous supply voltage level will
be checked every 30 seconds and a 3 dB gain reduction
removed should the level be above a certain threshold.
Should the average supply voltage drop below 0.95 V, the
device will begin to reduce the gain by 1 dB every 10
seconds until either the average supply voltage rises above
0.95 V or all 18 average gain reductions have been applied,
at which point the audio path will be muted. If the average
supply voltage returns to a level above 1.1 V, the audio path
will first be un−muted, if required. The gain will then be
increased by 1 dB every 10 seconds until either the average
supply voltage drops below 1.1 V, or all average gain
reductions have been removed. No action is taken while the
average supply voltage resides between 0.95 V and 1.1 V.
NOTE: Instantaneous and average gain reductions are
adjusted independently.
When the instantaneous voltage falls below the hardware
shutdown voltage, the device will undergo a hardware reset.
When it turns back on because the voltage has risen above
the turn−on threshold, it will behave the same as it would in
shallow reset mode.
Low Battery Notification
Notification of the low battery condition via an acoustic
indicator is optionally performed when the battery voltage
drops below a configurable low battery notification
threshold. The low battery indicator is repeated every five
minutes until the device shuts down.
Software and Security
The Ayre SA3291 incorporates the following security
features to protect the device from cloning and against
software piracy:
• DLL protection by password − prevents a third party
from using IDS to reconfigure parts.
• Hybrid authentication by 128−bit fingerprint to identify
parts in application software − prevents a third party
from cloning a device’s EEPROM because the
fingerprint cannot be overwritten. Special functions can
be used in fitting software to reject parts that do not
match the expected fingerprint. This would prevent the
piracy of fitting software.
• DLL to hybrid pairing by using a software key in ARK
to match product libraries with client software − a part
can be ‘locked’ at manufacturing time so that it only
communicates with the library it was programmed with.
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