RHYTHM SB3229
www.onsemi.com
12
transition time. The duration of an Acoustic Indicator is
configurable, with a maximum value of 6.35 seconds.
Power Management
SB3229 has three user−selectable power management
schemes to ensure the hearing aid dies gracefully at the end
of battery life. Shallow reset, Deep reset and Advanced
Reset mode. It also contains a programmable power on reset
delay function.
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.
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 SB3229 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 the average supply voltage is above 0.95 V, an
instantaneous supply voltage fluctuation below 0.95 V will
trigger an immediate 3 dB gain reduction. After the 3 dB
gain reduction has been applied, the advanced reset model
holds off checking the instantaneous voltage level for
a monitoring period of 30 second in order to allow the
voltage level to stabilize. If after the stabilization time the
instantaneous voltage drops a second time below 0.95 V
during the next monitoring period, the gain will be reduced
an additional 3 dB for a 6 dB total reduction and a 30 second
stabilization time is activated. The advanced reset mode
continues to monitor the instantaneous voltage levels over
30 second monitoring periods. If the instantaneous voltage
remains above 1.1 V during that monitoring period, the gain
will be restored to the original setting regardless of whether
one or two gain reductions are applied. If two gain
reductions are applied and the instantaneous voltage level
remains above 1.0 V for a monitoring period, the gain will
be restored to a 3 dB reduction.
Should the average supply voltage drop below 0.95 V, the
device will then reduce the gain by 1 dB every 10 seconds
until either the average supply voltage rises above 0.95 V or
a total of 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 of 0.6 V, 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.
SDA and I
2
C Communication
SB3229 can be programmed using the SDA or I
2
C
protocol. During parameter changes, the main audio signal
path of the hybrid is temporarily muted using the memory
switch fader to avoid the generation of disturbing audio
