RHYTHM SB3231
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13
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 Rhythm SB3231 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 of 0.6 V, 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.
SDA and I
2
C Communication
Rhythm SB3231 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 transients. Once the changes are complete, the main
audio path is reactivated. Any changes made during
programming are lost at power−off unless they are explicitly
burned to EEPROM memory.
Improvements have been made to the ARK software,
resulting in improved communication speed. Certain
parameters in ARKonline
®
can be selected to reduce the
number of pages that need to be read out. In SDA mode,
Rhythm SB3231 is programmed via the SDA pin using
industry standard programming boxes. I
2
C mode is
a two−wire interface which uses the SDA pin for
bidirectional data and CLK as the interface clock input. I
2
C
programming support is available on the HiPro (serial or
USB versions) and ON Semiconductor’s DSP
Programmer 3.0.
Input Connection and Layout Considerations
It is recommended to connect unused audio input pins
directly to MGND to minimize the possibility of noise
pickup. Inputs are internally AC coupled, so there is no
additional leakage current when inputs are connected
directly to ground.
In order to further minimize noise at the inputs the following
guidelines are recommended:
• MGND is used as reference ground plane for input
signals. All input components should be grounded to
MGND. This ground plane should be isolated from all
other ground connections in the system.
• Keep the input traces as short as possible and avoid
routing traces near high noise sources such as the
OUT+ and OUT− pins
• Star ground input component grounds to the MGND
connection.
Unused trimmer inputs should also be connected to GND.
