IC-TW11 Datasheet, PDF (19/25 Pages) IC-Haus GmbH – 10-BIT ULTRA LOW POWER MAGNETIC ABSOLUTE ROTARY ENCODER

iC-TW11 10-BIT ULTRA LOW POWER^preliminary
MAGNETIC ABSOLUTE ROTARY ENCODER
• SAMPLE input samples on falling edge.
• SPI sampling enabled.
• IRQ_OUT = IRQ_IN AND conversion complete.
• Automatic gain control (AGC) enabled.
• Normal power operating mode.
Rev B1, Page 19/25
When using the default configuration, it is not neces-
sary to write to the GAIN register since the iC-TW11’s
AGC is enabled. If the AGC is disabled by setting CON-
FIG.noagc = 1, proper Hall array gain must be set by
writing the appropriate value to the GAIN register.
STARTUP (DEFAULT CONFIGURATION)
At power-up or after the external reset input, xRST, has
been deactivated, the iC-TW11 is in its default state
with all registers at 0x00. Specifically, the default state
is:
• SAMPLE input samples on falling edge.
• SPI sampling enabled.
• IRQ_OUT = IRQ_IN AND conversion complete.
Typically, the default gain used for the first sample and
conversion is too low, resulting in a conversion warning
(warn = 1) due to ADC underflow (STATUS.uflo = 1). In
this case, the AGC increments the GAIN register value
by 1 to increase the gain for the next sample by ap-
proximately 1.5 dB. The next sample uses this new gain
and the AGC again increments (or decrements) the
GAIN register value by 1 depending on the conversion
status after the conversion is complete. This process is
repeated for all subsequent samples.
• Automatic gain control (AGC) enabled.
• Normal power operating mode.
• Lowest Hall array gain.
Thus, after startup it can take up to 18 samples for the
AGC to determine the proper Hall array gain. Therefore,
it is recommended to implement one of the following
techniques in the host at startup:
At startup with the default configuration, the AGC is en-
abled and the Hall array gain is at its lowest value. The
first sample (initiated by a command packet with sup =
0 or a falling edge on the SAMPLE input) uses this
default gain. After the conversion, the AGC determines
whether the Hall signal amplitudes were in the proper
range and sets the conversion warning bit (warn) of the
response packet and the ADC overflow (STATUS.oflo)
and underflow (STATUS.uflo) bits accordingly.
1. Take 20 samples and discard the results.
2. Sample until a response packet with no conver-
sion warning (warn = 0) is returned or until the
STATUS register has a value of 0x00.
3. Write the known gain value for your application
(determined by experimentation) to the GAIN reg-
ister before initiating sampling.
CONVERSION WARNINGS
When reading the ANGLE, SIN, COS, HALL0,
HALL120, or HALL240 Registers, the status of the most
recent conversion is given by the busy (busy) and con-
version warning (warn) bits in the response packet. If
the busy bit is set, the angle information should be dis-
carded and a new sample initiated. Depending on the
application requirements, if the conversion warning bit
is set, the conversion may need to be performed again.
Typically, occasional or random conversion warnings
may be safely ignored; consistent warnings may indi-
cate a misaligned magnet or loss of magnet (airgap too
large).
Conditions that set the conversion warning (warn) bit
are:
1. ADC overflow. The measured Hall signal ampli-
tudes were too high. The AGC lowers the Hall
sensor gain for the next conversion. An ADC
overflow status bit is also available. See STATUS
register on page 16 for more information.
2. ADC underflow. The measured Hall signal am-
plitudes were too low. The AGC raises the Hall
sensor gain for the next conversion. An ADC un-
derflow status bit is also available. See STATUS
register on page 16 for more information.