IC-LNB_16 Datasheet, PDF (24/37 Pages) IC-Haus GmbH – 18-BIT OPTO ENCODER

iC-LNB 18-BIT OPTO ENCODER ^preliminary
WITH SPI AND SER/PAR INTERFACES
CS
SCLK
MOSI
MISO
OP ADR DATA1 DATA2 ...
OP
ADR DATA1 DATA2 ...
8 cycles
Figure 14: Write to REGISTER (cont.)
Rev B2, Page 24/37
GRAY-CODE OUTPUTS
In interface mode the outputs GA, GB provide two
90° shifted digital signals with 1 PPR each (Fig-
ure 15). The signals are independent of the Flex-
Count resolution (RESSUB) or the zero position
(ZPOS), but pin DIR or register bit DIR can be
applied to invert the signal GA (code inversion).
Thereby GA and GB can be used for instance to
trigger an external multiturn to count the revolutions.
0°
90°
180°
270°
360°
GA (MSB)
GB (MSB-1)
V10 (DA10V)
N10 (DA10N)
V9 (DA9V)
N9 (DA9N)
One revolution
Figure 15: Phase of GA, GB without code inversion
ADJUSTMENT
iC-LNB is adjusted in relation to the code disc with the
help of an electronic alignment aid.
Tilt angle
In interface mode (EPG = 0) an EXORed signal from
tracks DA4V and DA10V (differential signal of the lead-
ing track 4 and track 10 diodes) is output at pin XJD.
By tilting iC-LNB output signal XJD can be given a mini-
mum spike length at 0° and 180°.
The falling or rising edge of signal GA (MSB bit in inter-
face mode) marks the 0° and 180° positions.
The maximum tilt angle tolerated by the system is stip-
ulated by the resolution and the diameter of the code
disc. Table 15 shows the allocation of the maximum tilt
to the relevant code disc.
Code disc
LNB1S 42-1024
LNB4S 26-1024
tilt angle max.
1.8°
1.0°
Table 15: Maximum tilt angle referenced to the chip’s
center
Example: LNB1S 42-1024
The scan ratio for the adjustment signal at XJD can be
derived from the maximum tilt. At a tilt angle of 1.8°
photodiode DA4V is approximately 74 µm from the ideal
position; with an average radius of 19.89 mm for track
DA4 there is an edge shift of 0.06%. The edge shift for
photodiode DA10V is contradirectional and about the
same size. A spike length of t/T = 0.12% is thus accrued
for a maximum tilt angle of 1.8°. If we were to take half
of the maximum tilt angle as a target alignment, i.e.
0.9°, the device must be aligned to a spike length of
(t/T) < 0.06%.
Spike length t can be computed dependent on the
speed. Under optimum conditions the maximum spike
length is t = 0.0006 / revs per second. Due to imperfect
light levels, code disc tolerances, etc. a spike length
of about half this maximum value should be aimed for
(e.g. of less than 60 µs for a speed of 300 rpm).
The maximum spike length must be adhered to for both
spikes (at 0° and 180°); ideally, both spikes should be
the same length.