ic-wt iC-Haus, ic-wt Datasheet - Page 7

• Manufacturer Part Number: ic-wt
• Description: Incremental Encoder
• Manufacturer: iC-Haus

The line driver iC-WE possesses short-circuit-proof push-pull output stages for the tracks A, B and Z. The
drivers typically supply 300mA at VB= 24V and are internally adapted for a characteristic impedance of 75 .
The outputs can be inverted via input INV (active-high). Consequently, when two line drivers are used, a
balanced activation of the line is also possible. Tri-state switching of the output stages is possible to support bus
systems (input TRI). An error detector monitors the chip temperature as well as the supply voltages VCC and
VB. In the event of a fault, the open-collector output NER is switched low and the output stages are switched
to high impedance to prevent destruction. The error signal of the incremental encoder iC-WT can be switched
through to the output NER via the error input TNER.
DIMENSIONING
Adjusting the LED current control
Since the photodiodes DPA to DNA and DPB to DNB have anti-phase illumination, the following applies for the
control parameter I
Multiplied by the current transmission factor of the LED current control CR(ILR), the current to be set at ILR is
(see electrical characteristics, No.607):
This current can be set with a resistor R
applied to pin ILR, this produces:
Example: As a setpoint, the photodiodes should be illuminated so brightly that it conducts a photocurrent I
400nA at a maximum. With the electrical characteristics No.604 for V(ILR) and No.607 for CR(ILR) the result
is:
Adjusting the index track comparator threshold
The comparator threshold for the index signal is defined via a further reference current. The photocurrent I
is also obtained as the maximum for the photodiode DZ in the event of homogeneous illumination and same
photodiodes for track A/B and track Z. The maximum signal-to-noise ratio is attained with the constant-light
evaluation threshold:
Analogue to the calculation of R
Example: As a setpoint, the threshold I
and No.608 for CR(IZ) the result is:
iC-WT
INCREMENTAL ENCODER
I
I
I
R
I
R
R
R
SUM
ILR
IZ
th
LR
Z
LR
Z
I
I
th
I
ph , max
200 nA 400
V ( IZ )
SUM
I ( IZ )
I ( DPA ) I ( DNA ) I ( DPB ) I ( DNB )
2 400 nA 100
V ( ILR )
2
I ( ILR )
1.22 V
CR ( IZ )
CR ( ILR ) 2 I
1.22
I
th
SUM
2 I
V ( IZ )
CR ( IZ )
as a function of the photocurrent peak value I
ph ,max
15.25 k
V ( ILR )
15.25 k
ph ,max
CR ( ILR )
LR
, it follows that:
CR ( ILR )
th
should be 200nA. With the electrical characteristics No.604 for V(IZ)
LR
connected to AGND. Due to the reference voltage V(ILR) being
2 I
ph , max
ph,max.
of a photodiode:
Rev A0, Page 7/13
ph,max
ph,max
=