IC-NX Datasheet, PDF (8/10 Pages) IC-Haus GmbH – 8-CHANNEL LIGHT-GRID PULSE DRIVER

iC-NX
8-CHANNEL LIGHT-GRID PULSE DRIVER
APPLICATION HINTS
Rev C1, Page 8/10
Light curtains
The circuit in Figure 5 shows several iC-NXs con-
nected as a light curtain, where consecutive LEDs emit
clock-driven light pulses. In this example iCa drives
eight LEDs, with the hardware of the following de-
vice (iCb) specifically programmed to drive just four.
A unique high signal at DINa is shifted from right to left
with the shared pulse at CLK.
When discussing the function of iC-NX it is assumed
that all of the flip-flops in iCa to iCx have been reset,
such as is the case, for example, after the supply volt-
age has been switched on. When the signal at DINa is
high iCa’s current sink is activated and first switched to
LED1 with the rising CLK edge. When DINa is low the
next rising CLK edge resets the first flip-flop FF1 (see
the block diagram on page 1) in iCa, turns off LED1
and deactivates the current sink in iCa. At the same
time FF1 sends the stored information to FF2. FF3
accepts this information via the trailing CLK edge (pro-
vided that SHEN is high) and reactivates the current
sink in the next channel in iCa via DO1.
The pulse diagram in Figure 6 is also valid for the sub-
sequent channels and/or components in the chain, i.e.
the iCs configured as a light curtain make up a clock-
driven shift register which passes on the input infor-
mation. With the ninth clock pulse the second device
shown in the chain (iCb) is activated for four pulses as
programmed.
The layout of the PCB must ensure that the wire resis-
tance of the supply lines and the voltage drop which
occur during operation along the entire length of the
light curtain are sufficiently small. High, short-term
pulse currents are provided by back-up capacitors Ca
to Cx; these should have a low inductance due to the
high increase rate of the current. With suitable capac-
itors the voltage drop caused by a light pulse can be
less than 1 V, i.e. Ca to Cx is 1 µF for a light pulse of
1 A x 1 µs, for example. In practice the actual voltage
drop at the iC is considerably less during a pulse as
charge from the back-up capacitors of neighboring iCs
also flows into the active device.
Low-inductance capacitance can be achieved more
economically by placing several capacitors of low ca-
pacitance in parallel as opposed to using special low-
inductance devices. Leads to the LED anodes and to
iC-NX’s ground pin should be as short as possible.
VDD
LED12 LED11
LED10 LED9
Cb
iCb
RSET ISETb
ISET
LED5
GND
LED4
LED6
LED3
LED7
LED2
LED8
LED1
DOUTb
PROG
VDD
DOUT
Logic
DIN
CLK
SHEN
DINb
LED8 LED7 LED6 LED5
iCa
RSET ISETa
ISET
LED5
GND
LED4
LED6
LED3
LED7
LED2
LED8
LED1
DOUTa
PROG
VDD
DOUT Logic
DIN
CLK
SHEN
LED4 LED3 LED2 LED1
Ca
DINa
GND
4 Channels
8 Channels
CLK
SHEN
Figure 5: Schematic of a chain configuration