User's Manual

16
Introducing 5000/5100:
Features
1.3.9 Digital Inputs
There are totally 4 groups of digital inputs. Each is electrically isolated from the
outside world by a photo-coupler. Current must flow through the internal LED to turn
on the output transistor.
A typical 1 mA turn-on current is recommended.
A sample circuit is depicted below.
1 43
2
R
DIN+
DIN-
Vext
external ground
external power
Figure 8: D/I sample circuit
How to decide the R value?
Premise: the LED forward voltage is about 1.15 V.
The recommended R is
Kohms when Vext = 5.0 V, and 10 Kohms when Vext = +12 V.
Table 6: Decide resistance value