IC-OG Datasheet, PDF (7/9 Pages) IC-Haus GmbH – 8-BIT DIFFERENTIAL SCANNING OPTO ENCODER

iC-OG
8-BIT DIFFERENTIAL SCANNING OPTO ENCODER
Rev C1, Page 7/9
ELECTRICAL CHARACTERISTICS
Operating Conditions: VCC= 5V ±10%, Tj= -40..125 °C, unless otherwise noted.
Item Symbol Parameter
Conditions
Control Monitor NER
801 Vs()
Saturation Voltage lo
802 Isc()
Short-Circuit Current lo
803 I0()
Collector Off-state Current
I(NER)= 3.2mA
V(NER)= VCC
NER: off, V(NER)= 0..6V
Tj Fig.
EC
Min.
Typ.
Unit
Max.
0.27
0.4
V
15
27
mA
10
µA
DESCRIPTION OF FUNCTIONS
LED current control
The integrated LED current control with a driver stage controls the LED in accordance with the sum of the
photocurrents from the tracks 0 and 1. Compensation is made for age and dirt, as well as for the reduced
efficiency of the LED caused by rises in temperature.
Fig. 1: LED Current Control and Monitoring
The photodiodes DPO, DNO, DP1 and DN1 act as reference diodes. The sum is output via a current sink to
the comparison point pin CSR. Simultaneously, the resistor R1 at pin ISET (the voltage at the ISET pin is kept
at a constant of approximately 1.22V) supplies a reference current for the current source from VCC, which also
works towards the comparison point pin CSR. The comparison point also receives the amplified current from
the compensation diode DDC in order to compensate for dark currents and for the amplifier input currents.
If there is an optical feedback from the LED to the reference photodiodes, the voltage at the CSR pin adjusts
to satisfy the needs of the power driver for the required transmit current at pin LED. In this instance, the
voltage ratio between I(ISET) and the sum of the photodiode current ISUM is constant (Electrical
Characteristics Nos. 706 and 707). The current flowing through the resistor R1 is the setpoint for the control
and directly presets the desired level of illumination.
An internal capacitor ensures that the control is stable. The comparison point pin CSR is lead out in the
BLCC20 package, enabling an external capacitor C2 to be connected to adapt the control behaviour. Lower
values for R1 require larger values for C2, which also improve the power-supply rejection ratio for the control.
Values from 10nF upwards are recommended.