TIL300 PRECISION LINEAR OPTOCOUPLER
ac or dc Signal Coupling
Wide Bandwidth . . . >200 kHz
High Transfer-Gain Stability . . . ±0.005%/°C
3500 V Peak Isolation
– Power-Supply Feedback
– Medical-Sensor Isolation
– Opto Direct-Access Arrangement (DAA)
– Isolated Process-Control Transducers
The TIL300 precision linear optocoupler consists
of an infrared LED irradiating an isolated feedback photodiode
and an output photodiode in a bifurcated arrangement.
The feedback photodiode captures a percentage of the flux
of the LED that can be used to generate a control signal to regulate the LED drive current.
This technique is used to compensate for the nonlinear time
and temperature characteristics of the LED.
The output-side photodiode then produces an output signal
that is linearly proportional to the servo-optical flux emitted from the LED.
A typical application circuit (shown in Figure 1)
uses an operational amplifier as the input to drive the LED.
The feedback photodiode sources current through R1,
which is onnected to the inverting input of the input operational amplifier.
The photocurrent IP1 assumes a magnitude that satisfies the relationship IP1 = VI/R1.
The magnitude of the current is directly proportional to the LED current
through the feedback transfer gain K1(VI/R1 = K1 × IF).
The operational amplifier supplies LED current to produce sufficient photocurrent
to keep the node voltage Vb equal to node voltage Va.
A. K1 is servo current gain, the ratio of the feedback servo photodiode current (IP1)
to the input LED current (IF), i.e. K1 = IP1/IF.
B. K2 is forward gain, the ratio of the output photodiode current (IP2)
to the input LED current (IF), i.e. K2 = IP2/IF.
C. K3 is transfer gain, the ratio of the forward gain to the servo gain,
i.e. K3 = K2/K1.
Figure 1. Typical Application Circuit
The output photodiode is connected to a noninverting voltage follower;
R2 is used to develop a voltage from the photodiode current.
The output of the amplifier is VO = K2IFR2.
Overall transfer gain VO/VI becomes VO/VI = (K2IFR2/K1IFR1).
Factoring out the LED forward current IF and remembering that K2/K1 = K3,
the overall transfer gain becomes VO/VI = K3R2/R1.
The overall transfer gain, therefore, is shown to be independent of the LED current.
LEDK 1 LED cathode
LEDA 2 LED anode
PDK1 3 Photodiode 1 cathode
PDA1 4 Photodiode 1 anode
PDA2 5 Photodiode 2 anode
PDK2 6 Photodiode 2 cathode
NC 7 No internal connection
NC 8 No internal connection
Stresses beyond those listed under “absolute maximum ratings”
may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these conditions is not implied.
Exposure to absolute-maximum-rated conditions for extended periods may
affect device reliability.
1. Derate linearly from 25°C at a rate of 2.66 mW/°C.
2. Derate linearly from 25°C at a rate of 0.66 mW/°C.
3. Derate linearly from 25°C at a rate of 3.33 mW/°C.
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