t
TIL300, TIL300A
PRECISION LINEAR OPTOCOUPLER
t
TAOS018 鈥?AUGUST 1999
D
D
D
D
D
ac or dc Signal Coupling
Wide Bandwidth . . . >200 kHz
High Transfer-Gain Stability . . .
鹵0.005%/擄C
3500 V Peak Isolation
Typical Applications
鈥?Power-Supply Feedback
鈥?Medical-Sensor Isolation
鈥?Opto Direct-Access Arrangement (DAA)
鈥?Isolated Process-Control Transducers
DCS OR P PACKAGE
(TOP VIEW)
LEDK
LEDA
PDK1
PDA1
1
2
3
4
8
7
6
5
NC
NC
PDK2
PDA2
NC 鈥?No internal connection
Description
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 connected to the inverting input of the input
operational amplifier. The photocurrent I
P1
assumes a magnitude that satisfies the relationship I
P1
= V
I
/R1. The
magnitude of the current is directly proportional to the LED current through the feedback transfer gain
K1(V
I
/R1 = K1
脳
I
F
). The operational amplifier supplies LED current to produce sufficient photocurrent to keep
the node voltage V
b
equal to node voltage V
a.
TIL300
1
1V
CC+
V
a
V
b
+
V
I
鈥?/div>
R1
I
P1
+
_
1V
CC鈥?/div>
R3
I
F
1V
CC+
3
P
2
K1
6
2V
CC+
2V
CC+
鈥?/div>
4
5
I
P2
R2
+
2V
CC鈥?/div>
V
O
= K3(R2/R1) V
I
K2
P
NOTES: A. K1 is servo current gain, the ratio of the feedback servo photodiode current (I
P1
) to the input LED current (I
F
), i.e. K1 = I
P1
/I
F.
B. K2 is forward gain, the ratio of the output photodiode current (I
P2
) to the input LED current (I
F
), i.e. K2 = I
P2
/I
F
.
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 V
O
= K2I
F
R2. Overall transfer gain V
O
/V
I
becomes
V
O
/V
I
= (K2I
F
R2/K1I
F
R1). Factoring out the LED forward current I
F
and remembering that K2/K1 = K3, the
overall transfer gain becomes V
O
/V
I
= K3R2/R1. The overall transfer gain, therefore, is shown to be
independent of the LED current.
Copyright
漏
2000, TAOS Inc.
www.taosinc.com
Texas Advanced Optoelectronic Solutions Inc.
800 Jupiter Road, Suite 205
S
Plano, TX 75074
S
(972) 673-0759
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