5–1
FEATURES
• Couples AC and DC signals
• 0.01% Servo Linearity
• Wide Bandwidth, >200 KHz
• High Gain Stability,
±
0.005%/C
• Low Input-Output Capacitance
• Low Power Consumption, < 15mw
• Isolation T est V oltage, 5300 V AC
RMS
,
1 sec.
• Internal Insulation Distance, >0.4
mm
for VDE
• Underwriters Lab File #E52744
• VDE Approval #0884 (Optional with
Option 1, Add -X001 Suffix)
• IL300G Replaced by IL300-X006
APPLICATIONS
• Power Supply Feedback Voltage/
Current
• Medical Sensor Isolation
• Audio Signal Interfacing
• Isolate Process Control Transducers
• Digital Telephone Isolation
DESCRIPTION
The IL300 Linear Optocoupler consists of
an AlGaAs IRLED irradiating an isolated
feedback and an output PIN photodiode
in a bifurcated arrangement. The feed-
back photodiode captures a percentage
of the LED's flux and generates a control
signal (IP
1
) that can be used to servo the
LED drive current. This technique com-
pensates for the LED's non-linear, time,
and temperature characteristics. The out-
put PIN photodiode produces an output
signal (IP
2
) that is linearly related to the
servo optical flux created by the LED.
The time and temperature stability of the
input-output coupler gain (K3) is insured
by using matched PIN photodiodes that
accurately track the output flux of the
LED.
A typical application circuit (Figure 1)
uses an operational amplifier at the circuit
input to drive the LED. The feedback
photodiode sources current to R1 con-
nected to the inverting input of U1. The
photocurrent, IP1, will be of a magnitude
to satisfy the relationship of (IP1=V
IN
/R1).
DESCRIPTION
(continued)
The magnitude of this current is directly proportional to the feedback transfer gain
(K1) times the LED drive current (V
IN
/R1=K1 • I
F
). The op-amp will supply LED cur-
rent to force sufficient photocurrent to keep the node voltage (Vb) equal to Va
The output photodiode is connected to a non-inverting voltage follower amplifier. The
photodiode load resistor, R2, performs the current to voltage conversion. The output
amplifier voltage is the product of the output forward gain (K2) times the LED current
and photodiode load, R2 (V
O
=I
F
• K2 • R2).
Therefore, the overall transfer gain (V
O
/V
IN
) becomes the ratio of the product of the
output forward gain (K2) times the photodiode load r esistor (R2) to the pr oduct of the
feedback transfer gain (K1) times the input resistor (R1). This reduces to V
O
/V
IN
=
(K2 • R2)/(K1 • R1). The overall transfer gain is completely independent of the LED
forward current. The IL300 transfer gain (K3) is expressed as the ratio of the ouput
gain (K2) to the feedback gain (K1). This shows that the circuit gain becomes the
product of the IL300 transfer gain times the ratio of the output to input resistors [V
O
/
V
IN
=K3 (R2/R1)].
Figure 1. Typical application circuit
Dimensions in inches (mm)
1
2
3
4
8
7
6
5
K2K1
Pin One I.D.
.
268 (6.81)
.
255 (6.48)
34
65
.390 (9.91)
.379 (9.63)
.045 (1.14)
.030 (.76)
4° Typ.
.100 (2.54) Typ.
10° Typ.
3°–9°
.305 Typ.
(7.75) Typ.
.022 (.56)
.018 (.46) .012 (.30)
.008 (.20)
.135 (3.43
)
.115 (2.92
)
12
87
.150 (3.81)
.130 (3.30)
.040 (1.02)
.030 (.76 )
8
7
6
5
K1
VCC
VCC 1
2
3
4
K2
VCC
R1
Vc
R2
IL300
Vb
Va +
-U1
Vin
lp 1
VCC
-U2
+
lp 2
Vo
ut
+
IF
IL300
LINEAR OPTOCOUPLER
5–2
IL300
IL300 Terms
KI—Servo Gain
The ratio of the input photodiode current (I
P1
) to the LED cur-
rent(I
F
). i.e., K1 = I
P1
/ I
F
.
K2—Forward Gain
The ratio of the output photodiode current ( I
P2
) to the LED
current (I
F
), i.e., K2 = I
P2
/ I
F
.
K3—Transfer Gain
The Transfer Gain is the ratio of the Forward Gain to the Servo
gain, i.e., K3 = K2/K1.
∆
K3—Transfer Gain Linearity
The percent deviation of the Transfer Gain, as a function of
LED or temperature from a specific Transfer Gain at a fixed
LED current and temperature.
Photodiode
A silicon diode operating as a current source. The output cur-
rent is pr oportional to the incident optical flux supplied by the
LED emitter. The diode is operated in the photovoltaic or pho-
toconductive mode. In the photovoltaic mode the diode func-
tions as a current source in parallel with a forward biased
silicon diode.
The magnitude of the output current and voltage is depen-
dant upon the load resistor and the incident LED optical flux.
When operated in the photoconductive mode the diode is
connected to a bias supply which reverse biases the silicon
diode. The magnitude of the output current is directly propor-
tional to the LED incident optical flux.
LED (Light Emitting Diode)
An infrared emitter constructed of AlGaAs that emits at 890
nm operates efficiently with drive current from 500
µ
A to 40
mA. Best linearity can be obtained at drive currents between
5 mA to 20 mA. Its output flux typically changes by –0.5%/
°
C
over the above operational current range.
Absolute Maximum Ratings
Symbol Min. Max. Unit
Emitter
Power Dissipation
(T
A
=25
°
C) P
LED
160 mW
Derate Linearly from 25
°
C 2.13 mW/
°
C
Forward Current lf 60 mA
Surge Current
(Pulse width <10
µ
s) lpk 250 mA
Reverse Voltage V
R
5V
Thermal Resistance Rth 470
°
C/W
Junction Temperature T
J
100
°
C
Detector
Power Dissipation P
DET
50 mA
Derate linearly from 25
°
C0.65 mW/
°
C
Reverse Voltage V
R
50 V
Junction Temperature T
J
100
°
C
Thermal Resistance Rth 1500
°
C/W
Coupler
Total Package
Dissipation at 25
°
CP
T
210 mW
Derate linearly from 25
°
C 2.8 mW/
°
C
Storage Temperature T
S
–55 150
°
C
Operating Temperature T
OP
–55 100
°
C
Isolation Test Voltage 5300 VAC
RMS
Isolation Resistance
V
IO
=500 V, T
A
=25
°
C
V
IO
=500 V, T
A
=100
°
C10
12
10
11
Ω
Ω
5–3
IL300
Characteristics
(T
A
=25
°
C)
Symbol Min. Typ. Max. Unit Test Condition
LED Emitter
Forward Voltage V
F
1.25 1.50 V I
F
=10 mA
V
F
Temperature Coefficient
∆
V
F
/
∆°
C -2.2 mV/
°
C
Reverse Current I
R
110
µ
AV
R
=5 V
Junction Capacitance C
J
15 pF V
F
=0 V, f=1 MHz
Dynamic Resistance
∆
V
F
/
∆
I
F
6
Ω
I
F
=10 mA
Switching Time t
R
t
F
1
1
µ
s
µ
s
∆
I
F
=2 mA, I
Fq
=10 mA
∆
I
F
=2 mA, I
Fq
=10 mA
Detector
Dark Current I
D
125nAV
det
=-15 V, I
F
=0
µ
A
Open Circuit Voltage V
D
500 mV I
F
=10 mA
Short Circuit Current I
SC
70
µ
AI
F
=10 mA
Junction Capacitance C
J
12 pF V
F
=0 V, f=1 MHz
Noise Equivalent Power NEP 4 x 10
14
W/
√
Hz V
det
=15 V
Coupled Characteristics
K1, Servo Gain (I
P1
/I
F
) K1 0.0050 0.007 0.011 I
F
=10 mA, V
det
=-15 V
Servo Current, see Note 1, 2 I
P
170
µ
AI
F
=10 mA, V
det
=-15 V
K2, Forward Gain (I
P2
/I
F
) K2 0.0036 0.007 0.011 I
F
=10 mA, V
det=-15 V
Forward Current IP270µAI
F
=10 mA, Vdet=-15 V
K3, Transfer Gain (K2/K1)
See Note 1, 2 K3 0.56 1.00 1.65 K2/K1 IF=10 mA, Vdet=-15 V
Transfer Gain Linearity ∆K3 ±0.25 % IF=1 to 10 mA
Transfer Gain Linearity ∆K3 ±0.5 % IF=1 to 10 mA, TA=0°C to 75°C
Photoconductive Operation
Frequency Response BW (-3 db) 200 KHz IFq=10 mA, MOD=±4 mA, RL=50 Ω,
Phase Response at 200 KHz -45 Deg. Vdet=-15 V
Rise Time tR1.75 µs
Fall Time tF1.75 µs
Package
Input-Output Capacitance CIO 1pFV
F
=0 V, f=1 MHz
Common Mode Capacitance Ccm 0.5 pF VF=0 V, f=1 MHz
Common Mode Rejection Ratio CMRR 130 dB f=60 Hz, RL=2.2 KΩ
Notes
1. Bin Sorting:
K3 (transfer gain) is sorted into bins that are ±5%, as follows:
Bin A=0.557–0.626
Bin B=0.620–0.696
Bin C=0.690–0.773
Bin D=0.765–0.859
Bin E=0.851–0.955
Bin F=0.945–1.061
Bin G=1.051–1.181
Bin H=1.169–1.311
Bin I=1.297–1.456
Bin J=1.442–1.618
K3=K2/K1. K3 is tested at IF=10 mA, Vdet=–15 V.
2. Bin Categories: All IL300s are sorted into a K3 bin, indicated by an
alpha character that is marked on the part. The bins range from “A”
through “J”.
The IL300 is shipped in tubes of 50 each. Each tube contains only
one category of K3. The category of the parts in the tube is marked
on the tube label as well as on each individual part.
3. Category Options: Standard IL300 orders will be shipped from the
categories that are available at the time of the order. Any of the ten
categories may be shipped. For customers requiring a narrower
selection of bins, four different bin option parts are offered.
IL300-DEFG: Order this part number to receive categories D,E,F,G
only.
IL300-EF: Order this part number to receive categories E, F only.
IL300-E: Order this part number to receive category E only.
IL300-F: Order this part number to receive category F only
5–4 IL300
Figure 2. LED forward current vs. forward voltage
Figure 3. LED forward current vs. forward voltage
Figure 4. Servo photocurrent vs. LED current and
temperature
Figure 5. Servo photocurrent vs. LED current
and temperatureFigure
1.41.31.21.11.0
0
5
10
15
20
25
30
35
VF - LED Forward Voltage - V
IF - LED Current - mA
1.0 1.1 1.2 1.3 1.4
.1
1
10
100
VF - LED Forward Voltage - V
IF - LED Current - mA
100101.1
0
50
100
150
200
250
300
0°C
25°C
50°C
75°C
IF - LED Current - mA
IP1- Servo Photocurrent - µA
VD=–15 V
.1 1 10 100
1
10
100
1000
0°C
25°C
50°C
75°C
IF - LED Current - mA
IP1- Servo Photocureent - µA
LED current and temperature
Vd = -15V
VD=–15 V
Figure 6. Normalized servo photocurrent vs. LED
current and temperature
Figure 7. Normalized servo photocurrent vs. LED
current and temperature
Figure 8. Servo gain vs. LED current and temperature
Figure 9. Normalized servo gain vs. LED current
and temperature
2520151050
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0°C
25°C
50°C
75°C
IF - LED Current - mA
Normalized Photocurrent
Normalized to:IP1 @ IF=10 mA,
TA=25°C,
VD=–15 V
100101.1
.01
.1
1
10
0°C
25°C
50°C
75°C
IF - LED Current - mA
IP1- Normalized Photocurrent
Normalized to IP1 @ IF=10 mA,
TA=25°C,
VD=–15 V
100101.1
0.0
0.2
0.4
0.6
0.8
1.0
1.2
IF - LED Current - mA
NK1- Normalized Servo Gain
0°
25°
50°
75°
85°
.1 1 10 100
0.0
0.2
0.4
0.6
0.8
1.0
1.2
IF - LED Current - mA
NK1- Normalized Servo Gain
0°
25°
50°
75°
100°
Normalized to:
IF=10 mA, TA=25°C
5–5 IL300
Figure 10. Transfer gain vs. LED current and temperature
Figure 11. Normalized transfer gain vs. LED current
and temperature
Figure 12. Amplitude response vs. frequency
Figure 13. Amplitude and phase response vs. frequency
2520151050
0.990
0.995
1.000
1.005
1.010
IF - LED Current - mA
K3 - Transfer Gain - (K2/K1)
0°C
25°C
50°C
75°C
0 5 10 15 20 25
0.990
0.995
1.000
1.005
1.010
IF - LED Current - mA
K3 - Transfer Gain - (K2/K1)
0°C
25°C
50°C
75°C
Normalized to IF=10 mA, TA=25°C
10 6
10 5
10 4
-20
-15
-10
-5
0
5
F - Frequency - Hz
Amplitude Response - dB
IF=10 mA, Mod=±2 mA (peak)
RL=10 KΩ
RL=1 KΩ
10 7
10 6
10 5
10 4
10 3
-20
-15
-10
-5
0
5
-180
-135
-90
-45
0
45
dB
PHASE
F - Frequency - Hz
Amplitude Response - dB
Ø - Phase Response -°
IFq=10 mA
Mod=±4 mA
TA=25°C
RL=50 Ω
Figure 14. Common mode rejection
Figure 15. Photodiode junction capacitance vs. reverse
voltage
Application Considerations
In applications such as monitoring the output voltage from a
line powered switch mode power supply, measuring bioelectric
signals, interfacing to industrial transducers, or making floating
current measurements, a galvanically isolated, DC coupled
interface is often essential. The IL300 can be used to construct
an amplifier that will meet these needs.
The IL300 eliminates the problems of gain nonlinearity and drift
induced by time and temperature, by monitoring LED output
flux.
A PIN photodiode on the input side is optically coupled to the
LED and produces a current directly proportional to flux falling
on it . This photocurrent, when coupled to an amplifier, provides
the servo signal that controls the LED drive current.
The LED flux is also coupled to an output PIN photodiode. The
output photodiode current can be directly or amplified to sat-
isfy the needs of succeeding circuits.
Isolated Feedback Amplifier
The IL300 was designed to be the central element of DC cou-
pled isolation amplifiers. Designing the IL300 into an amplifier
that provides a feedback control signal for a line powered
switch mode power is quite simple, as the following example
will illustrate.
See Figure 17 for the basic structur e of the switch mode supply
using the Siemens TDA4918 Push-Pull Switched Power Supply
Control Chip. Line isolation and insulation is provided by the
high frequency transformer. The voltage monitor isolation will
be provided by the IL300.
10 100 1000 10000 100000 1000000
-130
-120
-110
-100
-90
-80
-70
-60
F - Frequency - Hz
CMRR - Rejection Ratio - dB
0
2
4
6
8
10
12
14
0246810
Voltage - Vdet
Capacitance - pF
5–6 IL300
Figure 16. Isolated control amplifier
For best input offset compensation at U1, R2 will equal R3. The
value of R1 can easily be calculated from the following.
The value of R5 depends upon the IL300 Transfer Gain (K3). K3
is targeted to be a unit gain device, however to minimize the
part to part Transfer Gain variation, Siemens offers K3 graded
into % bins. R5 can determined using the following equa-
tion,
Or if a unity gain amplifer is being designed (V
MONI-
TOR
=V
OUT
, R1=0), the euation simplifies to:
+
-
Voltag
e
Monito
r
R1
R2
T
o Control
Input ISO
AMP
+1
R1 R2 VMONITOR
Va
--------------------------- 1–
=
20KΩ30KΩ5V
3V
-------1–
=
5±
R5 VOUT
VMONITOR
--------------------------- R3 R1 R2+()
R2K3
-------------------------------------
•=
R5
R3
K3
-------=
The isolated amplifier provides the PWM control signal which
is derived from the output supply voltage. Figure 16 more
closely shows the basic function of the amplifier.
The control amplifier consists of a voltage divider and a non-
inverting unity gain stage. The TDA4918 data sheet indicates
that an input to the control amplifier is a high quality operational
amplifier that typically requires a +3V signal. Given this infor-
mation, the amplifier circuit topology shown in Figure 18 is
selected.
The power supply voltage is scaled by R1 and R2 so that
there is +3 V at the non-inverting input (Va) of U1. This voltage
is offset by the voltage developed by photocurrent flowing
through R3. This photocurrent is developed by the optical flux
created by current flowing through the LED. Thus as the
scaled monitor voltage (Va) varies it will cause a change in the
LED current necessary to satisfy the differential voltage
needed across R3 at the inverting input.
The first step in the design procedure is to select the value of
R3 given the LED quiescent current (IFq) and the servo gain
(K1). For this design, IFq=12 mA. Figure 4 shows the servo pho-
tocurrent at IFq is found to be 100 µA. With this data R3 can be
calculated. R3
V
b
IPl
------ 3V
100µA
------------------
== 30KΩ=
Figure 17. Switch mode power supply
Figure 18. DC coupled power supply feedback amplifier
SWITCH
XFORMER
SWITCH
MODE
R
EGULATO
R
TDA4918
ISOLATED
F
EEDBAC
K
CONTROL
110/
2
20
M
AI
N
DC OUTPUT
AC/DC
R
ECTIFIE
R
AC/DC
R
ECTIFIE
R
8
7
6
5
100 pF
4
3
1
28
6
7
K1
VCC
VCC 1
2
3
4
K2
VCC
V
monitor
R1
20 KΩ
R2
30 KΩ
R3
30 KΩ
R4
100 Ω
Vout To
contro
l
input
R5
30 KΩ
IL300
Vb
Va +
-
U1
LM201
5–7 IL300
Table 1 gives the value of R5 given the production K3 bins.
Table 1. R5 selection
The last step in the design is selecting the LED current limiting
resistor (R4). The output of the operational amplifier is targeted
to be 50% of the Vcc, or 2.5 V. With an LED quiescent current of
12 mA the typical LED (VF ) is 1.3 V. Given this and the opera-
tional output voltage, R4 can be calculated.
.
The circuit was constructed with an LM201 differential opera-
tional amplifier using the resistors selected. The amplifier was
compensated with a 100 pF capacitor connected between pins
1 and 8.
The DC transfer charateristics are shown in Figure 19. The
amplifier was designed to have a gain of 0.6 and was mea-
sured to be 0.6036. Greater accurracy can be achieved by
adding a balancing circuit, and potentiometer in the input
divider, or at R5. The circuit shows exceptionally good gain lin-
earity with an RMS error of only 0.0133% over the input voltage
range of 4 V–6 V in a servo mode; see Figure 20.
Figure 19. Transfer gain
Bins Min. Max. K3
Typ.
R5
Resistor
KΩ
1%
KΩ
A 0.560 0.623 0.59 50.85 51.1
B 0.623 0.693 0.66 45.45 45.3
C 0.693 0.769 0.73 41.1 41.2
D 0.769 0.855 0.81 37.04 37.4
E 0.855 0.950 0.93 32.26 32.4
F 0.950 1.056 1.00 30.00 30.0
G 1.056 1.175 1.11 27.03 27.0
H 1.175 1.304 1.24 24.19 24.0
I 1.304 1.449 1.37 21.90 22.0
J 1.449 1.610 1.53 19.61 19.4
R4 Vopamp VF
–
IFq
-------------------------------- 2.5V 1.3V–
12mA
------------------------------ 100 Ω===
6.05.55.04.54.0
2.25
2.50
2.75
3.00
3.25
3.50
3.75
Vin - Input Voltage - V
Vout - Ooutput Voltage - V
Vout = 14.4 mV + 0.6036 x Vin
LM 201 Ta = 25°C
Figure 20. Linearity error vs. input voltage
The AC characteristics are also quite impressive offering a -3
dB bandwidth of 100 KHz, with a -45° phase shift at 80 KHz as
shown in Figure 21.
Figure 21. Amplitude and phase power supply control
The same procedure can be used to design isolation amplifiers
that accept biploar signals referenced to ground. These amplifi-
ers circuit configurations ar e shown in Figure 22. In or der for the
amplifier to respond to a signal that swings above and below
ground, the LED must be prebiased from a separate source by
using a voltage reference source (Vr ef1). In these designs, R3
can be determined by the following equation.
6.05.55.04.54.0
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
0.020
0.025
Vin - Input Voltage - V
Linearity Error - %
LM201
10310 410510 6
-8
-6
-4
-2
0
2
-180
-135
-90
-45
0
45
dB
PHASE
F - Frequency - Hz
Amplitude Rresponse - dB
Phase Response - °
R3
V
ref1
IP1
-------------
V
ref1
K1IFq
---------------==
5–8 IL300
These amplifiers provide either an inverting or non-inverting
transfer gain based upon the type of input and output amplifier.
Table 2 shows the various configurations along with the spe-
cific transfer gain equations. The offset column refers to the
calculation of the output offset or Vref2 necessary to provide a
zero voltage output for a zero voltage input. The non-inverting
input amplifier requires the use of a bipolar supply, while the
inverting input stage can be implemented with single supply
operational amplifiers that permit operation close to ground.
For best results, place a buf fer transistor between the LED and
output of the operational amplifier when a CMOS opamp is
used or the LED IFq drive is targeted to operate beyond 15 mA.
Finally the bandwidth is influenced by the magnitude of the
closed loop gain of the input and output amplifiers. Best band-
widths result when the amplifier gain is designed for unity.
Figure 22. Non-inverting and inverting amplifiers
Table 2. Optolinear amplifiers
Amp[ifier Input Output Gain Offset
Non-Inverting Inverting Inverting
Non-Inverting Non-Inverting
Inverting Inverting Non-Inverting
Non-Inverting Inverting
Vcc
20pF
4
1
2
3
4
8
7
6
5
+Vref2
R5
R6
7
2
4
3Vo
R4
R3
–Vref1
Vin
R1 R2
37
6
+
+Vcc
100Ω
6
IL300
2–Vcc
–Vcc
Vcc
–Vcc
+
Vcc
Vcc
20pF
4
1
2
3
4
8
7
6
5
+Vref2
7
24
3
Vout
R4
R3
+Vref1
Vin
R1 R2
37
6
+
+Vcc
100Ω
6
2Vcc Vcc
–Vcc
+
Vcc
–
–
Non-Inverting Input Non-Inverting Output
Inverting Input Inverting Output
IL300
–
–
–Vcc
VOUT K3 R4 R2
VIN R3 (R1+R2)
=Vref1 R4 K3
R3
Vref2=
VOUT K3 R4 R2 (R5+R6)
VIN R3 R5 (R1 +R2)
=–Vref1 R4 (R5+R6) K3
R3 R6
V
ref2=
VOUT –K3 R4 R2 (R5+R6)
VIN R3 R5 (R1 +R2)
=Vref1 R4 (R5+R6) K3
R3 R6
Vref2=
VOUT –K3 R4 R2
VIN R3 (R1 +R2)
=–Vref1 R4 K3
R3
Vref2=
