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

25

20

15

10

5

0

0.990

0.995

1.000

1.005

1.010

IF - LED Current - mA

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

0

°C

25

°C

50

°C

75

°C

10 6

10 5

10 4

-20

-15

-10

-5

0

5

F - Frequency - Hz

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

Mod=

±4 mA

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 structure 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

0

2

4

6

8

10

12

14

02

46

8

10