IL300 datasheet(11/15 Pages) VISHAY

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VISHAY

IL300

Document Number 83622

Rev. 1.4, 26-Oct-04

Vishay Semiconductors

www.vishay.com

The last step in the design is selecting the LED cur-

rent limiting resistor (R4). The output of the opera-

tional 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

operational amplifier using the resistors selected. The

amplifier was compensated with a 100 pF capacitor

connected between pins 1 and 8.

The DC transfer characteristics are shown in Figure

19. The amplifier was designed to have a gain of 0.6

and was measured to be 0.6036. Greater accuracy

can be achieved by adding a balancing circuit, and

potentiometer in the input divider, or at R5. The circuit

shows exceptionally good gain linearity with an RMS

error of only 0.0133 % over the input voltage range of

4.0 V - 6.0 V in a servo mode; see Figure 20.

The AC characteristics are also quite impressive

offering a - 3.0 dB bandwidth of 100 kHz, with a -45 °

phase shift at 80 kHz as shown in Figure 21.

The same procedure can be used to design isolation

amplifiers that accept bipolar signals referenced to

ground. These amplifiers circuit configurations are

shown in Figure 22. In order for the amplifier to

respond to a signal that swings above and below

ground, the LED must be pre biased from a separate

source by using a voltage reference source (Vref1). In

these designs, R3 can be determined by the following

equation.

Figure 19. Transfer Gain

Vopamp -VF

2.5 V - 1.3 V

12 mA

= 100

Ω

R4 =

17096

iil300_19

6.0

5.5

5.0

4.5

4.0

2.25

2.50

2.75

3.00

3.25

3.50

3.75

Vout = 14.4 mV + 0.6036 x Vin

LM 201 Ta = 25°C

Figure 20. Linearity Error vs. Input Voltage

Figure 21. Amplitude and Phase Power Supply Control

iil300_20

6.0

5.5

5.0

4.5

4.0

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

Vin - Input Voltage - V

LM201

iil300_21

PHASE

10 3

10 4

10 5

10 6

-2

-4

-6

-8

-45

-90

-135

-180

F - Frequency - Hz

R3 =

Vref1

IP1

Vref1

K1IFq

17098

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