7

®

OPT209

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required to operate the

OPT209. Applications with high-impedance power supplies

may require decoupling capacitors located close to the

device pins as shown. Output is zero volts with no light and

increases with increasing illumination.

metal, and differential stages are cross-coupled. Furthermore,

the photodiode area is very large relative to the op amp input

circuitry making these effects negligible.

If your light source is focused to a small area, be sure that

it is properly aimed to fall on the photodiode. If a narrowly

focused light source were to miss the photodiode area and

fall only on the op amp circuitry, the OPT209 would not

perform properly. The large (0.090 x 0.090 inch) photodiode

area allows easy positioning of narrowly focused light sources.

The photodiode area is easily visible—it appears very dark

compared to the surrounding active circuitry.

The incident angle of the light source also affects the

apparent sensitivity in uniform irradiance. For small incident

angles, the loss in sensitivity is simply due to the smaller

effective light gathering area of the photodiode (proportional

to the cosine of the angle). At a greater incident angle, light

is diffused by the side of the package. These effects are

shown in the typical performance curve “Response vs Incident

Angle.”

Photodiode current, I

or flux (in watts) falling on the photodiode. At a wavelength

of 650nm (visible red) the photodiode Responsivity, R

approximately 0.45A/W. Responsivity at other wavelengths

is shown in the typical performance curve “Responsivity vs

Wavelength.”

The typical performance curve “Output Voltage vs Radiant

Power” shows the response throughout a wide range of

radiant power. The response curve “Output Voltage vs

The OPT209’s voltage output is the product of the photodiode

current times the feedback resistor, (I

feedback resistor is laser trimmed to 1M

Ω ±2%. Using this

resistor, the output voltage responsivity, R

0.45V/

µW at 650nm wavelength.

An external resistor can be connected to set a different

voltage responsivity. Best dynamic performance is achieved

Figure 2. These connections take advantage of on-chip

capacitive guarding of the internal resistor, which improves

dynamic performance. For values of R

with R

read from the table in Figure 2.

LIGHT SOURCE POSITIONING

The OPT209 is 100% tested with a light source that uniformly

illuminates the full area of the integrated circuit, including

the op amp. Although all IC amplifiers are light-sensitive to

some degree, the OPT209 op amp circuitry is designed to

minimize this effect. Sensitive junctions are shielded with

to light intensity

(radiant power).

1M

Ω

OPT209

10pF

175

Ω

2

83

5

4

1

V

O

–15V

+15V

0.1µF 0.1µF

V

R

F

I

D

I

D

(0V)

λ

FIGURE 1. Basic Circuit Connections.

FIGURE 2. Using External Feedback Resistor.

100M

Ω

(1)

10M

Ω

(1)

1M

Ω

(1)

330k

Ω

100k

Ω

9pF

33k

Ω

25pF

≤20kΩ

(2)

Not recommended due to possible

op amp instability.

1M

Ω

OPT209

3pF

175

Ω

83

5

4

1

V

V–

λ

V+

R

EXT

C

EXT

2

R

For R

1M

Ω

OPT209

175

Ω

5

4

V

V–

λ

V+

2

R

For R

R

EXT