®

OPT202

7

some degree, the OPT202 op amp circuitry is designed to

minimize this effect. Sensitive junctions are shielded with

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 OPT202 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.”

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required to operate the

OPT202. 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.

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 OPT202’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. Placing the external resistor in parallel with the

internal resistor requires the DIP package. These connections

take advantage of on-chip capacitive guarding of the internal

resistor, which improves dynamic performance. For values

of R

eliminates gain peaking and prevents instability. The value

LIGHT SOURCE POSITIONING

The OPT202 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

to light intensity

(radiant power).

FIGURE 1. Basic Circuit Connections.

1M

Ω

(Pin available on DIP only)

OPT202

3pF

175

Ω

V

O

–15V

+15V

0.1µF 0.1µF

V

R

F

I

D

I

D

(0V)

λ

FIGURE 2. Using External Feedback Resistor.

100M

Ω

(1)

10M

Ω

(1)

1M

Ω

(1)

330k

Ω

2pF

≤100kΩ

(2)

Not recommended due to possible

op amp instability.

1M

Ω

OPT202

3pF

175

Ω

83

5

4

1

V

Circuit Requires

DIP Package

V–

λ

V+

R

EXT

C

EXT

R

For R

1M

Ω

OPT202

175

Ω

V

V–

λ

V+

R

For R

R

EXT

2