TSL237T

HIGH-SENSITIVITY

LIGHT-TO-FREQUENCY CONVERTER

TAOS055J − DECEMBER 2007

5

The LUMENOLOGY r Company

r

r

Copyright E 2007, TAOS Inc.

www.taosinc.com

APPLICATION INFORMATION

Power-Supply Considerations

Power-supply lines must be decoupled by a 0.01-μF to 0.1-μF capacitor with short leads placed close to the

TSL237T (Figure 9). A low-noise power supply is required to minimize jitter on output pulse.

TSL237T

Timer / Port

MCU

0.1 μF

OUT

GND

OE

Figure 9. Typical TSL237T Interface to a Microcontroller

Device Operational Details

The frequency at the output pin (OUT) is given by:

where:

is the output frequency

independent of light intensity. The TSL237T die is trimmed to minimize the magnitude of this dark frequency

component so that it can be neglected in the transfer function calculation. In many applications, measurement

of the actual dark frequency may be impractical due to measurement times ranging from several seconds to

several minutes, and the fact that some devices may never transition (zero dark frequency).

Input Interface

A low-impedance electrical connection between the device OE terminal and the device GND terminal is required

for improved noise immunity.

Output Interface

The output of the device is designed to drive a CMOS logic input over short distances. If lines greater than 12

inches in length are used on the output, a buffer or line driver is recommended.