TSL238T
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS080E
−
JUNE 2007
APPLICATION INFORMATION
Measuring the Frequency
The choice of interface and measurement technique depends on the desired resolution and data-acquisition
rate. For maximum data-acquisition rate, period-measurement techniques are used.
Period measurement requires the use of a fast reference clock with available resolution directly related to the
reference-clock rate. The technique is employed to measure rapidly varying light levels or to make a fast
measurement of a constant light source.
Maximum resolution and accuracy may be obtained using frequency-measurement, pulse-accumulation,
or integration techniques. Frequency measurements provide the added benefit of averaging out random- or
high-frequency variations (jitter) resulting from noise in the light signal. Resolution is limited mainly by available
counter registers and allowable measurement time. Frequency measurement is well suited for slowly varying
or constant light levels and for reading average light levels over short periods of time. Integration, the
accumulation of pulses over a very long period of time, can be used to measure exposure — the amount of light
present in an area over a given time period.
PCB Pad Layout
Suggested PCB pad layout guidelines for the T package are shown in Figure 9.
2.90
1.50
1.00
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
0.90
Figure 9. Suggested T Package PCB Layout
Copyright
E
2007, TAOS Inc.
r
r
The
LUMENOLOGY
r
Company
6
www.taosinc.com
TAOS [ TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS ]
