tsl238 TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS, tsl238 Datasheet - Page 6

• Manufacturer Part Number: tsl238
• Description: High-sensitivity Light-to-frequency Converter
• Manufacturer: TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS

TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073F − OCTOBER 2007
Power-Supply Considerations
Device Operational Details
Output Interface
6
Copyright E 2007, TAOS Inc.
Power-supply lines must be decoupled by a 0.01-μF to 0.1-μF capacitor with short leads placed close to the
TSL238 (Figure 7). A low-noise power supply is required to minimize jitter on output pulse.
The frequency at the output pin (OUT) is given by:
where:
f
independent of light intensity. The TSL238 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).
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.
D
is a constant error term in the output frequency calculation resulting from leakage currents, and is
f
f
R
E
O
D
e
e
is the output frequency
is the output frequency for dark condition (E
is the device responsivity for a given wavelength of light given in kHz/(μW/cm
is the incident irradiance in μW/cm
0.1 μF
Figure 7. Typical TSL238 Interface to a Microcontroller
f
O
= f
GND
APPLICATION INFORMATION
TSL238
D
r
V
+ (R
DD
V
DD
e
) (E
www.taosinc.com
2
e
)
OUT
e
= 0)
Timer / Port
MCU
r
The LUMENOLOGY r Company
2
)