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TSL245 INFRARED LIGHT-TO-FREQUENCY CONVERTER
SOES018 - MAY 1995
D D D
High-Resolution Conversion of Light Intensity to Frequency With No External Components Direct Interface With a Microcontroller Compact Three-Leaded Plastic Package
D D D D
Single-Supply Operation Down to 2.7 V Nonlinearity Error Typically 0.2% at 100 kHz Advanced LinCMOSTM Technology Integral Visible-Light Cutoff Filter
description
The TSL245 infrared light-to-frequency converter combines a silicon photodiode and a current-to-frequency converter on a single monolithic CMOS integrated circuit. The output is a square wave (50% duty cycle) with frequency directly proportional to light intensity. Because the output is TTL compatible, it allows direct interface to a microcontroller or other logic circuitry. The device responds over the infrared light range of 800 nm to 1100 nm. The TSL245 is characterized for operation over the temperature range of - 25C to 70C. The TSL245 is offered in a black, infrared-transmissive package (see Figure 1). The photodiode area is 1.36 mm2 (0.0029 in2).
2,0 (0.079) T.P.
0,75 (0.030) 0,65 (0.026)
2,25 (0.089) 1,75 (0.069) 1,25 (0.049) 0,75 (0.030)
0,635 (0.025) 0,4 (0.016) 1 2 4,0 (0.157) T.P. 3
Pin 1 Pin 2 Pin 3
GND VDD OUT
1 2 2,05 (0.081) 1,55 (0.061) 3
0,86 (0.034) 0,46 (0.018)
0,65 (0.026) 0,55 (0.022) 15,7 (0.619) 13,2 (0.520) 4,8 (0.189) 4,4 (0.173) 0,85 (0.033) 0,35 (0.014) 0,51 (0.02) 0,385 (0.015) 0,75 (0.030) R
3,05 (0.120) 2,55 (0.100) 4,85 (0.191) 4,35 (0.171) 1,75 (0.069) 1,25 (0.049) 4,35 (0.171) 3,85 (0.152)
5,05 (0.199) 4,55 (0.179) True position when unit is installed. NOTE A: All linear dimensions are in millimeters and parenthetically in inches.
2,74 (0.108) 2,34 (0.092)
Figure 1. TSL245 Packaging Configuration
Advanced LinCMOS is a trademark of Texas Instruments Incorporated.
PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters.
Copyright (c) 1995, Texas Instruments Incorporated
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
1
TSL245 INFRARED LIGHT-TO-FREQUENCY CONVERTER
SOES018 - MAY 1995
functional block diagram
Light
Photodiode
Current-to-Frequency Converter
Output
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
Supply voltage, VDD (see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 V Operating free-air temperature range, TA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 25C to 70C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 25C to 85C Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260C
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. NOTE 1: All voltage values are with respect to GND.
recommended operating conditions
MIN Supply voltage, VDD Operating free-air temperature range, TA 2.7 - 25 NOM 5 MAX 6 70 UNIT V C
electrical characteristics at VDD = 5 V, TA = 25C (unless otherwise noted)
PARAMETER VOH VOL IDD High-level output voltage Low-level output voltage Supply current Full-scale frequency kSVS Supply-voltage sensitivity VDD = 5 V 10% Full-scale frequency is the maximum operating frequency of the device without saturation. 500 0.5 TEST CONDITIONS IOH = - 4 mA IOL = 4 mA MIN 4 TYP 4.3 0.17 2 0.26 3 MAX UNIT V V mA kHz %/ V
operating characteristics at VDD = 5 V, TA = 25C
PARAMETER fO Output frequency Nonlinearity Step response to full-scale step input TEST CONDITIONS Ee = 920 W/cm2, p = 940 nm Ee = 0 fO = 0 kHz to 10 kHz fO = 0 kHz to 100 kHz MIN 200 TYP 250 0.25 0.1% 0.2% 1 pulse of new frequency plus 1 s MAX 300 10 UNIT kHz Hz %F.S. %F.S.
Full-scale frequency is the maximum operating frequency of the device without saturation. Nonlinearity is defined as the deviation of fO from a straight line between zero and full scale, expressed as a percent of full scale.
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POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
TSL245 INFRARED LIGHT-TO-FREQUENCY CONVERTER
SOES018 - MAY 1995
TYPICAL CHARACTERISTICS
OUTPUT FREQUENCY vs IRRADIANCE
1000 VDD = 5 V p = 940 nm TA = 25C Normalized Responsivity 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.001 0.001 0.01 0.1 1 10 10 0 1k 0 600 700 800 900 1000 1100 TA = 25C
PHOTODIODE SPECTRAL RESPONSIVITY
100 fO - Output Frequency - kHz
10
1
0.1
0.01
Ee - Irradiance - W/cm2
- Wavelength - nm
Figure 2
Figure 3
TEMPERATURE COEFFICIENT OF OUTPUT FREQUENCY vs WAVELENGTH OF INCIDENT LIGHT
10000 VDD = 5 V TA = 25C to 70C 8000
100 VDD = 5 V Ee = 0 fO(dark) - Dark Frequency - Hz 10
Temperature Coefficient of Output Frequency - ppm/ C
DARK FREQUENCY vs TEMPERATURE
6000
1
4000
0.1
2000
0.01 - 25
0
25 TA - Temperature - C
50
75
0 700
750
800
850
900
950
1000
- Wavelength of Incident Light - nm
Figure 4
Figure 5
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
3
TSL245 INFRARED LIGHT-TO-FREQUENCY CONVERTER
SOES018 - MAY 1995
TYPICAL CHARACTERISTICS
OUTPUT FREQUENCY vs SUPPLY VOLTAGE
1.005 1.004 Normalized Output Frequency 1.003 1.002 1.001 1 0.999 0.998 0.997 0.996 0.995 2.5 3 3.5 4 4.5 5 5.5 6 TA = 25C fO = 500 kHz
VDD - Supply Voltage - V
Figure 6
4
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
TSL245 INFRARED LIGHT-TO-FREQUENCY CONVERTER
SOES018 - MAY 1995
APPLICATION INFORMATION power-supply considerations
For optimum device performance, power-supply lines should be decoupled by a 0.01-F to 0.1-F capacitor with short leads (see Figure 7).
output interface
The output of the device is designed to drive a standard TTL or CMOS logic input over short distances. If lines greater than 12 inches are used on the output, a buffer or line driver is recommended.
measuring the frequency
The choice of interface and measurement techniques depends on the desired resolution and data-acquisition rate. For maximum data-acquisition rate, period-measurement techniques should be used. Period measurement requires using a fast reference clock with available resolution directly related to reference clock rate. The technique measures rapidly varying light levels or provides a fast measurement of a constant light source. Maximum resolution and accuracy can be obtained using frequency-measurement, pulse-accumulation, or integration techniques. Frequency measurements provide the added benefit of averaging random- or high-frequency variations (jitter) resulting from noise in the light signal. Resolution is limited primarily 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.
VDD
0.1 F 2
TSL245
3
Timer / Port
1
MCU
Figure 7. Typical TSL245 Interface to a Microcontroller
POST OFFICE BOX 655303
* DALLAS, TEXAS 75265
5
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Copyright (c) 1998, Texas Instruments Incorporated

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