TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994••• High-Resolution Conversion of LightIntensity to Frequency With No ExternalComponentsCommunicates Directly With aMicrocontrollerCompact Three-Leaded Clear-PlasticPackage••••Single-Supply Operation Down to 2.7 VNonlinearity Error Typically 0.2% at 100 kHzStable 100 ppm/°C Temperature CoefficientAdvanced LinCMOS™ TechnologydescriptionThe TSL235 light-to-frequency converter combines a silicon photodiode and a current-to-frequency converteron a single monolithic CMOS integrated circuit. The output is a square wave (50% duty cycle) with frequencydirectly proportional to light intensity. Because it is TTL compatible, the output allows direct interface to amicrocontroller or other logic circuitry. The device has been temperature compensated for the ultraviolet-to-visible light range of 300 nm to 700nm and responds over the light range of 300 nm to 1100 nm. The TSL235is characterized for operation over the temperature range of –25°C to 70°C.mechanical dataThe TSL235 is offered in a clear-plastic three-leaded package. The photodiode area is 1.36 mm2 (0.0029 in2).0,75 (0.030)0,65 (0.026)2,25 (0.0)1,75 (0.069)1,25 (0.049)0,75 (0.029)124,0 (0.157) T.P.†32,0 (0.079) T.P.†0,635 (0.025)0,4 (0.016)Pin 1Pin 2Pin 3GNDVDDOUT122,05 (0.081)1,55 (0.061)30,86 (0.034)0,46 (0.018)0,65 (0.026)0,55 (0.022)15,7 (0.619)13,2 (0.520)4,8 (0.1)4,4 (0.173)0,85 (0.033)0,35 (0.014)0,51 (0.02)0,385 (0.015)0,75 (0.030) R3,05 (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.2,74 (0.108)2,34 (0.092)ALL LINEAR DIMENSIONS ARE IN MILLIMETERS AND PARENTHETICALLY IN INCHESAdvanced 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 Instrumentsstandard warranty. Production processing does not necessarily includetesting of all parameters.Copyright © 1994, Texas Instruments IncorporatedPOST OFFICE BOX 655303 DALLAS, TEXAS 75265•1TSL235LIGHT-TO-FREQUENCY CONVERTERSOES012 – SEPTEMBER 1994 functional block diagramCurrent-to-FrequencyConverterLightPhotodiodeOutputabsolute maximum ratings over operating free-air temperature range (unless otherwise noted)†Supply voltage, VDD (see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 VOperating free-air temperature range, TA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –25°C to 70°CStorage temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –25°C to 85°CLead temperature 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260°C†Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, andfunctional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is notimplied. 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 conditionsMINSupply voltage, VDDOperating free-air temperature range, TA2.7–25NOM5MAX670UNITV°Celectrical characteristics at VDD = 5 V, TA = 25°C (unless otherwise noted)PARAMETERVOHVOLIDDHigh-level output voltageLow-level output voltageSupply currentFull-scale frequency‡Temperature coefficient of output frequencyλ ≤ 700 nm, –25°C ≤TA ≤ 70°CkSVSSupply-voltage sensitivityVDD = 5 V ±10%‡Full-scale frequency is the maximum operating frequency of the device without saturation.500±1000.5TEST CONDITIONSIOH = –4 mAIOL = 4 mAMIN4TYP4.30.1720.263MAXUNITVVmAkHzppm/°C%/Voperating characteristics at VDD = 5 V, TA = 25°CPARAMETERfOOutputfrequencyOutput frequencyNonlinearity§Step response to full-scale step inputTEST CONDITIONSEe = 375 µW/cm2, λp = 670 nmEe = 0fO = 0 kHz to 10 kHzfO = 0 kHz to 100 kHzMIN200TYP2500.25±0.1%±0.2%1 pulse of newfrequency plus 1 µsMAX30010UNITkHzHz%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.2POST OFFICE BOX 655303 DALLAS, TEXAS 75265•TSL235LIGHT-TO-FREQUENCY CONVERTERSOES012 – SEPTEMBER 1994TYPICAL CHARACTERISTICSOUTPUT FREQUENCYvsIRRADIANCE1000VDD = 5 Vλp = 670 nmTA = 25°CNormalized Responsivity1TA = 25°C0.8PHOTODIODE SPECTRAL RESPONSIVITY100fO– Output Frequency – kHz100.610.40.10.010.20.0010.0010.010.11101001 k030040050060070080090010001100Ee – Irradiance – µW/cm2λ – Wavelength – nmFigure 1DARK FREQUENCYvsTEMPERATURE100VDD = 5 VEe = 0fO(dark)– Dark Frequency – Hz10Figure 2TEMPERATURE COEFFICIENTOF OUTPUT FREQUENCYvsWAVELENGTH OF INCIDENT LIGHT10000VDD = 5 VTA = 25°C to 70°C8000Temperature Coefficient of Output Frequency – ppm/°C6000140000.120000.01– 25025TA – Temperature – °C507503004005006007008009001000λ – Wavelength of Incident Light – nmFigure 3Figure 4POST OFFICE BOX 655303 DALLAS, TEXAS 75265•3TSL235LIGHT-TO-FREQUENCY CONVERTERSOES012 – SEPTEMBER 1994 TYPICAL CHARACTERISTICSOUTPUT FREQUENCYvsSUPPLY VOLTAGE1.0051.004Normalized Output Frequency1.0031.0021.00110.9990.9980.9970.9960.9952.533.4.555.56TA = 25°CfO = 500 kHzVDD – Supply Voltage – VFigure POST OFFICE BOX 655303 DALLAS, TEXAS 75265•TSL235LIGHT-TO-FREQUENCY CONVERTERSOES012 – SEPTEMBER 1994APPLICATION INFORMATIONpower-supply considerationsFor optimum device performance, power-supply lines should be decoupled by a 0.01-µF to 0.1-µF capacitor withshort leads (see Figure 6).output interfaceThe output of the device is designed to drive a standard TTL or CMOS logic input over short distances. If linesgreater than 12 inches are used on the output, a buffer or line driver is recommended.measuring the frequencyThe choice of interface and measurement technique depends on the desired resolution and data-acquisitionrate. 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 toreference-clock rate. The technique is employed to measure rapidly varying light levels or to make a fastmeasurement of a constant light source.Maximum resolution and accuracy may be obtained using frequency-measurement, pulse-accumulation, orintegration techniques. Frequency measurements provide the added benefit of averaging out random- orhigh-frequency variations (jitter) resulting from noise in the light signal. Resolution is limited mainly by availablecounter registers and allowable measurement time. Frequency measurement is well suited for slowly varyingor constant light levels and for reading average light levels over short periods of time. Integration, theaccumulation of pulses over a very long period of time, can be used to measure exposure – the amount of lightpresent in an area over a given time period.VDD0.1 µF2TSL2353Timer/Port1MCUFigure 6. Typical TSL235 Interface to a MicrocontrollerPOST OFFICE BOX 655303 DALLAS, TEXAS 75265•5IMPORTANT NOTICE
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