TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994
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High-Resolution Conversion of Light Intensity to Frequency With No External Components Communicates Directly With a Microcontroller Compact Three-Leaded Clear-Plastic Package
Single-Supply Operation Down to 2.7 V Nonlinearity Error Typically 0.2% at 100 kHz Stable 100 ppm/°C Temperature Coefficient Advanced LinCMOS Technology
description The TSL235 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 it is TTL compatible, the output allows direct interface to a microcontroller or other logic circuitry. The device has been temperature compensated for the ultravioletto-visible light range of 300 nm to 700 nm and responds over the light range of 300 nm to 1100 nm. The TSL235 is characterized for operation over the temperature range of – 25°C to 70°C.
mechanical data The TSL235 is offered in a clear-plastic three-leaded package. 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)
0,635 (0.025) 0,4 (0.016)
Pin 1 Pin 2 Pin 3
1,25 (0.049) 0,75 (0.029)
GND VDD OUT
1 2 4,0 (0.157) T.P.†
3
1 2 2,05 (0.081) 1,55 (0.061)
0,65 (0.026) 0,55 (0.022)
0,86 (0.034) 0,46 (0.018)
15,7 (0.619) 13,2 (0.520)
3,05 (0.120) 2,55 (0.100)
4,8 (0.189) 4,4 (0.173)
4,85 (0.191) 4,35 (0.171) 0,85 (0.033) 0,35 (0.014)
0,75 (0.030) R
0,51 (0.02) 0,385 (0.015)
3
5,05 (0.199) 4,55 (0.179)
1,75 (0.069) 1,25 (0.049)
4,35 (0.171) 3,85 (0.152)
2,74 (0.108) 2,34 (0.092)
† True position when unit is installed. ALL LINEAR DIMENSIONS ARE IN MILLIMETERS AND PARENTHETICALLY IN INCHES
Advanced LinCMOS is a trademark of Texas Instruments Incorporated. Copyright 1994, 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.
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TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994
functional block diagram
Light
Current-to-Frequency Converter
Photodiode
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 25°C to 70°C Storage temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 25°C to 85°C Lead 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, 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 Supply voltage, VDD Operating free-air temperature range, TA
MIN
NOM
2.7
5
– 25
MAX
UNIT
6
V
70
°C
electrical characteristics at VDD = 5 V, TA = 25°C (unless otherwise noted) PARAMETER VOH VOL
High-level output voltage
IDD
Supply current
TEST CONDITIONS IOH = – 4 mA IOL = 4 mA
Low-level output voltage Full-scale frequency‡
MIN 4
TYP
MAX
4.3
V
0.17
0.26
2
3
500
Temperature coefficient of output frequency
λ ≤ 700 nm, –25°C ≤ TA ≤ 70°C
V mA kHz
± 100
kSVS Supply-voltage sensitivity VDD = 5 V ±10% ‡ Full-scale frequency is the maximum operating frequency of the device without saturation.
UNIT
ppm/°C
0.5
%/ V
operating characteristics at VDD = 5 V, TA = 25°C PARAMETER fO
Output frequency
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Ee = 375 µW/cm2, λp = 670 nm
200
250
300
kHz
0.25
10
Ee = 0 fO = 0 kHz to 10 kHz
Nonlinearity §
fO = 0 kHz to 100 kHz
%F.S.
± 0.2%
%F.S.
1 pulse of new frequency plus 1 µs
Step response to full-scale step input
‡ 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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Hz
± 0.1%
TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994
TYPICAL CHARACTERISTICS OUTPUT FREQUENCY vs IRRADIANCE
PHOTODIODE SPECTRAL RESPONSIVITY 1
1000
0.8 Normalized Responsivity
100 fO – Output Frequency – kHz
TA = 25°C
VDD = 5 V λp = 670 nm TA = 25°C
10
1
0.1
0.6
0.4
0.2
0.01
0.001 0.001
0.01
0.1
1
10
10 0
0 300
1k
400
Ee – Irradiance – µW/cm2
500
600
fO(dark) – Dark Frequency – Hz
VDD = 5 V Ee = 0 10
1
0.1
50
75
TA – Temperature – °C
Temperature Coefficient of Output Frequency – ppm/ °C
100
25
1000 1100
Figure 2
DARK FREQUENCY vs TEMPERATURE
0
900
800
λ – Wavelength – nm
Figure 1
0.01 – 25
700
TEMPERATURE COEFFICIENT OF OUTPUT FREQUENCY vs WAVELENGTH OF INCIDENT LIGHT 10000 VDD = 5 V TA = 25°C to 70°C 8000
6000
4000
2000
0 300
400
500
600
700
800
900
1000
λ – Wavelength of Incident Light – nm
Figure 3
Figure 4
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TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994
TYPICAL CHARACTERISTICS OUTPUT FREQUENCY vs SUPPLY VOLTAGE 1.005
Normalized Output Frequency
1.004
TA = 25°C fO = 500 kHz
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
VDD – Supply Voltage – V
Figure 5
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TSL235 LIGHT-TO-FREQUENCY CONVERTER SOES012 – SEPTEMBER 1994
APPLICATION INFORMATION power-supply considerations For optimum device performance, power-supply lines should be decoupled by a 0.01-µF to 0.1-µF capacitor with short leads (see Figure 6).
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 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 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. VDD
0.1 µF 2
TSL235
3
1
Timer / Port
MCU
Figure 6. Typical TSL235 Interface to a Microcontroller
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