r
r
TSL235R
LIGHT-TO-FREQUENCY CONVERTER
TAOS038E
−SEPTEMBER
2007
D
High-Resolution Conversion of Light
D
D
D
D
D
D
D
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 150 ppm/°C Temperature Coefficient
Single-Supply Operation
RoHS Compliant (−LF Package Only)
PACKAGE S
SIDELOOKER
(FRONT VIEW)
PACKAGE SM
SURFACE MOUNT
SIDELOOKER
(FRONT VIEW)
1
GND
2
V
DD
3
OUT
Description
1
GND
2
V
DD
3
OUT
The TSL235R light-to-frequency converter combines a silicon photodiode and a current-to-frequency converter
on a single monolithic CMOS integrated circuit. Output is a square wave (50% duty cycle) with frequency directly
proportional to light intensity (irradiance) on the photodiode. The digital output allows direct interface to a
microcontroller or other logic circuitry. The device has been temperature compensated for the
ultraviolet-to-visible light range of 320 nm to 700 nm and responds over the light range of 320 nm to 1050 nm.
The TSL235R is characterized for operation over the temperature range of
−25°C
to 70°C and is supplied in
a 3-lead clear plastic side-looker package with an integral lens. When supplied in the lead (Pb) free package,
the device is RoHS compliant.
Functional Block Diagram
Current-to-Frequency
Converter
Light
Photodiode
Output
Available Options
DEVICE
TSL235R
TSL235R
TSL235R
T
A
−25°C
to 70°C
−25°C
to 70°C
−25°C
to 70°C
PACKAGE
−
LEADS
3-lead Sidelooker
3-lead Sidelooker—Lead (Pb) Free
3-lead Surface-Mount Sidelooker—Lead (Pb) Free
PACKAGE DESIGNATOR
S
S
SM
ORDERING NUMBER
TSL235R
TSL235R−LF
TSL235RSM−LF
Terminal Functions
TERMINAL
NAME
GND
OUT
V
DD
NO.
1
3
2
O
TYPE
DESCRIPTION
Power supply ground (substrate). All voltages are referenced to GND.
Output frequency.
Supply voltage.
The
LUMENOLOGY
r
Company
Texas Advanced Optoelectronic Solutions Inc.
1001 Klein Road
S
Suite 300
S
Plano, TX 75074
S
(972) 673-0759
r
www.taosinc.com
1
r
Copyright
E
2007, TAOS Inc.
TSL235R
LIGHT-TO-FREQUENCY CONVERTER
TAOS038E
−SEPTEMBER
2007
Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted)
†
Supply voltage, V
DD
(see Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 V
Operating free-air temperature range, T
A
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−25°C
to 70°C
Storage temperature range, T
stg
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−25°C
to 85°C
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds (S Package) . . . . . . . . . . . . . . . . . . . . 260°C
Reflow solder, in accordance with J-STD-020C or J-STD-020D (SM Package) . . . . . . . . . . . . . . . . . . . 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
MIN
Supply voltage, V
DD
Operating free-air temperature range, T
A
2.7
−25
NOM
5
MAX
5.5
70
UNIT
V
°C
Electrical Characteristics at V
DD
= 5 V, T
A
= 25°C (unless otherwise noted)
PARAMETER
V
OH
V
OL
I
DD
High-level output voltage
Low-level output voltage
Supply current
Full-scale
k
SVS
‡
TEST CONDITIONS
I
OH
=
−
4 mA
I
OL
= 4 mA
MIN
4
TYP
4.5
0.25
2
MAX
0.4
3
UNIT
V
V
mA
kHz
ppm/°C
%/ V
frequency
‡
Wavelength < 700nm
V
DD
= 5 V
±10%
500
±
150
±
0.5
Temperature coefficient of output frequency
Supply-voltage sensitivity
Full-scale frequency is the maximum operating frequency of the device without saturation.
Operating Characteristics at V
DD
= 5 V, T
A
= 25°C
PARAMETER
f
O
Output frequency
Nonlinearity
§
N li
it
Step response to full-scale step input
‡
§
TEST CONDITIONS
E
e
= 430
μW/cm
2
,
λ
p
= 635 nm
E
e
= 0
μW/cm
2
f
O
= 0 kHz to 10 kHz
f
O
= 0 kHz to 100 kHz
MIN
200
TYP
250
0.4
±
0.1%
±
0.2%
MAX
300
10
UNIT
kHz
Hz
%F.S.
%F.S.
1 pulse of new
frequency plus 1
μs
Full-scale frequency is the maximum operating frequency of the device without saturation.
Nonlinearity is defined as the deviation of f
O
from a straight line between zero and full scale, expressed as a percent of full scale.
Copyright
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2007, TAOS Inc.
r
r
The
LUMENOLOGY
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Company
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TSL235R
LIGHT-TO-FREQUENCY CONVERTER
TAOS038E
−SEPTEMBER
2007
TYPICAL CHARACTERISTICS
OUTPUT FREQUENCY
vs
IRRADIANCE
1000
V
DD
= 5 V
λ
p
= 635 nm
T
A
= 25°C
Normalized Responsivity
1.2
PHOTODIODE SPECTRAL RESPONSIVITY
f
O
— Output Frequency — kHz
100
1.0
10
0.8
1
0.6
0.1
0.4
0.01
0.2
0.001
0.001
0.01
0.1
1
10
μW/cm
2
10 0
1k
0
300
400
500
E
e
−
Irradiance
−
600 700 800 900
λ
−
Wavelength
−
nm
1000 1100
Figure 1
DARK FREQUENCY
vs
TEMPERATURE
1.2
V
DD
= 5 V
E
e
= 0
Figure 2
TEMPERATURE COEFFICIENT
OF OUTPUT FREQUENCY
vs
WAVELENGTH OF INCIDENT LIGHT
7000
6000
5000
4000
3000
2000
1000
0
300
V
DD
= 5 V
1
f
O(dark)
— Dark Frequency — Hz
0.8
0.6
0.4
0.2
0
−25
0
25
50
T
A
−
Temperature
−
°C
75
Temperature Coefficient of Output Frequency — ppm/5C
400
500
600
700
800
900
1000
λ
−
Wavelength of Incident Light
−
nm
Figure 3
Figure 4
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LUMENOLOGY
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Copyright
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2007, TAOS Inc.
www.taosinc.com
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TSL235R
LIGHT-TO-FREQUENCY CONVERTER
TAOS038E
−SEPTEMBER
2007
TYPICAL CHARACTERISTICS
OUTPUT FREQUENCY
vs
SUPPLY VOLTAGE
1.010
T
A
= 25°C
f
O
= 250 kHz
1.005
Normalized Output Frequency
1.000
0.995
0.990
0.985
0.980
2.5
3
3.5
4
4.5
5
5.5
V
DD
−
Supply Voltage
−
V
Figure 5
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2007, TAOS Inc.
r
r
The
LUMENOLOGY
r
Company
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TSL235R
LIGHT-TO-FREQUENCY CONVERTER
TAOS038E
−SEPTEMBER
2007
APPLICATION INFORMATION
Power-supply considerations
Power-supply lines must be decoupled by a 0.01-μF to 0.1-μF capacitor with short leads placed close to the
TSL235R (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.
V
DD
2
0.1
μF
TSL235R
3
Timer / Port
1
MCU
Figure 6. Typical TSL235R Interface to a Microcontroller
The
LUMENOLOGY
r
Company
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r
Copyright
E
2007, TAOS Inc.
www.taosinc.com
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