TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
1
The LUMENOLOGY r Company r
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Copyright E 2008, TAOS Inc.
www.taosinc.com
DHigh-Resolution Conversion of Light
Intensity to Frequency With No External
Components
DHigh Irradiance Responsivity . . .
2.3 kHz/(W/cm2) at λp = 524 nm
DLow Dark Frequency ...< 2 Hz at 25 C
DSingle-Supply Operation . . . 2.7 V to 5.5 V
DStable 200 ppm/°C Temperature Coefficient
DInterfaces Directly to a Microcontroller
DLead (Pb) Free Package
DRoHS Compliant
Description
The TSL238 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. Output enable (OE) places the output in a high-impedance state for
multiple-unit sharing of a microcontroller input line. 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 TSL238 is characterized for operation over the temperature range of −40°C to 85°C and is supplied in an
8-lead plastic small outline package. When supplied in the lead (Pb) free package, the device is RoHS
compliant.
For automotive and other extended temperature applications, please contact TAOS for information.
Functional Block Diagram
Light Current-to-Frequency
Converter
Photodiode Output
Available Options
DEVICE TAPACKAGE − LEADS PACKAGE DESIGNATOR ORDERING NUMBER
TSL238 −25°C to 70°C8-lead Plastic Small Outline IC D TSL238D
r
r
Texas Advanced Optoelectronic Solutions Inc.
1001 Klein Road S Suite 300 S Plano, TX 75074 S (972) 673-0759
8 OUT
7 VDD
6 GND
5 OE
PACKAGE D
8-LEAD SOIC
(TOP VIEW)
NC 1
NC 2
NC 3
NC 4
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
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Terminal Functions
TERMINAL
NAME D PKG
NO.
TYPE DESCRIPTION
GND 6 Power supply ground. All voltages are referenced to GND.
NC 1, 2, 3 No connection.
NC 4 Substrate. Pin 4 is resistively connected to the substrate of the die, which is at the same potential as pin 6.
Pin 4 must either be connected to pin 6 or left unconnected. Pin 4 cannot be used for a ground connection
by itself.
OE 5 I Enable for fO (active low).
OUT 8 O Output frequency.
VDD 7Supply voltage.
Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted)†
Supply voltage, VDD (see Note 1) 6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage range, VI −0.3 V to VDD +0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Output current, IO ± 5 mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Short circuit of output to ground duration 5 s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range, TA (see Note 2) −40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, Tstg (see Note 2) −40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Solder conditions in accordance with JEDEC J−STD−020A, maximum temperature (see Note 3) 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.
NOTES: 1. All voltage values are with respect to GND.
2. Long-term storage or operation above 70°C could cause package yellowing that will lower the sensitivity to wavelengths < 500nm.
3. The device may be hand soldered provided that heat is applied only to the solder pad and no contact is made between the tip of
the solder iron and the device lead. The maximum time heat should be applied to the device is 5 seconds.
Recommended Operating Conditions
MIN NOM MAX UNIT
Supply voltage, VDD 2.7 5 5.5 V
High-level input voltage, VIH 0.8 × VDD VDD V
Low-level input voltage, VIL 0 0.5 V
Operating free-air temperature range, TA−40 70 °C
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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Electrical Characteristics at VDD = 5 V, TA = 25°C (Note 1) (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VOH High-level output voltage IOH = −1 mA 4 4.5 V
VOL Low-level output voltage IOL = 1 mA 0.25 0.4 V
IIH High-level input current −10 10 μA
IIH Low-level input current −10 10 μA
IDD Supply current Ee = 21.2 μW/cm22 3 mA
Full-scale frequency (Note 2) TA = 50°C (Note 3) 500 1000 kHz
Temperature coefficient of responsivity Wavelength < 600nm, fO = 50 kHz ±200 ppm/°C
kSVS Supply-voltage sensitivity VDD = 5 V ±10% ±0.5 %/ V
NOTES: 1. The input irradiance is supplied with green LED light source with peak wavelength = 524 nm.
2. Full-scale frequency is the maximum frequency of the device without saturation. Higher irradiance will not result in any additional
increase of output frequency. The output frequency will remain at approximately the saturation frequency to a minimum of 1000
μW/sqcm 524-nm irradiance. During production testing, devices are not tested at this very high irradiance level.
3. Measured at wafer probe using 50°C hot chuck.
Operating Characteristics at VDD = 5 V, TA = 25°C, λp = 524 nm (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
fOOutput frequency Ee = 21.2 μW/cm240 50 60 kHz
f
Dark frequency
Ee = 0 μW/cm20 1.2 Hz
fDDark frequency Ee = 0 μW/cm2, TA = 50°C (Note 1) 0 6 Hz
ReIrradiance responsivity 2.3 kHz/(μW/
cm2)
λpPeak response wavelength 700 nm
Nonlinearity (Note 2) fO = 0 kHz to 10 kHz ±1% %F.S.
Step response to full-scale step input 1 pulse of new
frequency plus 1 μs
Time from OE low to output enabled 1 period of output
frequency
NOTES: 1. Measured at wafer probe using 50°C hot chuck.
2. Nonlinearity is defined as the deviation from a straight line between zero and maximum of stated range, expressed as a percent
of stated range.
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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TYPICAL CHARACTERISTICS
1
0.1
0.01
0.001
0.001 0.01 0.1 1 10
10
100
OUTPUT FREQUENCY
vs
IRRADIANCE
100 1 k
Ee − Irradiance − μW/cm2
VDD = 5 V
λp = 524 nm
TA = 25°C
1000
Figure 1 Figure 2
300 400 500 600 700 1000800 900 1100
λ − Wavelength − nm
Normalized Responsivity
PHOTODIODE SPECTRAL RESPONSIVITY
Output Frequency (fO − fD) — kHz
0
0.2
0.4
0.6
0.8
1
Figure 3
SUPPLY CURRENT
vs.
FREE-AIR TEMPERATURE
IDD — Supply Current — mA
TA − Free-Air Temperature − °C
0
0.4
0.8
1.2
1.6
2.0
−25 0 25 50 75
Figure 4
OUTPUT FREQUENCY
vs.
FREE-AIR TEMPERATURE
TA − Free-Air Temperature − °C
fO — Output Frequency — Normalized
0.500
0.600
0.700
0.800
0.900
1.000
1.100
1.200
−25 0 25 50 75
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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TYPICAL CHARACTERISTICS
Figure 5
NORMALIZED OUTPUT FREQUENCY
vs.
ANGULAR DISPLACEMENT
− Angular Displacement − °
fO — Output Frequency — Normalized
0
0.2
0.4
0.6
0.8
1
−90 −60 −30 0 30 60 90
Optical Axis
Angular Displacement is
Equal for Both Aspects
Figure 6
DARK FREQUENCY
vs.
FREE-AIR TEMPERATURE
fD — Dark Frequency — Hz
TA − Free-Air Temperature − °C
−7.5
−4.5
−1.5
1.5
4.5
7.5
−25 −5 15 35 55 75
−6.0
−3.0
0.0
3.0
6.0
NOTE A
NOTE A: Internal offsets that result in dark frequency can be both positive and negative. The dashed line represents the case of negative offset
in which an equivalent amount of light signal is required to obtain a non-zero output frequency.
Figure 7
λ − Wavelength of Incident Light − nm
PHOTODIODE RESPONSIVITY TEMPERATURE
COEFFICIENT vs.
WAVELENGTH OF INCIDENT LIGHT
1k
2k
3k
4k
5k
6k
7k
8k
9k
10k
0
11k
Temperature Coefficient — ppm/degC
600 650 700 750 800 850 900 950 1000
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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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
TSL238 (Figure 8). A low-noise power supply is required to minimize jitter on output pulse.
TSL238 Timer / Port
MCU
0.1 μF
VDD
VDD
OUT
GND
Figure 8. Typical TSL238 Interface to a Microcontroller
Device Operational Details
The frequency at the output pin (OUT) is given by:
fO = fD + (Re) (Ee)
where:
fOis the output frequency
fDis the output frequency for dark condition (Ee = 0)
Reis the device responsivity for a given wavelength of light given in kHz/(μW/cm2)
Eeis the incident irradiance in μW/cm2
fD is a constant error term in the output frequency calculation resulting from leakage currents, and is
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).
Output Interface
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.
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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APPLICATION INFORMATION
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 the
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.
Output enable (OE) places the output in a high-impedance state for multiple-unit sharing of a microcontroller
input line. When the OE line goes low, the device resynchronizes the output to an integration cycle. The rising
edge of the output signal (OUT) will occur exactly one period of the output frequency after OE goes low.
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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Copyright E 2008, TAOS Inc. The LUMENOLOGY r Company
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MECHANICAL DATA
This SOIC package consists of an integrated circuit mounted on a lead frame and encapsulated with an electrically
nonconductive clear plastic compound having an index of refraction of 1.55.
PACKAGE D PLASTIC SMALL-OUTLINE
A
1.75
1.35
0.50
0.25
4.00
3.80
6.20
5.80
450.88 TYP TOP OF
SENSOR DIE
5.00
4.80
5.3
MAX
1.27
0.41 0.25
0.10
0.25
0.19
DETAIL A
PIN 1
6 1.27 0.510
0.330
8
2.8 TYP
CLEAR WINDOW
NOTE B
PIN 1
TOP VIEW BOTTOM VIEW
SIDE VIEW
END VIEW
Lead Free
Pb
NOTES: A. All linear dimensions are in millimeters.
B. The center of the 0.84-mm by 0.84-mm photo-active area is located in the center of the package ± 0.25 mm.
C. Pin 4 is resistively coupled to the substrate of the die, which is at the same potential as Pin 6. Pin 4 must either be connected to
Pin 6 or left unconnected. Pin 4 cannot be used as the sole ground connection.
D. Leads are plated with Pd (min 0.1 μ inch) + Ni (min 10 μ inch) + Au (min 0.1 μ inch).
E. This drawing is subject to change without notice.
Figure 9. Package D — Plastic Small Outline IC Packaging Configuration
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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MECHANICAL DATA
0.292 0.013
[0.0115 0.0005]
2.11 0.10 [0.083 0.004]
2 0.05
[0.079
0.002]
4 0.1
[0.157
0.004]
1.75 0.10
[0.069 0.004]
12 + 0.3 − 0.1
[0.472 + 0.12 − 0.004]
SIDE VIEW
TOP VIEW END VIEW
DETAIL B
5.50 0.05
[0.217 0.002]
8 0.1
[0.315
0.004]
1.50
B
B
AA
6.45 0.10
[0.254 0.004]
5.13 0.10
[0.202 0.004]
DETAIL A
AoBo
Ko
NOTES: A. All linear dimensions are in millimeters [inches].
B. The dimensions on this drawing are for illustrative purposes only. Dimensions of an actual carrier may vary slightly.
C. Symbols on drawing Ao, Bo, and Ko are defined in ANSI EIA Standard 481−B 2001.
D. Each reel is 178 millimeters in diameter and contains 1000 parts.
E. TAOS packaging tape and reel conform to the requirements of EIA Standard 481−B.
F. This drawing is subject to change without notice.
Figure 10. Package D Carrier Tape
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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MANUFACTURING INFORMATION
The Plastic Small Outline IC package (D) has been tested and has demonstrated an ability to be reflow soldered
to a PCB substrate.
The solder reflow profile describes the expected maximum heat exposure of components during the solder
reflow process of product on a PCB. Temperature is measured on top of component. The component should
be limited to a maximum of three passes through this solder reflow profile.
Table 1. TSL238 Solder Reflow Profile
PARAMETER REFERENCE TSL238
Average temperature gradient in preheating 2.5°C/sec
Soak time tsoak 2 to 3 minutes
Time above 217°C t1Max 60 sec
Time above 230°C t2Max 50 sec
Time above Tpeak −10°C t3Max 10 sec
Peak temperature in reflow Tpeak 260° C (−0°C/+5°C)
Temperature gradient in cooling Max −5°C/sec
t3
t2
t1
tsoak
T3
T2
T1
Tpeak
Not to scale — for reference only
Time (sec)
Temperature (C)
Figure 11. Solder Reflow Profile Graph
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
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Moisture Sensitivity
Optical characteristics of the device can be adversely affected during the soldering process by the release and
vaporization of moisture that has been previously absorbed into the package molding compound. To prevent
these adverse conditions, all devices shipped in carrier tape have been pre-baked and shipped in a sealed
moisture-barrier bag. No further action is necessary if these devices are processed through solder reflow within
24 hours of the seal being broken on the moisture-barrier bag.
However, for all devices shipped in tubes or if the seal on the moisture barrier bag has been broken for 24 hours
or longer, it is recommended that the following procedures be used to ensure the package molding compound
contains the smallest amount of absorbed moisture possible.
For devices shipped in tubes:
1. Remove devices from tubes
2. Bake devices for 4 hours, at 90°C
3. After cooling, load devices back into tubes
4. Perform solder reflow within 24 hours after bake
Bake only a quantity of devices that can be processed through solder reflow in 24 hours. Devices can be
re-baked for 4 hours, at 90°C for a cumulative total of 12 hours (3 bakes for 4 hours at 90°C).
For devices shipped in carrier tape:
1. Bake devices for 4 hours, at 90°C in the tape
2. Perform solder reflow within 24 hours after bake
Bake only a quantity of devices that can be processed through solder reflow in 24 hours. Devices can be
re−baked for 4 hours in tape, at 90°C for a cumulative total of 12 hours (3 bakes for 4 hours at 90°C).
TSL238
HIGH-SENSITIVITY
LIGHT-TO-FREQUENCY CONVERTER
TAOS073J − SEPTEMBER 2008
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PRODUCTION DATA — information in this document is current at publication date. Products conform to
specifications in accordance with the terms of Texas Advanced Optoelectronic Solutions, Inc. standard
warranty. Production processing does not necessarily include testing of all parameters.
LEAD-FREE (Pb-FREE) and GREEN STATEMENT
Pb-Free (RoHS) TAOS’ terms Lead-Free or Pb-Free mean semiconductor products that are compatible with the current
RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous
materials. Where designed to be soldered at high temperatures, TAOS Pb-Free products are suitable for use in specified
lead-free processes.
Green (RoHS & no Sb/Br) TAOS defines Green to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and
Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material).
Important Information and Disclaimer The information provided in this statement represents TAOS’ knowledge and
belief as of the date that it is provided. TAOS bases its knowledge and belief on information provided by third parties,
and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate
information from third parties. TAOS has taken and continues to take reasonable steps to provide representative
and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and
chemicals. TAOS and TAOS suppliers consider certain information to be proprietary, and thus CAS numbers and other
limited information may not be available for release.
NOTICE
Texas Advanced Optoelectronic Solutions, Inc. (TAOS) reserves the right to make changes to the products contained in this
document to improve performance or for any other purpose, or to discontinue them without notice. Customers are advised
to contact TAOS to obtain the latest product information before placing orders or designing TAOS products into systems.
TAOS assumes no responsibility for the use of any products or circuits described in this document or customer product
design, conveys no license, either expressed or implied, under any patent or other right, and makes no representation that
the circuits are free of patent infringement. TAOS further makes no claim as to the suitability of its products for any particular
purpose, nor does TAOS assume any liability arising out of the use of any product or circuit, and specifically disclaims any
and all liability, including without limitation consequential or incidental damages.
TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS, INC. PRODUCTS ARE NOT DESIGNED OR INTENDED FOR
USE IN CRITICAL APPLICATIONS IN WHICH THE FAILURE OR MALFUNCTION OF THE TAOS PRODUCT MAY
RESULT IN PERSONAL INJURY OR DEATH. USE OF TAOS PRODUCTS IN LIFE SUPPORT SYSTEMS IS EXPRESSLY
UNAUTHORIZED AND ANY SUCH USE BY A CUSTOMER IS COMPLETELY AT THE CUSTOMER’S RISK.
LUMENOLOGY, TAOS, the TAOS logo, and Texas Advanced Optoelectronic Solutions are registered trademarks of Texas Advanced
Optoelectronic Solutions Incorporated.
