ams Datasheet Page 1
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TSL238T
High-Sensitivity Light-to-Frequency
Converter
The TSL238T 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 TSL238T is characterized for operation over the
temperature range of -40°C to 85°C and is supplied in a compact
4-lead surface-mount package that is lead (Pb) free and RoHS
compliant.
Ordering Information and Content Guide appear at end of
datasheet.
Key Benefits & Features
The benefits and features of TSL238T, High-Sensitivity
Light-to-Frequency Converter are listed below:
Figure 1:
Added Value Of Using TSL238T
•High-Resolution Conversion of Light Intensity to
Frequency With No External Components
•High Irradiance Responsivity 3.4kHz/(μW/cm2) at
λp=640nm
•Single-Supply Operation 2.7 V to 5.5 V
•Stable 200 ppm/°C Temperature Coefficient
•Interfaces Directly to a Microcontroller
Benefits Features
•Detects Light Intensity at a High Resolution •850K:1 Input Dynamic Range
•Provides Low Light Level Operation •Low Dark Frequency <6Hz at 50oC
•Reduces Board Space Requirements While
Simplifying Designs •2.6mm x 3.8mm 4-Lead SMD (T) Package
General Description
Page 2 ams Datasheet
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TSL238T − General Description
Functional Block Diagram
The functional blocks of this device are shown below:
Figure 2:
TSL238T Block Diagram
Light Current-to-Frequency
Converter
Photodiode Output
ams Datasheet Page 3
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TSL238T − Pin Assignments
Figure 3:
Package T 4-Lead SMD (Top View)
Figure 4:
Terminal Functions
Terminal
Type Description
Name T PKG
No.
GND 2 Power supply ground (substrate). All voltages are referenced to GND.
OE 1I Enable for f
O (active low).
OUT 4 O Output frequency.
VDD 3Supply voltage.
Pin Assignments
OE 1
GND 2
4 OUT
3 VDD
Page 4 ams Datasheet
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TSL238T − Absolute Maximum Ratings
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.
Figure 5:
Absolute Maximum Ratings Over Operating Free-Air Temperature Range (unless otherwise noted)
Note(s):
1. All voltages 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.
Figure 6:
Recommended Operating Conditions
Symbol Parameter Min Max Units
VDD Supply voltage (1) 6V
VIInput voltage range -0.3 VDD+0.3 V
IOOutput current ±5 mA
Short circuit of output to ground duration 5 s
TAOperating free-air temperature range (2) -40 85 °C
Tstg Storage temperature range (2) -40 85 °C
Solder conditions in accordance with JEDEC
J-STD-020C 260 °C
Symbol Parameter Min Nom Max Units
VDD Supply voltage 2.7 5 5.5 V
VIH High-level input voltage 0.8 × VDD VDD V
VIL Low-level input voltage 0 0.5 V
TAOperating free-air temperature range -40 70 °C
Absolute Maximum Ratings
ams Datasheet Page 5
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TSL238T − Electrical Characteristics
Figure 7:
Electrical Characteristics at VDD = 5 V, TA = 25°C, λp = 640nm(1) (unless otherwise noted)
Note(s):
1. The input irradiance is supplied with red LED light source with peak wavelength = 640 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/cm2 640nm irradiance. During production testing, devices are not tested at this very high irradiance level.
3. Measured at wafer probe using 50°C hot chuck.
Symbol Parameter Test Conditions Min Typ Max Unit
VOH High-level output voltage IOH = -1 mA 44.5 V
VOL Low-level output voltage IOL = 1 mA 0.25 0.4 V
IIH High-level input current -10 10 μA
IIL Low-level input current -10 10 μA
IDD Supply current Ee = 14.7 μW/cm2 23mA
Full-scale frequency (2) TA = 50°C (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
Electrical Characteristics
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TSL238T − Electrical Characteristics
Figure 8:
Operating Characteristics at VDD = 5 V, TA = 25°C, λp = 640 nm (unless otherwise noted)
Note(s):
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.
Symbol Parameter Test Conditions Min Typ Max Unit
fO Output frequency Ee = 14.7 μW/cm2 40 50 60 kHz
fD Dark frequency
Ee = 0 μW/cm2 00.3 Hz
Ee = 0 μW/cm2, TA = 50°C (1) 06Hz
Re Irradiance responsivity 3.4 kHz/(μW/
cm2)
λp Peak response
wavelength 700 nm
Nonlinearity (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
ams Datasheet Page 7
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TSL238T − Typical Characteristics
Figure 9:
Output Frequency vs Irradiance
Figure 10:
Photodiode Spectral Responsivity
Typical Characteristics
1
0.1
0.01
0.001
0.001 0.01 0.1 1 10
10
100
IRRADIANCE
100 1 k
Ee  Irradiance PW/cm2
VDD = 5 V
Op = 640 nm
TA = 25qC
1000
Output Frequency (fO  fD) — kHz
300 400 500 600 700 1000800 900 1100
O  Wavelength  nm
Normalized Responsivity
0
0.2
0.4
0.6
0.8
1
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TSL238T − Typ ic al C ha ra cte ri st ic s
Figure 11:
Supply Current vs. Free-Air Temperature
Figure 12:
Output Frequency vs. Free-Air Temperature
TA  Free-Air Temperature  qC
fO — Output Frequency — Normalized
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
25 0 25 50 75
ams Datasheet Page 9
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TSL238T − Typical Characteristics
Figure 13:
Normalized Output Voltage vs. Angular Displacement
Figure 14:
Normalized Output Voltage vs. Angular Displacement
NORMALIZED OUTPUT VOLTAGE
vs.
ANGULAR DISPLACEMENT
Q  Angular Displacement  q
VO — Output Voltage — Normalized
0
0.2
0.4
0.6
0.8
1
90 60 30 0 30 60 90
Optical Axis
-Q +Q
NORMALIZED OUTPUT VOLTAGE
vs.
ANGULAR DISPLACEMENT
Q  Angular Displacement  q
VO — Output Voltage — Normalized
0
0.2
0.4
0.6
0.8
1
90 60 30 0 30 60 90
Optical Axis
-Q +Q
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TSL238T − Typ ic al C ha ra cte ri st ic s
Figure 15:
Dark Frequency vs.Free-Air Temperature
Note(s):
1. 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 16:
Photodiode Responsivity Temperature Coefficient Vs.
Wavelength of Incident Light
fD  Dark Frequency  Hz
TA ï Free-Air Temperature ï qC
ï7.5
ï4.5
ï1.5
1.5
4.5
7.5
ï25 ï515355575
ï6.0
ï3.0
0.0
3.0
6.0
NOTE 1
OWavelength of Incident Light  nm
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
ams Datasheet Page 11
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TSL238T − 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 TSL238T
(Figure 17). A low-noise power supply is required to minimize
jitter on output pulse.
Figure 17:
Typical TSL238T Interface to a Microcontroller
Device Operational Details
The frequency at the output pin (OUT) is given by:
where:
fO is the output frequency
fD is the output frequency for dark condition (Ee = 0)
Re is the device responsivity for a given wavelength of light
given in kHz/(μW/cm2)
Ee is 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 TSL238T 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
Application Information
TSL238T Timer / Port
MCU
0.1 PF
VDD
VDD
OUT
GND
(EQ1)
fOfDRe
()Ee
()⋅+=
Page 12 ams Datasheet
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TSL238T − Application Information
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.
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.
ams Datasheet Page 13
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TSL238T − Application Information
PCB Pad Layout
Suggested PCB pad layout guidelines for the T package are
shown in Figure 18.
Figure 18:
Suggested T Package PCB Layout
Note(s):
1. All linear dimensions are in millimeters.
2. This drawing is subject to change without notice.
1.50
2.90
0.90
1.00
Page 14 ams Datasheet
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TSL238T − Mechanical Data
The TSL238T is supplied in a low-profile surface-mount
package. This package contains no lead (Pb).
Figure 19:
Package T — Four-Lead Surface Mount Device Packaging Configuration
Note(s):
1. All linear dimensions are in millimeters.
2. Terminal finish is gold, 1.3 μm minimum.
3. The center of the 0.84-mm × 0.84-mm photodiode active area is referenced to the upper left corner of the package (near Pin 1).
4. Dimension tolerance is ± 0.15 mm.
5. This drawing is subject to change without notice.
Mechanical Data
Green
RoHS
BOTTOM VIEW
A
PIN 1
1.50
0.55
DETAIL A: TYPICAL PACKAGE TERMINAL
0.80
0.900.10
0.40
R 0.20
SIDE VIEW
1.35
3.10 7
0.35
ÈÈÈÈÈÈÈÈ
ÈÈÈÈÈÈÈÈ
ÎÎÎ
ÎÎÎ
0.50
0.45
TOP VIEW
1.89
1.0
3.80
2.60
Photodiode
(Note 3)
ams Datasheet Page 15
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TSL238T − Mechanical Data
Figure 20:
Four Lead Surface Mount Package Carrier Tape
Note(s):
1. All linear dimensions are in millimeters.
2. The dimensions on this drawing are for illustrative purposes only. Dimensions of an actual carrier may vary slightly.
3. Symbols on drawing Ao, Bo, and Ko are defined in ANSI EIA Standard 481-B 2001.
4. Each reel is 178 millimeters in diameter and contains 1000 parts.
5. ams packaging tape and reel conform to the requirements of EIA Standard 481-B.
6. In accordance with EIA standard, device pin 1 is located next to the sprocket holes in the tape.
7. This drawing is subject to change without notice.
0.30 0.050 2.10
4 0.100
2 0.100
8 Typ
1.75 0.100
5.50
0.100
AA
B
B
12 0.100
R 0.20 TYP
1.50
1.50
SIDE VIEW
TOP VIEW
END VIEW
3.09 MAX
2.90 0.100 Ao
R 0.20 TYP
1.80 Ko
4.29 MAX
4.10 0.100 Bo
DETAIL B
DETAIL A
R 0.20 TYP
Page 16 ams Datasheet
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The reflow profile specified here describes expected maximum
heat exposure of devices during the solder reflow process of
the device on a PWB. Temperature is measured at the top of the
device. Devices should be limited to one pass through the
solder reflow profile.
Figure 21:
TSL238T Solder Reflow Profile
Figure 22:
TSL238T Solder Reflow Profile
Note(s):
1. This drawing is not to scale
Parameter Reference TSL238T
Average temperature gradient in preheating 2.5°C/s
Soak time tsoak 2 to 3 minutes
Time above T1, 217°C t1 Max 60 s
Time above T2, 230°C t2 Max 50 s
Time above T3, (Tpeak −10°C) t3 Max 10 s
Peak temperature in reflow Tpeak 260°C (−0°C/ 5°C)
Temperature gradient in cooling Max −5°C/s
Manufacturing Information
t3
t2
t1
tsoak
T3
T2
T1
Tpeak
Not to scale — for reference o
Time (s)
Temperature (5C)
ams Datasheet Page 17
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TSL238T − Manufacturing Information
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 ensure the package molding
compound contains the smallest amount of absorbed moisture
possible, each device is dry-baked prior to being packed for
shipping. Devices are packed in a sealed aluminized envelope
with silica gel to protect them from ambient moisture during
shipping, handling, and storage before use.
This package has been assigned a moisture sensitivity level of
MSL 3 and the devices should be stored under the following
conditions:
•Temperature Range: 5ºC to 50ºC
•Relative Humidity: 60% maximum
•Total Time: 6 months from the date code on the
aluminized envelope — if unopened
•Opened Time: 168 hours or fewer
Rebaking will be required if the devices have been stored
unopened for more than 6 months or if the aluminized envelope
has been open for more than 168 hours. If rebaking is required,
it should be done at 90ºC for 4 hours.
Page 18 ams Datasheet
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TSL238T − Ordering & Contact Information
Figure 23:
Ordering Information
Buy our products or get free samples online at:
www.ams.com/ICdirect
Technical Support is available at:
www.ams.com/Technical-Support
Provide feedback about this document at:
www.ams.com/Document-Feedback
For further information and requests, e-mail us at:
ams_sales@ams.com
For sales offices, distributors and representatives, please visit:
www.ams.com/contact
Headquarters
ams AG
Tobelbaderstrasse 30
8141 Premstaetten
Austria, Europe
Tel: +43 (0) 3136 500 0
Website: www.ams.com
Ordering
Code Device TA Package − Leads Package
Designator
TSL238T TSL238T -40°C to 85°C 4-lead Low Profile Surface Mount T
Ordering & Contact Information
ams Datasheet Page 19
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TSL238T − RoHS Compliant & ams Green Statement
RoHS: The term RoHS compliant means that ams AG products
fully comply with current RoHS directives. Our semiconductor
products do not contain any chemicals for all 6 substance
categories, including the requirement that lead not exceed
0.1% by weight in homogeneous materials. Where designed to
be soldered at high temperatures, RoHS compliant products are
suitable for use in specified lead-free processes.
ams Green (RoHS compliant and no Sb/Br): ams Green
defines that in addition to RoHS compliance, our products are
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: The information provided in this
statement represents ams AG knowledge and belief as of the
date that it is provided. ams AG 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. ams AG 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. ams AG
and ams AG suppliers consider certain information to be
proprietary, and thus CAS numbers and other limited
information may not be available for release.
RoHS Compliant & ams Green
Statement
Page 20 ams Datasheet
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TSL238T − Copyrights & Disclaimer
Copyright ams AG, Tobelbader Strasse 30, 8141 Premstaetten,
Austria-Europe. Trademarks Registered. All rights reserved. The
material herein may not be reproduced, adapted, merged,
translated, stored, or used without the prior written consent of
the copyright owner.
Devices sold by ams AG are covered by the warranty and patent
indemnification provisions appearing in its General Terms of
Trade. ams AG makes no warranty, express, statutory, implied,
or by description regarding the information set forth herein.
ams AG reserves the right to change specifications and prices
at any time and without notice. Therefore, prior to designing
this product into a system, it is necessary to check with ams AG
for current information. This product is intended for use in
commercial applications. Applications requiring extended
temperature range, unusual environmental requirements, or
high reliability applications, such as military, medical
life-support or life-sustaining equipment are specifically not
recommended without additional processing by ams AG for
each application. This product is provided by ams AG “AS IS”
and any express or implied warranties, including, but not
limited to the implied warranties of merchantability and fitness
for a particular purpose are disclaimed.
ams AG shall not be liable to recipient or any third party for any
damages, including but not limited to personal injury, property
damage, loss of profits, loss of use, interruption of business or
indirect, special, incidental or consequential damages, of any
kind, in connection with or arising out of the furnishing,
performance or use of the technical data herein. No obligation
or liability to recipient or any third party shall arise or flow out
of ams AG rendering of technical or other services.
Copyrights & Disclaimer
ams Datasheet Page 21
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TSL238T − Document Status
Document Status Product Status Definition
Product Preview Pre-Development
Information in this datasheet is based on product ideas in
the planning phase of development. All specifications are
design goals without any warranty and are subject to
change without notice
Preliminary Datasheet Pre-Production
Information in this datasheet is based on products in the
design, validation or qualification phase of development.
The performance and parameters shown in this document
are preliminary without any warranty and are subject to
change without notice
Datasheet Production
Information in this datasheet is based on products in
ramp-up to full production or full production which
conform to specifications in accordance with the terms of
ams AG standard warranty as given in the General Terms of
Trade
Datasheet (discontinued) Discontinued
Information in this datasheet is based on products which
conform to specifications in accordance with the terms of
ams AG standard warranty as given in the General Terms of
Trade, but these products have been superseded and
should not be used for new designs
Document Status
Page 22 ams Datasheet
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TSL238T − Revision Information
Note(s):
1. Page and figure numbers for the previous version may differ from page and figure numbers in the current revision
2. Correction of typographical errors is not explicitly mentioned.
Changes from 080G (Dec-2007) to current revision 1-00 (2016-May-25) Page
Content of TAOS datasheet was updated to latest ams design
Updated Key Benefits & Features 1
Revision Information
ams Datasheet Page 23
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TSL238T − Content Guide
1 General Description
1 Key Benefits & Features
2 Functional Block Diagram
3 Pin Assignments
4Absolute Maximum Ratings
5 Electrical Characteristics
7 Typical Characteristics
11 Application Information
11 Power-Supply Considerations
11 Device Operational Details
12 Output Interface
12 Measuring the Frequency
13 PCB Pad Layout
14 Mechanical Data
16 Manufacturing Information
17 Moisture Sensitivity
18 Ordering & Contact Information
19 RoHS Compliant & ams Green Statement
20 Copyrights & Disclaimer
21 Document Status
22 Revision Information
Content Guide