ISL29000 Ver la hoja de datos (PDF) - Renesas Electronics
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ISL29000 Datasheet PDF : 7 Pages
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ISL29000
Pin Descriptions
PIN
NAME
DESCRIPTION
1
VCC Supply, 2.5V to 5.5V
2
GND Ground
3
EN
Enable
4
NC
No connect
5
Output Current output pin
Block Diagram
VCC
1
3
ENABLE
5
OUTPUT
2
GND
Application Information
Product Description
The ISL29000 is a light-to-current optical sensor combining
photodiodes and current amplifiers on a single monolithic IC.
The photodiodes are temperature-compensated and their
spectrum resembles the human eye response. The output
current is directly proportional to the intensity of light falling on
the photodiodes. For 100 lux of input fluorescent light, the
ISL29000 has an output current of 6.5µA.
The ISL29000 is housed in an ultra-compact surface mount
clear plastic package.
Light-to-Current and Voltage Conversion
The ISL29000 has a responsiveness that is directly
proportional to the intensity of light intercepted by the
photodiodes. Although the conversion rate varies depending
on the light sources (fluorescent light, incandescent light or
direct sunlight), in general for a fluorescent light, the
light-to-current conversion is:
IOUT
=
1----0-6--0--1-0----L--A--u----x-
LINPUT
(EQ. 1)
Here, IOUT is the output current in µA, and LINPUT is the input
light in lux.
For some applications, a load resistor is added between the
output and the ground as shown in Figure 1. The output
voltage can be expressed in Equation 2:
VOUT = IOUT RLOAD = 1----0-6--0--1-0----L--A--u----x- LINPUT RLOAD
(EQ. 2)
Here, VOUT is the output voltage and RLOAD is the value of the
load resistor added. The compliance of the ISL29000's output
circuit may result in premature saturation of the output current
and voltage when an excessively large RLOAD is used. The
output compliance voltage is 300mV below the supply voltage
as listed in VO(MAX) of “Electrical Specifications” on page 2.
In order to have the linear relationship between the input light
and the output current and voltage, a proper resistor value (i.e.,
gain) should be picked for a specific input light range. The
resistor value can be picked according to Equation page 4:
RLOAD = ---V----S----U--6--·P-1----–----A-0---.--3----V---- -1L---0R---0-A---0-N--L---G-u---E-x-
(EQ. 3)
Here, VSUP is the supply voltage, and LRANGE is the specific
input light range for an application. For example, an indoor light
ranges typically from 0 lux to 1,000 lux. A resistor value of
45k for 3V supply voltage can be used. For a small light
range, a large resistor value should be used to achieve better
sensitivity; for a large light range, a small resistor value should
be used to prevent non-linear output current and voltage.
Resistor Output RLOAD Selection
The resistor output, RLOAD, determines the voltage transfer
function of the device. The device converts light into current
then RLOAD converts the output current to an output voltage.
RLOAD can range from 10 to 10M depending on the input
lux levels. The table below lists RLOAD values to maximize
output swing for typical lux range levels. A careful balance of
dynamic swing and fast response has to be considered when
choosing RLOAD. For faster response, choose a smaller value
RLOAD to shunt stray capacitances that may slow down
response time. For maximum dynamic range or swing, choose
a higher value RLOAD. Although finite, the output impedance of
the device is considerably large. Hence, the light-to-current
conversion deviation because of resistor loading is
infinitesimal. The recommended maximum RLOAD is 10M.
Although the device saturates at 10,000 lux (IOUT = 600µA),
the output current must never exceed 6mA. The voltage output
compliance of the device is 300mV below the supply. The
output current stops ramping when the output voltage reaches
voltage compliance.
TABLE 1. VDD = 5V, MAXIMUM OUTPUT VOLTAGE = 4.7V
ILLUMINATION RANGE
(LUX)
RLOAD
(k)
CURRENT OUT
(µA)
0 to 10
7830
0 to 0.6
FN6117 Rev 6.00
September 2, 2008
Page 4 of 7
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