EL7900
Typical Performance Curves
5
4
3
2
1
0
FLUORESCENT
LIGHT SOURCE
I
OUT
(mA)
0
1k
2k
3k 4k 5k 6k 7k
LUMINANCE (lux)
8k
9k
10k
FIGURE 9. I
OUT
vs LUMINANCE
Pin Descriptions
PIN
1
2
3
4
5
NAME
VCC
GND
EN
NC
Output
DESCRIPTION
Supply, 2.5V to 5.5V
Ground
Enable
No connect
Current output pin
Application Information
Product Description
The EL7900 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 100lux of input fluorescent light, the
EL7900 has an output current of 60µA.
The EL7900 is housed in an ultra-compact surface mount
clear plastic package.
Block Diagram
VCC
1
Light-to-Current and Voltage Conversion
The EL7900 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:
5
OUTPUT
3
ENABLE
60μA
-
I
OUT
=
⎛
------------------
⎞ ×
L
INPUT
⎝
100lux
⎠
(EQ. 1)
Here, I
OUT
is the output current in µA, and L
INPUT
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 the following equation:
60μA
-
V
OUT
=
I
OUT
×
R
LOAD
=
⎛
------------------
⎞ ×
L
INPUT
×
R
LOAD
⎝
100lux
⎠
2
GND
(EQ. 2)
Here, V
OUT
is the output voltage and R
LOAD
is the value of
the load resistor added. The compliance of the EL7900's
output circuit may result in premature saturation of the
output current and voltage when an excessively large
R
LOAD
is used. The output compliance voltage is 300mV
below the supply voltage as listed in V
O(MAX)
of the
Electrical Specifications table on page 2.
4
FN7377.5
February 6, 2007
INTERSIL [ INTERSIL CORPORATION ]
