ISL29000_07 Datasheet, PDF (4/7 Pages) Intersil Corporation – Ambient Light Photo Detect IC

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 100lux 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:
I_OUT = _{⎝⎛1}----₀-⁶--₀--¹-₀--^μ--_L--^A--_u----_x-_⎠⎞ × L_INPUT
(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:
V_OUT
=
I_OUT × R_LOAD
=
⎛
⎝
1^----0^-6--0^--1-0^--μ--L^--A--u^----x^{-⎠⎞}
× L_INPUT × R_LOAD
(EQ. 2)
Here, V_OUT is the output voltage and R_LOAD 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
R_LOAD is used. The output compliance voltage is 300mV
below the supply voltage as listed in V_O(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 the
following equation:
R_LOAD
=
(_---V_{----S----U--6--P·-1----μ}–----_A-0_---._--3_----V_----)
×
-¹---⁰---⁰----⁰---^L----^u----^x-
L_RANGE
(EQ. 3)
Here, V_SUP is the supply voltage, and L_RANGE is the
specific input light range for an application. For example, an
indoor light ranges typically from 0lux to 1,000lux. A resistor
value of 45kΩ 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 R_LOAD Selection
The resistor output, R_LOAD, determines the voltage transfer
function of the device. The device converts light into current
then R_LOAD converts the output current to an output voltage.
R_LOAD can range from 10Ω to 10MΩ depending on the input
lux levels. The table below lists R_LOAD 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 R_LOAD. For faster response, choose a
smaller value R_LOAD to shunt stray capacitances that may
slow down response time. For maximum dynamic range or
swing, choose a higher value R_LOAD. 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
R_LOAD is 10MΩ.
Although the device saturates at 10,000lux (I_OUT = 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.
4
FN6117.4
February 9, 2007