el7900

EL7900

Ambient Light Photo Detect IC

The EL7900 is a light-to-current optical sensor combining a photodiode and a current amplifier on a single monolithic IC. Output current is directly proportionate to the light intensity on the photodiode. Its sensitivity is superior to that of a phototransistor and exhibits little variation. Its spectral sensitivity matches closely to the luminous efficiency and linearity.

Housed in an ultra-compact surface mount clear plastic package, this device is excellent for power saving control function in cell phones, PDAs, and other handheld applications.

Pinout

EL7900(5 LD DFN)TOP VIEW

Features

•Monolithic IC containing photodiode and amplifier • 1 Lux to 10,000 Lux range •Converts light intensity to current • 2.5V to 5.5V supply range •Low supply current - 1µA •Fast response time - <200µs

•Excellent output linearity of luminance

•Ultra-compact and light surface mount package •Pb-free plus anneal available (RoHS compliant)

Applications

•Mobile phones •Notebook PCs •PDAs

•Video cameras •

Digital cameras

Ordering Information

PART NUMBER TAPE & REEL

PACKAGE

PKG. DWG. #

EL7900ILCZ (Note)- 5 Ld ODFN (Pb-free)MDP0052EL7900ILCZ-13 (Note)

13”

5 Ld ODFN (Pb-free)MDP0052

NOTE:Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.

FIGURE 1.RISE/FALL TIME MEASUREMENT FIGURE 2.

Absolute Maximum Ratings (T A = 25°C)

Supply Voltage between V SD and GND . . . . . . . . . . . . . . . . . . . .6V Maximum Continuous Output Current. . . . . . . . . . . . . . . . . . . . 6mA Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40°C to +85°C ESD Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2kV

Maximum Die Temperature . . . . . . . . . . . . . . . . . . . . . . . . . .+125°C Storage Temperature. . . . . . . . . . . . . . . . . . . . . . . .-45°C to +100°C

CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.

IMPORTANT NOTE:All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: T J = T C = T A

Electrical Specifications

V CC = 3V , T A = 25°C, fluorescent light, unless otherwise specified.

PARAMETER DESCRIPTION

CONDITION

MIN

TYP MAX

UNIT I CC1

Supply Current

R L = 1k Ω, EV = 100lx 62µA EV = 0lx

1µA I CC2Supply Current When Disabled EN = V HI 1.2

µA I L1Light Current EV = 100lx 39

60.582µA I L2Light Current EV = 10lx 6.2µA I LEAK Dark Current

EV = 0lx

0.15µA V O-MAX Maximum Output Compliance Voltage at 95% of nominal output current, EV = 100lx 2.7V T R

Rise Time (See Note)

R L = 5k Ω, EV = 300lx 105125µs R L = 1k Ω, EV = 1000lx

µs T F

Fall Time (See Note)

R L = 5k Ω, EV = 300lx 170225µs R L = 1k Ω, EV = 1000lx

77µs T D

Delay Time for Rising Edge (See Note)

R L = 5k Ω, EV = 300lx 165200µs R L = 1k Ω, EV = 1000lx

112µs T S

Delay Time for Falling Edge (See Note)

R L = 5k Ω, EV = 300lx 6585µs R L = 1k Ω, EV = 1000lx

33

µs V LO Maximum Voltage at EN Pin to Enable 0.6

V V HI Minimum Voltage at EN Pin to Disable 1.8

V I LO Input Current at EN Pin V EN = 0V 0.01µA I HI Input Current at EN Pin V EN = 3V 2µA T EN Enable Time EV = 200lx 140µs T DIS

Disable Time

EV = 200lx

2

µs

NOTE:Switching time measurement is based on Figures 1 and 2.

EL7900

PULSE DRIVE

V CC

R L

V OUT

CH1

CH2

PULSE DRIVE

V OUT

T D T R

80%20%T S

T F

1mS 1V

0.5V

V S =3V T A =27°C

Typical Performance Curves

FIGURE 3.RELATIVE SENSITIVITY FIGURE 4. SENSITIVITY

FIGURE 5.DARK CURRENT vs TEMPERATURE FIGURE 6. GAIN vs TEMPERATURE

FIGURE 7.OUTPUT COMPLIANCE VOLTAGE vs CURRENT

FIGURE 8. RADIATION PATTERN

SPECTRAL WAVELENGTH (nm)

R E L A T I V E S E N S I T I V I T Y (%)

4284444604792508524540556572588604620636652668

10075

50

25

ILLUMINATION (L X )

O U T P U T C U R R E N T (µA )

700

6004002000500300100

200

400

600

800

1000

V CC = 3V

FLUORESCENT LIGHT

TEMPERATURE (°C)O U T P U T C U R R E N T - N O L I G H T (µA )

0.2

0.18

0.14

0.10.16

0.12

-60

-4004080100

-202060V DD =3V

TEMPERATURE (°C)

G A I N /G A I N (25°C )

1.2

1.150.950.81.050.85

-60

-4004080100

-2020601.10.91V DD =3V

FLUORESCENT LIGHT OF 50 LUX OUTPUT CURRENT (µA)

O U T P U T C O M P L I A N C E V O L T A G E (V D D -V O U T ) (V )

0.6

0.50.200.30.1

-200

040080010001200

200600V DD =3V T A =27°C

0.4

Block Diagram

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.

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:

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:

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 Vo-max of Electrical Specifications.

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:

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 0 to 1,000Lux. A resistor value of 4.5k Ω 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.

Application Examples

The following examples present from fully automatic to fully manual override implementations. These guidelines are applicable to a wide variety of potential light control applications. The EL7900 can be used to control the

brightness input of CCFL inverters. Likewise it can interface well with LED drivers. In each specific application, it is important to recognize the target environment and its ambient light conditions. The mechanical mounting of the sensor, light aperture hole size and use of a light pipe or bezel are critical in determining the response of the EL7900 for a given exposure of light.

The example in Figure 9 shows a fully automatic dimming solution with no user interaction. Choose R 1 and R 2 values for any desired minimum brightness and slope. Choose C 1 to adjust response time and to filter 50/60Hz room lighting. For example, suppose you wish to generate an output voltage from 0.25V to 1.25V to drive the input of an LED driver controller. The 0.25V represents the minimum LED brightness and 1.25V represents the maximum. The 1st step would be to determine the ratio of R 1 and R 2:

Pin Descriptions

PIN NAME DESCRIPTION

1VCC Supply, 2.5V to 5.5V 2GND Ground 3EN Enable 4NC No connect 5

Output

Current output pin

ENABLE

OUTPUT

GND

VCC 1

25

3

I OUT 60µA

100Lux --------------------

L INPUT

×=V OUT I OUT R LOAD ×60µA

100Lux --------------------

L INPUT R LOAD

××==R LOAD V SUP 0.3V –()60µA --------------------------------------100Lux

L RANGE

-----------------------×=R 1R 2 3.0V

0.25V ---------------1–

×11R 2

×==

Next the value of R 2 can be calculated based on the

maximum output current coming from the EL7900 under the application's maximum light exposure. Suppose the current has been determined to be about 125µA. Thus R 2 can be calculated approximately as follows:

and

In Figure 10, user adjustable bias control has been added to allow control over the minimum and maximum output

voltage. This allows the user to adjust the output brightness to personal preference over a limit range.

Figure 11 shows how a fully manual override can be quickly added by using the EN pin.

Short Circuit Current Limit

The EL7900 does not limit the output short circuit current. If the output is directly shorted to the ground continuously, the output current could easily increase for a strong input light such that the device may be damaged. Maximum reliability is maintained if the output continuous current never exceeds 6mA by adding a load resistor at the output. This limit is set by the design of the internal metal interconnects.

Suggested PCB Footprint

Footprint pads should be a nominal 1-to-1 correspondence with package pads. The large, exposed central die-mounting paddle in the center of the package requires neither thermal nor electrical connections to PCB, and such connections should be avoided.

Power Supply Bypassing and Printed Circuit Board Layout

The EL7900 is relatively insensitive to the printed circuit board layout due to its low speed operation. Nevertheless, good printed circuit board layout is necessary for optimum performance. Ground plane construction is highly

recommended, lead length should be as short as possible and the power supply pins must be well bypassed to reduce the risk of oscillation. For normal single supply operation, where the GND pin is connected to ground, a 0.1µF ceramic capacitor should be placed from V CC pin to GND pin. A 4.7µF tantalum capacitor should then be connected in parallel, placed close to the device.

3V TO 5V

SUPPLY VOLTAGE

3V DC VOLTAGE

EL7900

OUT

EN

GND

VDO

To Inverter Brightness Input or LED Driver Controller C1R1R2FIGURE 9.

10k

25µF

110k

R 2 1.25V

125µA -----------------

10k Ω

==R 111R 2×110k Ω

==3V TO 5V

SUPPLY VOLTAGE

3V PWM CONTROL

EL7900

OUT

EN

GND

VDO

To Inverter Brightness Input or LED Driver Controller FIGURE 10.

C1R1R210k

25µF

110k

3V TO 5V

SUPPLY VOLTAGE

3V PWM CONTROL

EL7900

OUT

EN

GND

VDO

To Inverter

or LED Driver FIGURE 11.

Brightness Input Controller ENABLE/CONTROL

DISABLE C1R1R210k

25µF

110k

NOTE:The package drawing shown here may not be the latest version. To check the latest revision, please refer to the Intersil website at

http://www.intersil.com/design/packages/index.asp

All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.

Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality

Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.

For information regarding Intersil Corporation and its products, see www.intersil.com