EL7900ILCZ-EVALZ Intersil, EL7900ILCZ-EVALZ Datasheet - Page 6

• Manufacturer Part Number: EL7900ILCZ-EVALZ
• Description: BOARD EVALUATION FOR EL7900ILCZ
• Manufacturer: Intersil

Specifications of EL7900ILCZ-EVALZ

• Sensor Type: Light, Current Output
• Sensing Range: 8000Lux
• Interface: Analog
• Voltage - Supply: 2.7 V ~ 5.5 V
• Embedded: No
• Utilized Ic / Part: EL7900
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Sensitivity: -

brightness and 1.25V represents the maximum. The first
step would be to determine the ratio of R
Next, the value of R
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
calculated as shown in Equations 5 and 6:
and
In Figure 11, 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 via the 3V PWM
control.
R
R
R
1
2
1
FIGURE 11. AUTOMATIC DIMMING SOLUTION WITH
=
=
=
SUPPLY VOLTAGE
SUPPLY VOLTAGE
R
⎛
⎝
11
EN
EN
----------------- -
125μA
1.25V
2
FIGURE 10. AUTOMATIC DIMMING SOLUTION
×
×
3V TO 5V
3V TO 5V
EL7900
EL7900
R
⎛
⎝
--------------- - 1
0.25V
GND
GND
VDO
2
VDO
3.0V
⎞
⎠
=
ADJUSTABLE BIAS CONTROL
=
110kΩ
10kΩ
–
OUT
OUT
⎞
⎠
2
can be calculated based on the
=
11 R
3V DC VOLTAGE
3V PWM CONTROL
×
R
10k
R
10k
2
2
2
6
R
110k
R
110k
1
1
C
25µF
C
25µF
TO INVERTER BRIGHTNESS
INPUT OR LED DRIVER
CONTROLLER
1
INPUT OR LED DRIVER
TO INVERTER BRIGHTNESS
CONTROLLER
1
1
and R
2
:
2
can be
(EQ. 4)
(EQ. 5)
(EQ. 6)
EL7900
Figure 12 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 VCC pin to GND pin. A
4.7µF tantalum capacitor should then be connected in
parallel, placed close to the device.
CONTROL
FIGURE 12. AUTOMATIC DIMMING SOLUTION WITH
ENABLE/
DISABLE
ADJUSTABLE BIAS CONTROL AND MANUAL
OVERRIDE
SUPPLY VOLTAGE
EN
3V TO 5V
EL7900
VDO
GND
OUT
LED DRIVER
3V PWM CONTROL
R
10k
2
R
110k
1
C
25µF
1
TO INVERTER
BRIGHTNESS
INPUT OR
CONTROLLER
September 18, 2009
FN7377.8