EL7900
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.
3V TO 5V
SUPPLY VOLTAGE
3V PWM CONTROL
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.
VDO
R
2
110k
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.
EL7900
EN
OUT
R
1
10k
TO INVERTER BRIGHTNESS
INPUT OR LED DRIVER
CONTROLLER
C
1
25µF
GND
Power Supply Bypassing and Printed Circuit
Board Layout
FIGURE 11. AUTOMATIC DIMMING SOLUTION WITH
ADJUSTABLE BIAS CONTROL
Figure 12 shows how a fully manual override can be quickly
added by using the EN pin.
3V TO 5V
SUPPLY VOLTAGE
3V PWM CONTROL
VDO
R
2
110k
ENABLE/
DISABLE
CONTROL
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.
EL7900
EN
OUT
R
1
10k
TO INVERTER
BRIGHTNESS
INPUT OR
CONTROLLER
C
1
25µF
GND
LED DRIVER
FIGURE 12. AUTOMATIC DIMMING SOLUTION WITH
ADJUSTABLE BIAS CONTROL AND MANUAL
OVERRIDE
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
6
FN7377.5
February 6, 2007
INTERSIL [ INTERSIL CORPORATION ]
