sp4403 Exar Corporation, sp4403 Datasheet - Page 6

• Manufacturer Part Number: sp4403
• Description: Low Voltage Electroluminescent Lamp Driver
• Manufacturer: Exar Corporation

The Switched H-Bridge Network
The H-bridge consists of two SCR structures
that act as high voltage switches. These two
switches control the polarity of how the lamp is
charged. The SCR switches are controlled by
the f
divided by 128. For a 50kHz oscillator, the 7 flip
flops will drive f
When the energy from the coil is released, a high
voltage spike is created triggering the SCR
switches. The direction of current flow is
determined by which SCR is enabled. One full
cycle of the H-bridge will create 128 voltage
steps from ground to 80V (typical) on EL1 and
EL2 (pins 4 and 5, respectively) which are 180
degrees out of phase from each other (see
Figure 5). A differential representation of the
output is shown in Figure 6.
Fine Tuning Performance
Circuit performance of the SP4403 can be
improved with some of the following
suggestions:
Increase EL Lamp Light Output: By
connecting a fast recovery diode from COIL
(pin 3) to C
switched H-bridge network is bypassed resulting
in an increase in light output at the EL lamp.
We suggest a fast recovery diode, such as the
industry standard 1N4148, be used for D1. This
circuit connection can be found in Figure 2.
Square Wave Output Waveform to the EL
Lamp: A 470pF capacitor at C
act as an integrating capacitor, filtering out any
coil switching spikes or ripple in the output
waveform to the EL lamp (shown if Figure 1).
SP4403DS/05
LAMP
signal which is the oscillator frequency
INT
(pin 7), the internal diode of the
LAMP
= 390Hz.
INT
(pin13) will
SP4403 Electroluminescent Lamp Driver
6
A designer may change the output waveform to
a square wave by using a 0.1 F capacitor (shown
in Figure 2) at C
Printed Circuit Board Layout Suggestions:
The SP4403's high-frequency operation makes
PC layout important for minimizing ground
bounce and noise. Keep the IC's GND pin and
the ground leads of C1 and C
than 0.2in (5mm) apart. Also keep the
connections to L1 (pin 3) as short as possible.
To maximize output power and efficiency and
minimize output ripple voltage, use a ground
plane and solder the IC's V
the ground plane.
EL Lamp Driver Design Challenges
There are many variables which can be optimized
for specific applications. The amount of light
emitted is a function of the voltage applied to the
lamp, the frequency at which it is applied, the
lamp material, the lamp size, and the inductor
used. Sipex supplies characterization charts to
aid the designer in selecting the optimum circuit
configuration (see Figures 7 to 14).
Sipex will perform customer application
evaluations, using the customer's actual EL
lamp to determine the optimum operating
conditions for specific applications. For
customers considering an EL backlighting
solution for the first time, Sipex is able to offer
retrofitted solutions to the customer's existing
LED or non-backlit product for a thorough
electrical and cosmetic evaluation. Please
contact your local Sales Representative for Sipex
or the Sipex factory directly to initiate this
valued service.
INT
(pin 13).
© Copyright 2000 Sipex Corporation
SS
INT
(pin 2) directly to
in Figure 2 less