MIC4833 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Low Noise Dual 220 VPP EL Driver With Output Voltage Slew Rate Control

Micrel
MIC4833
Application Information
The MIC4833 is designed to use an inductance with
a value between 100µH to 330µH. Choosing the
right inductor is always a balance of size,
inductance, efficiency, current rating and cost. A
TDK (VLS4012T-221M) 220µH inductor is
recommended based on size, efficiency and current
rating.
Generally, the lower the inductance, the more
current the inductor can handle. Lowering the
inductance allows the boost regulator to draw more
input current to deliver more energy every switching
cycle. As a result, a lower inductance may be used
to drive larger panels or brighten similar sized
panels. However, caution is required as using a low
inductance with a low switching frequency may
cause the voltage at the switch node and the CS pin
to exceed the absolute maximum rating. If the
application uses a low input voltage (2.3 to 3V), a
lower value inductor, such as 100µH, may be used
in order to drive the EL panel at maximum
brightness.
Diode
The diode must have a high reverse voltage (150V),
since the output voltage at the CS pin can reach up
to 130V. A fast switching diode with lower forward
voltage and higher reverse voltage (150V), such as
BAV20WS/BAS20W, can be used to enhance
efficiency.
Output Capacitor
Low ESR capacitors should be used at the regulated
boost output (CS pin), to minimize the switching
output ripple voltage. The larger the output
capacitance, the lower the output ripple at the CS
pin. The reduced output ripple at the CS pin along
with a low ESR capacitor improves the efficiency of
the MIC4833 circuit. Selection of the capacitor value
depends upon the peak inductor current, inductor
size, and the load. The MIC4833 is designed for use
with an output capacitance as low as 2.2nF. For
minimum audible noise, the use of a C0G/NPO
dielectric output capacitor is recommended. TDK
and AVX offer C0G/NPO dielectric capacitors in
capacitances up to 2.7nF capacitance at 200V to
250V voltage rating in 0805 size.
EL Panel Terminals (ELA, ELB, COM)
The two EL panels are connected from ELA to COM
and ELB to COM. The ELA and ELB terminals are in
phase with each other, while the COM is out of
phase with both ELA and ELB. Since ELA and COM
are out of phase, the high voltage generated by the
boost regulator is alternated across ELA and COM
by the H-Bridge. The frequency of each cycle is
determined by R_EL. The alternating 220V peak-to-
peak causes the EL panel to emit light. Similarly, the
ELB and COM are also out of phase and allows a
second EL panel to be driven at the same time. Both
EL panels may operate independently from each
other and do not have to be the same size. For
component selection, Table 2 lists recommended
values for various panel sizes up to a total of 8in²
(For example, two 4in² panels). Driving overly large
panels will result in a dimmer display, but will not
cause damage to the device.
October 2008
8
M9999-100308
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