Micrel
MIC4832
Application Information
Inductor
A 220µH Murata (LQH4C221K04) inductor is
recommended for most applications. Generally,
inductors with smaller values can handle more
current. Lowering the inductance allows the boost
regulator to draw more input current to deliver more
energy every cycle. As a result, a lower value
inductor may be used to drive larger panels or make
the current panel brighter. However, caution is
required as using a low value inductor with a low
switching frequency may result in voltages
exceeding the absolute maximum rating of the
switch node and/or the CS pin. If the application
uses a low input voltage (1.8 to 3V), a lower value
inductor, such as 100µH, may be used in order to
drive the EL lamp at max brightness without issue.
Diode
An ideal diode to use would be the 1N4148 or
equivalent. It has a forward current of 150mA and a
typical forward voltage of 950mV. For applications
that are not cost driven, a fast switching diode with
lower forward voltage and higher reverse voltage
can be used to enhance the efficiency, such as
BAV20WS or BAS20W.
Output Capacitor
Low ESR capacitors should be used at the regulated
boost output (CS pin) of the MIC4832 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 MIC4832 circuit. Selection of the
capacitor value will depend upon the peak inductor
current, inductor size, and the load. The MIC4832 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 at
200V to 250V rating in 0805 size. If output ripple is a
concern a 0.01µF/200V X7R output capacitor is
recommended.
EL Lamp Terminals (VA, VB)
An EL lamp is connected from VA to VB as the load.
The high voltage alternated across VA and VB by
the H-Bridge cycles generate luminance. The
voltage at VA and VB should not exceed the voltage
at V
CS
by more than 3V. This situation may become
present when noisy enable signals such as those
often generated by mechanical switches are applied
to the driver’s inputs. To prevent over voltage at VA
and VB, 10kΩ resistors may be placed in series from
VA to the EL panel and from VB to the EL panel. An
alternative to the use of 10kΩ resistors is to apply a
diode from the CS pin to VA and VB, where the
cathode of the diode is on the CS side and the
anode is on the VA and VB side, respectively.
November 2007
7
M9999-111507-B
MICREL [ MICREL SEMICONDUCTOR ]
