Micrel
MIC4832
Functional Diagram
Figure 1. MIC4832 Block Diagram
Functional Description
Overview
The MIC4832 is a high-voltage EL driver with an AC
output voltage of 220V peak-to-peak capable of
driving EL lamps up to 3 in
2
. Input supply current for
the MIC4832 is typically 45µA reducing to 10nA in
shutdown. The high voltage EL driver has two
internal oscillators to control the switching MOSFET
and the H-bridge driver. Both of the internal
oscillators’ frequencies can be individually
programmed through the external resistors to
maximize the efficiency and the brightness of the EL
lamp.
Regulation
Referring to Figure 1, initially power is applied to
V
DD
. The internal feedback voltage is less than the
reference voltage causing the internal comparator to
go high which enables the switching MOSFET’s
oscillator. When the switching MOSFET turns on,
current flows through the inductor and flows into the
switch. The switching MOSFET will typically turn on
for 90% of the switching period. During the on-time,
energy is stored in the inductor. When the switching
MOSFET turns off, current flowing into the inductor
forces the voltage across the inductor to reverse
polarity. The voltage across the inductor rises until
the external diode conducts and clamps the voltage
at V
OUT
+ V
D1
. The energy in the inductor is then
discharged into the C
OUT
capacitor. The internal
comparator continues to turn the switching MOSFET
on and off until the internal feedback voltage is
above the reference voltage. Once the internal
feedback voltage is above the reference voltage, the
internal comparator turns off the switching
MOSFET’s oscillator.
When the EL oscillator is enabled, V
A
and V
B
switch
in opposite states to achieve a 220V peak-to-peak
AC output signal. The external resistor that connects
to the REL pin determines the EL frequency.
March 2009
5
M9999-033109-C
MICREL [ MICREL SEMICONDUCTOR ]
