mic4834 Micrel Semiconductor, mic4834 Datasheet - Page 6

• Manufacturer Part Number: mic4834
• Description: Low Noise Dual 220 Vpp El Driver
• Manufacturer: Micrel Semiconductor

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
energy in the inductor is then discharged into the C
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 disables switching. The control
circuit will continue to turn the MOSFET’s on and off to
maintain a constant DC voltage at the CS pin.
When the MIC4834 EL Driver is enabled, ELA and ELB
will switch in opposite states with COM to achieve a
220V peak-to-peak AC output signal needed to drive the
two EL panels.
Switching Frequency
The switching frequency of the converter is controlled by
an external resistor (R
switching frequency increases as the resistor value
decreases.
frequency, the greater the input current is drawn to
deliver more power to the output. Lowering the switching
frequency can be used to drive larger panels. However,
the switching frequency should not be so low as to allow
the voltage at the switch node or the CS pin to exceed
the absolute maximum voltage of those pins. For resistor
value selections, see the “Typical Characteristics:
Switching Frequency vs. SW Resistor” graph on Page 4
or use the equation below. The switching frequency
range is 35kHz to 350kHz, with an accuracy of ±20%.
EL Frequency
The MIC4834 EL panel frequency is internally fixed at
225Hz.
Enable Function
There are a few different ways to enable and disable the
MIC4834. The boost regulator may be disabled by
pulling the R
EL panels by cutting power to the device completely.
The R
boost oscillator. If it is not equal to VDD, then the
frequency set by R
value.
For individual panel control, the ENA and ENB pins can
be used to enable ELA and ELB, respectively. Pulling
Micrel
October 2008
SW
f
SW
resistor must be pulled to VDD to enable the
(kHz)
SW
In
resistor to ground. This turns off both the
general,
=
SW
R
SW
SW
will be different the programmed
46
) between RSW and VDD. The
(
M
Ω
the
)
lower
OUT
the
+ V
switching
D1
. The
OUT
6
ENA or ENB high (over 1.2V) or low (below 0.4V) will
turn ELA and ELB panels on or off.
Figure 2. EL Panel Waveform – 2 × 1 in
Figure 3. EL Panel Waveform – 2 × 2 in
Figure 4. EL Panel Waveform – 2 × 3 in
M9999-100908-A
MIC4834
2
2
2