MIC4834 Datasheet, PDF (6/12 Pages) Micrel Semiconductor – Low Noise Dual 220 VPP EL Driver

Micrel
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 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_SW) between RSW and VDD. The
switching frequency increases as the resistor value
decreases. In general, the lower the switching
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%.
f_SW
(kHz)
=
46
R_SW (MΩ)
EL Frequency
The MIC4834 EL panel frequency is internally fixed at
225Hz.
MIC4834
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 in²
Figure 3. EL Panel Waveform – 2 × 2 in²
Enable Function
There are a few different ways to enable and disable the
MIC4834. The boost regulator may be disabled by
pulling the R_SW resistor to ground. This turns off both the
EL panels by cutting power to the device completely.
The R_SW resistor must be pulled to VDD to enable the
boost oscillator. If it is not equal to VDD, then the
frequency set by R_SW will be different the programmed
value.
For individual panel control, the ENA and ENB pins can
be used to enable ELA and ELB, respectively. Pulling
Figure 4. EL Panel Waveform – 2 × 3 in²
October 2008
6
M9999-100908-A