MIC4833 Datasheet, PDF (7/12 Pages) Micrel Semiconductor – Low Noise Dual 220 VPP EL Driver With Output Voltage Slew Rate Control

Micrel
Figure 2. 150Hz Output Waveform
Figure 3. 250Hz Output Waveform
Figure 4. 350Hz Output Waveform
October 2008
MIC4833
PWM Dimming
The MIC4833 may be dimmed by adding a shunt
capacitor (C_PWM) to the REL pin, shown in Figure 5.
The duty cycle of the PWM signal changes the
frequency of the EL panel, thereby changing its
brightness. Increasing the PWM duty cycle
increases the EL frequency to a maximum set by
R_EL (Duty Cycle = 100%). Decreasing the PWM duty
cycle decreases the EL frequency. The PWM duty
cycle should not be lowered to a level that may
cause the EL frequency to be lower than 100Hz,
since EL frequencies lower than 100Hz may cause
the panel to flicker. The frequency of the PWM
signal can range from 500Hz to 50kHz. The peak
voltage of the PWM signal should be equal to VDD.
VDD
0V
PWM
1kHz
R_EL
C_PWM
0.01µF
REL pin
Figure 5. PWM Dimming Circuit
Slew Resistor
The MIC4833 is designed to reduce audible noise in
EL panels by the use of the internal wave-shaping
circuit. To further reduce audible noise, a Slew
Resistor (R_SLEW) can be added to limit the rate of
change of the EL driver output voltage by limiting the
output current. A slower rate of change in voltage
across the EL panel creates less physical distortion
in the material and therefore reduces the amount of
audible noise. The lower the I_SLEW, the slower the
output voltage across the EL panel will change. If
R_SLEW is not used, the I_SLEW is by default 5mA,
equivalent to using a 22kΩ for R_SLEW.
R_SLEW I_SLEW
Open 5mA
125kΩ 1mA
22kΩ 5mA
10kΩ 10mA
Table 1. Slew Resistor Setting
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M9999-100308
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