MIC4832 Datasheet, PDF (6/11 Pages) Micrel Semiconductor – Low Noise 220Vp-p EL Driver

Micrel
V_IN = 3.6V
I_IN = 17mA
L = 220µH
C_OUT = 2.7nF
LAMP = 2 in²
R_SW = 300k
R_EL = 2.82M
MIC4832
V_IN = 3.6V
I_IN = 27mA
L = 220µH
C_OUT = 2.7nF
LAMP = 2 in²
R_SW = 332k
R_EL = 1.78M
Time (2ms/div)
Figure 2. 100Hz Output Waveform
Switching Frequency
The switching frequency of the converter is
controlled via an external resistor between R_SW pin
and V_DD pin of the device. The switching frequency
increases as the resistor value decreases. For
resistor value selections, see the “Typical
Characteristics: Switching Frequency vs. SW
Resistor” or use the equation below. The switching
frequency range is 65kHz to 250kHz, with an
accuracy of ±20%. In general, the lower the
switching frequency, the greater the input current is
drawn to deliver more power to the output.
However, the switching frequency should not be so
low as to allow the voltage at the switch node or the
CS pin to go beyond the absolute maximum voltage
of those pins.
f_SW
(kHz)
=
36
R_SW (MΩ)
EL Frequency
The EL lamp frequency is controlled via an external
resistor connected between R_EL pin and V_DD pin of
the device. The lamp frequency increases as the
resistor value decreases. For resistor value
selections, see the “Typical Characteristics: EL
Frequency vs. EL Resistor” graph on page 4 or use
the equation below. The EL lamp frequency range is
60Hz to 1000Hz, with an accuracy of ±20%.
f_EL (Hz)
=
360
R_EL (MΩ)
Time (2ms/div)
Figure 3. 200Hz Output Waveform
In general, as the EL lamp frequency increases, the
amount of current drawn from the battery will
increase. The color of the EL lamp and the intensity
are dependent upon its frequency.
V_IN = 3.6V
I_IN = 21mA
L = 220µH
C_OUT = 2.7nF
LAMP = 1 in²
R_SW = 353k
R_EL = 1.1M
Time (2ms/div)
Figure 4. 300Hz Output Waveform
Enable Function
The MIC4832 is disabled by connecting the external
resistor (Rsw) to GND. This turns off the switch
oscillator of the boost converter. Connecting the
external resistor (Rsw) to V_DD enables the oscillator
and turns on the device. The enable voltage should
rise or fall monotonically without interruption.
November 2007
6
M9999-111507-B