IMP527
Pin Descriptions
Pin Number
Name
VDD
Function
1
Positive voltage supply for the IMP527. Inductor L may be connected here or to a
separate supply.
2
3
RSW-OSC
CS
Switch-mode resistor pin. Switching frequency is determined by external resistor RSW,
connected between pin 2 and VDD
.
Boost converter storage capacitor. The voltage across the EL lamp is equal to twice the
voltage at CS.
4
5
6
LX
GND
VB
Connection to flyback inductance, L.
Ground pin.
EL lamp drive. The lamp is connected to a high-voltage bridge circuit with VB providing
the complementary connection to V .
A
7
8
V
EL lamp drive. (See above)
A
REL-OSC
The EL lamp oscillator frequency-setting pin. The frequency is controlled by resistor REL
,
connected from pin 8 to VDD
.
Disable Pad
DIS
Available only in die form. Setting DIS HIGH disables the chip.
External Components
External Component
Diode
Description and Selection Guide
A fast reverse recovery diode, with BV > 100, such as a 1N4148.
Capacitor CS
The high voltage capacitor that stores the inductive energy transferred through the
catch diode. A 100 volt capacitor between 10nF and 100nF is recommended.
Resistor REL
The EL lamp oscillator frequency-setting resistor. REL is connected between pin 8 and VDD,
providing a frequency inversely proportional to REL; as REL increases, the EL lamp frequency
decreases along with the current drawn by the lamp. Lamp color is also determined by this
frequency. A 1MΩ resistor between the REL-OSC pin and the VDD supply results in a lamp
frequency around 500Hz.
Resistor RSW
Switching Oscillator frequency-setting resistor. RSW is connected between the RSW-OSC pin and
the VDD supply. The switching frequency is inversely proportional to the resistor value, dropping
as the resistance increases.
Capacitor CSW
Inductor L
This is an optional noise-suppression capacitor connected from ground to the RSW-OSC pin.
A 100pF capacitor is recommended.
The inductor provides the voltage boost needed by means of inductive “flyback”. The internal
MOSFET switch alternately opens and closes the ground connection for the inductor at the
LX pin. When the switch opens, the inductor potential will forward-bias the diode
and the current will pass through to the storage capacitor CS, charging it to a high voltage.
As the value of the inductor is increased, the switching frequency set by RSW should also be
increased to prevent saturation. In general, smaller value inductors that can handle more current
are more desirable when larger-area EL lamps must be driven.
A small electrolytic capacitor (10µF, 16V), normally present across the inductor supply VIN,
will likely eliminate the need for CSW
.
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