IMP525
Pin Descriptions
Pin Number
1
2
3
4
5
6
7
8
Disable Pad
Name
V
DD
R
SW-OSC
C
S
L
X
GND
V
B
V
A
R
EL-OSC
DIS
Function
Positive voltage supply for the IMP525. Inductor L may be connected here or to a
separate supply.
Switch-mode resistor pin. Switching frequency is determined by external resistor R
SW
,
connected between pin 2 and V
DD
.
Boost converter storage capacitor. The voltage across the EL lamp is equal to twice the
voltage at C
S
.
Connection to flyback inductance, L.
Ground pin.
EL lamp drive. The lamp is connected to a high-voltage bridge circuit with V
B
providing
the complementary connection to V
A
.
EL lamp drive. (See above)
The EL lamp oscillator frequency-setting pin. The frequency is controlled by resistor R
EL
,
connected from pin 8 to V
DD
.
Available only in die form. Setting DIS HIGH disables the chip.
External Components
External Component
Diode
Capacitor C
S
Resistor R
EL
Description and Selection Guide
A fast reverse recovery diode, with BV > 100, such as a 1N4148.
The high voltage capacitor that stores the inductive energy transferred through the
catch diode. A 100 volt capacitor between 10nF and 100nF is recommended.
The EL lamp oscillator frequency-setting resistor. R
EL
is connected between pin 8 and V
DD
,
providing a frequency inversely proportional to R
EL
; as R
EL
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 R
EL-OSC
pin and the V
DD
supply results in a lamp
frequency around 500Hz.
Switching Oscillator frequency-setting resistor. R
SW
is connected between the R
SW-OSC
pin and
the V
DD
supply. The switching frequency is inversely proportional to the resistor value, dropping
as the resistance increases.
This is an optional noise-suppression capacitor connected from ground to the R
SW-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
L
X
pin. When the switch opens, the inductor potential will forward-bias the diode
and the current will pass through to the storage capacitor C
S
, charging it to a high voltage.
As the value of the inductor is increased, the switching frequency set by R
SW
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 V
IN
,
will likely eliminate the need for C
SW
.
Resistor R
SW
Capacitor C
SW
Inductor L
4
IMP [ IMP, INC ]
