IMP803
Pin Descriptions
Pin Number
1
2
3
4
5
6
Name
V
DD
R
SW-OSC
C
S
L
X
GND
V
B
Function
Positive voltage supply for the IMP803. Inductor L may be connected here or to a
separate unregulated supply.
Switch-mode resistor pin. Switching frequency is determined by an external resistor, R
SW
.
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 in a high-voltage bridge circuit with V
B
providing
the complementary connection to V
A
. The peak-to-peak AC voltage across the EL lamp is
thus two times V
CS
.
EL lamp drive. (See above)
The EL lamp oscillator frequency setting pin. The oscillator frequency is controlled
by external resistor R
EL
.
7
8
V
A
R
EL-OSC
External Components
External Component
Diode
Capacitor C
S
Resistor R
EL
Description and Selection Guide
Catch diode. A fast reverse recovery diode, with BV > 100, such as a 1N4148.
This is 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. This resistor, connected between the
R
EL-OSC
pin and V
DD
, provides an oscillator 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 2MΩ resistor between the R
EL-OSC
pin and the
V
DD
supply results in a lamp frequency around 350Hz: a 1MΩ resistor will give
≈700Hz.
Switching Oscillator frequency setting resistor. The switching oscillator resistor 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.
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 this internal switch opens, the inductor potential will forward-bias the catch
diode and the current will pass through the storage capacitor C
S
, charging it to a high voltage.
Smaller inductors are preferred to prevent saturation. As the value of the inductor
increases (and the series DC resistance of the inductor decreases), the switching frequency
set by R
SW
should 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.
Resistor R
SW
Inductor L
Lamp, R
CL
An external resistor (R
CL
) in series with the lamp will protect the output drivers from high transient
currents during lamp commutation.
High Voltages Present
The IMP803 generates high voltages and caution should
be exercised.
4
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© 2000 IMP, Inc.
IMP [ IMP, INC ]
