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SP4422A Datasheet(PDF) 5 Page - Sipex Corporation |
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SP4422A Datasheet(HTML) 5 Page - Sipex Corporation |
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5 / 13 page  SP4422ADS/15 SP4422A Electroluminescent Lamp Driver © Copyright 2000 Sipex Corporation 5 When the energy from the coil is released, a high voltage spike is created triggering the SCR switches. The direction of current flow is determined by which SCR is enabled. One full cycle of the H-bridge will create 16 voltage steps from ground to 80V (typical) on pins 4 and 5 which are 180 degrees out of phase from each other (see figure 3 on page 9. A differential representation of the outputs is shown in figure 4 on page 9. Layout Considerations The SP4422A circuit board layout must observe careful analog precautions. For applications with noisy voltage power supplies a 0.1 µF low ESR decoupling capacitor must be connected from V DD to ground. Any high voltage traces should be isolated from any digital clock traces or enable lines. A solid ground plane connection is strongly recommended. All traces to the coil or to the high voltage outputs should be kept as short as possible to minimize capacitive coupling to digital clock lines and to reduce EMI emissions. Electroluminescent Technology What is electroluminescence? An EL lamp is basically a strip of plastic that is coated with a phosphorous material which emits light (fluoresces) when a high voltage (>40V) which was first applied across it, is removed or reversed. Long periods of DC voltages applied to the material tend to breakdown the material and reduce its lifetime. With these considerations in mind, the ideal signal to drive an EL lamp is a high voltage sine wave. Traditional approaches to achieving this type of waveform included discrete circuits incorporating a transformer, transistors, and several resistors and capacitors. This approach is large and bulky, and cannot be implemented in most hand held equipment. Sipex now offers low power single chip driver circuits specifically designed to drive small to medium sized electroluminescent panels. All that is required is one external inductor and capacitor. Electroluminescent backlighting is ideal when used with LCD displays, keypads, or other backlit readouts. Its main use is to illuminate displays in dim to dark conditions for momentary periods of time. EL lamps typically consume less than LEDs or bulbs making them ideal for battery powered products. Also, EL lamps are able to evenly light an area without creating "hot spots" in the display. The amount of light emitted is a function of the voltage applied to the lamp, the frequency at which it is applied, the lamp material used and its size, and lastly, the inductor used. There are many variables which can be optimized for specific applications. Sipex supplies characterization charts to aid the designer in selecting the optimum circuit configuration (see page 6). SP4422A Test Circuit 0.1 µF Low ESR Decoupling Capacitor NOTE: Keep high voltage traces short and away from VDD and clock lines Cap2 Cap1 VDD EL1 HON VSS Coil EL2 HON=V DD=ON HON=0V=OFF SP4422A VIN=3V NOTE: Keep coil as close to the SP4422A as possible + – COSC=100pF 100 Ω 17nF |
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