|Title||LEDs/Segment Display Drivers|
|Description||el Plus Piezo Driver|
|Datasheet||Download SP4501EN datasheet
s Integrated EL Plus Piezo Driver For Portable Electronic Devices s Reduces System Cost, Size & Component Count to +6.0V Battery Operation s A Single External Coil Drives Both the EL Lamp and Piezotransducer Circuitry s Piezotransducer Can Be Driven By an External Clock or Internal Clock s A Single Resistor Controls the Internal Oscillator s DC-to-AC Inverter Produces 200VP-P to Drive EL Lamps s DC-to-AC Inverter Produces Waveform to Drive Piezotransducer s Low Current Standby Mode Draws Less than 1µAAPPLICATIONS s PDA's s Pagers s GPS s Hand Held Medical Devices
DESCRIPTION The SP4501 provides designers with both an electroluminescent lamp driver for backlighting and a piezotransducer driver to generate audio alert tones. The integration an EL lamp driver and a piezotransducer driver in a single cost-effective IC reduces system cost, board space requirements and component count. The SP4501 is ideal for portable applications such as pagers, electronic games, PDAs, medical equipment, and designs with liquid crystal displays, keypads, and backlit readouts. The SP4501 will operate from to +6.0V source. The device features a low power standby mode which draws less than 1µA (typical). The frequency of the internal oscillator is set with a single external resistor. The piezotranducer driver can be driven with the internally generated clock signal or an external clock signal provided by the designer. A single inductor is required to generate the high voltage AC used to drive the EL lamp and the piezotransducer. All input pins are ESD protected with diodes to VDD and VSS.
These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Power Supply, VDD.................................................7.0V Input Voltages, to (VDD+0.3V) Lamp Outputs...................................................220VP-P Operating to +85°C Storage to +150°C Power Dissipation Per Package 14-pin SOIC (derate 8.33mW/°C above +70°C)....................700mW 14-pin TSSOP (derate 9.96mW/°C above +70°C)....................800mW
STORAGE CONSIDERATIONS Storage in a low humidity environment is preferred. Large high density plastic packages are moisture sensitive and should be stored in Dry Vapor Barrier Bags. Prior to usage, the parts should remain bagged and stored below 40°C and 60%RH. If the parts are removed from the bag, they should be used within 48 hours or stored in an environment at or below 20%RH. If the above conditions cannot be followed, the parts should be baked for four hours 125°C in order remove moisture prior to soldering. Sipex ships product in Dry Vapor Barrier Bags with a humidity indicator card and desiccant pack. The humidity indicator should be below 30%RH. The information furnished by Sipex has been carefully reviewed for accuracy and reliability. Its application or use, however, is solely the responsibility of the user. No responsibility for the use of this information become part of the terms and conditions of any subsequent sales agreement with Sipex. Specifications are subject to change without no responsibility for any infringement of patents or other rights of third parties which may result from its use. No license or other proprietary rights are granted by implication or otherwise under any patent or patent rights of Sipex Corporation.SPECIFICATIONS
VDD = 470µH, CLAMP = 8nF, CPZ = 16nF, CINT = 1800pF ROSC = 500k, and TAMB = 25°C unless otherwise noted.
PARAMETER Supply Voltage, VDD Supply Current, ICOIL+IDD Standby Current Input Voltage for ELEN and PZEN, PZCK, PZCK LOW HIGH Input Impedance ELEN and PZCK PZEN and PZCK Inductor Drive Coil Frequency, fOSC Duty Cycle of fOSC Peak Coil Current EL Lamp/ Piezo Driver Output Piezo Output Voltage, VPZ
fpiezo = 3.1kHz, PZEN = HIGH; TAMB = +25OC TAMB to +85OC TAMB = +25OC TAMB to +85OC TAMB = +25OC TAMB to +85OC PZEN = HIGH; TAMB = +25OC TAMB to +85OCLamp Output Voltage, VEL EL Lamp Frequency, fLAMP Piezo Frequency, fPZ 289 2.3
Electroluminescent Technology An EL lamp consists of a thin layer of phosphorous material sandwiched between two strips of plastic which emits light (flouresces) when a high voltage AC signal is applied across it. It behaves primarily as a capacitive load. Long periods of DC voltage applied to the material tend to reduce its lifetime. With these conditions in mind, the ideal signal to drive an EL lamp is a high voltage sine wave. Traditional approaches to achieve this type of waveform include discrete circuits incorporating a transformer, transistors and several resistors and capacitors. This approach is large and bulky and cannot be implemented in most handheld equipment. Sipex offers low power single chip driver circuits specifically designed to drive small to medium sized electroluminescent panels. Sipex EL drivers provide a differential AC voltage without a DC offset to maximize EL lamp lifetime. The only additional components required for the EL driver circuitry are an inductor, resistor and capacitor. Electroluminescent backlighting is ideal when used with LCD displays, keypads or other backlit readouts. EL lamps uniformly light an area without creating any undesirable "hot spots" in the display. Also, an EL lamp typically consumes less power that LED's or incandescent bulbs in similar lighting situations. These features make EL ideal for attractive, battery powered products. THEORY OF OPERATION Coil Switch The SP4501 has an inductor-based boost converter to generate the high voltage used to drive the EL lamp. Energy is stored in the inductor according to the equation 1/2 (LIpk2) where Ipk = (tON) (VBATT - VCEsat) /L. An internal oscillator controls the coil switch. During the time the coil switch is on, the coil is connected between VDD and the saturation voltage of the coil switch and a magnetic field develops in the coil. When the coil switch turns off, the switch opens, the magnetic field collapses and the voltage across the coil rises.
The internal diode forward biases when the coil voltage rises above the H-Bridge voltage and the energy enters the EL lamp. Each pulse increases the voltage across the lamp in discrete steps. As the voltage approaches its maximum, the steps become smaller. (see figure 4). The brightness of the EL lamp output is directly related to energy recovery in the boost converter. There are many variations among coils such as magnetic core differences, winding differences and parasitic capacitances. For suggested coil suppliers refer to page 10. Oscillator The internal oscillator generates a high frequency clock used by the boost converter and H-Bridge. An external resistor from VDD to ROSC sets the oscillator frequency. Typically a 500k resistor sets the frequency to 45.7kHz. The high frequency clock directly controls the coil switch. This high frequency clock is divided 128 to generate a low frequency clock which controls the EL H-Bridge and sets the EL lamp frequency. The high frequency clock is divided 16 to create a medium frequency clock to drive the piezo H-Bridge. The oscillator has low sensitivity to temperature and supply voltage variations, increasing the performance of the EL driver over the operating parameters. Dual H-Bridge The H-Bridge consists of two SCR structures and two NPN transistors that control how the lamp is charged. Setting ELEN to HIGH activates the EL H-Bridge. The EL driver illuminates the lamp by applying the high voltage supply of the boost converter to the lamp terminals through the H-Bridge and then switching the terminal polarity between the high voltage supply and ground at a constant frequency. This applies an AC voltage to the lamp that is twice the peak output voltage of the boost driver. An AC voltage greater than the 40V across the terminals of the lamp is necessary to adequately illuminate the EL lamp. The piezo driver output applies an AC voltage to the piezotransducer in a similar manner. The piezo driver operates in two modes.
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