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TK65922MTL Datasheet(PDF) 9 Page - TOKO, Inc |
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TK65922MTL Datasheet(HTML) 9 Page - TOKO, Inc |
9 / 20 page May 2000 TOKO, Inc. Page 9 TK6592x clock is generated by dividing the high frequency clock by 128; this lower frequency clock corresponds to the drive frequency of the EL Lamp. The laser-trimmed oscillators are relatively insensitive to variations in temperature and supply voltage. Therefore, they provide good control of the lamp color emitted by the panel. The circuit below illustrates a typical application where the TK6592x is driving a 2-square-inch EL Lamp with a capacitance of approximately 12 nF. By keeping the ratio of the boost frequency and the H- Bridge frequency constant, the peak-to-peak output voltage from the TK6592x becomes primarily dependent upon the capacitance of the EL Lamp, the peak current threshold of the boost converter, and the value of the inductive element used in the boost converter. For the TK6592x, the peak current threshold is laser-trimmed to 52 mA. The capacitive load of the EL Lamp is a function of panel size and is typically fixed. Therefore, the high voltage output of the boost converter can be set to a desired voltage by selecting the appropriate value of the inductive element used in the boost converter. I PEAK = Boost Peak Current Threshold (52 mA) C EL = Capacitance of EL Lamp L = Inductance Value V HV = (IPEAK / 2) x (L /C EL) x 128 THEORY OF OPERATION An Electroluminescent (EL) Lamp is a strip of plastic, coated with a phosphorous material that emits light when a high voltage AC signal is applied to the terminals of the device. EL panels have the ability to light the entire panel uniformly. Because of this, they are gradually becoming more popular and widespread than LEDs. The amount of light emitted from an EL Lamp is typically proportional to the magnitude of the voltage applied to the lamp. Furthermore, the color of the light emitted by an EL Lamp is somewhat dependent upon the frequency of the applied drive signal. For most applications, a peak-to-peak voltage of 100 to 170 V, with a drive frequency of 175 to 400 Hz, provides optimal trade-off between lamp intensity and power consumption. The capacitance of the EL Panel is typically proportional to the size of the lamp (a 1 square inch EL Panel typically exhibits approximately 5 nF of capacitance load). The TK6592x series of devices has been optimized to drive EL panels, which are approximately 2-4 square inches in size. The Boost section of the TK6592x consists of a controller for stepping up a relatively low voltage (2.7 to 6 V) to a much higher voltage (50 to 90 V) needed to drive the EL Lamp. The boost section of the TK6592x uses a proprietary architecture which provides a relatively constant output power, independent of the input supply, without the need for sensing the high voltage output of the boost converter. By controlling the peak current through the switching element of the boost converter, the boost section provides a constant output power independent of the input supply. The H-Bridge section of the TK6592x switches the high voltage output of the boost converter to the two terminals of the EL Lamp. By alternately switching the terminals of the lamp between the high voltage supply and ground, the peak-to-peak voltage developed across the lamp is effectively twice the high voltage generated by boost converter. Furthermore, the TK6592x limits the magnitude of the drive currents through the H-Bridge switches in order to minimize the edge rates developed across the EL Lamp. This approach protects the EL Panel from large current spikes and reduces the likelihood of high frequency noise components being injected into neighboring circuitry. The Oscillator section of the TK6592x generates a fixed frequency clock source for the previously described Boost and H-Bridge sections, without the need for external components. The high frequency output of the oscillator is used for driving the boost controller. A lower frequency CEL 12 nF VIN C1 47 nF D1 EL + HV GND IND EL - VCC L1 FIGURE 1: TYPICAL APPLICATION |
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