High Voltage EL Lamp Driver for Low Noise Applications

Transcription

1 HV8 HV8 Demo Kit Available High Voltage EL Lamp Driver for Low Noise Applications Features Patent pending audible noise reduction Patent pending lamp aging compensation 90V PP output voltage for higher brightness Patented output timing for high efficiency Single cell lithium ion compatible 0nA shutdown current Wide input voltage range.8v to.0v Separately adjustable lamp and converter frequencies Output voltage regulation Split supply capability Applications LCD backlighting Mobile cellular phones PDAs Handheld wireless communication products Global Positioning Systems (GPS) General Description The Supertex HV8 is a high voltage driver designed for driving Electroluminescent (EL) lamps of up to square inches. The input supply voltage range is from.8v to.0v. The device uses a single inductor and a minimum number of passive components. The nominal regulated output voltage that is applied to the EL lamp is ±9V. The chip can be enabled/disabled by connecting the resistor on R sw-osc to /ground. The HV8 has two internal oscillators, a switching MOSFET, and a high voltage EL lamp driver. The frequency for the switching MOSFET is set by an external resistor connected between the R sw-osc pin and the supply pin. The EL lamp driver frequency is set by an external resistor connected between R EL-osc pin and the pin. An external inductor is connected between the and pins or V IN for split supply applications. A µF capacitor is connected between C s and ground. The EL lamp is connected between V A and V B. The switching MOSFET charges the external inductor and discharges it into the capacitor at C s. The voltage at C s will start to increase. Once the voltage at C s reaches a nominal value of 9V, the switching MOSFET is turned OFF to conserve power. The outputs V A and V B are configured as an H bridge and are switching in opposite states to achieve ±9V across the EL lamp. Typical Application ON= OFF=0 Enable Signal Regulated Voltage= =V IN + _ R SW-osc R EL-osc Gnd V A V B 8 EL Lamp C IN HV8MG 0//0 Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the Supertex website: For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.

2 Electrical Characteristics DC Characteristics (Over recommended operating conditions unless otherwise specified, T A = C) Symbol Parameter Min Typ Max Units Conditions R DS(on) On-resistance of switching transistor.0 Ω I=00mA V Cs Max. output regulation voltage V =.8V to.0v V A V B Peak to Peak output voltage V =.8V to.0v I DDQ Quiescent supply current 0 na R SW-OSC =Low I DD Input current going into the pin 0 µa =.8V to.0v. See Figure. I IN Input current including inductor current 0 ma See Figure.* V Cs Output voltage on V Cs 8 V See Figure. f EL EL lamp frequency 0 0 Hz See Figure. f SW Switching transistor frequency 80 KHz See Figure. D Switching transistor duty cycle 88 % See Figure. * The inductor used is a 0µH Murata inductor, max DC resistance of 8.Ω, part # LQHCNK. HV8 Recommended Operating Conditions Symbol Parameter Min Typ Max Units Conditions Supply voltage.8.0 V f EL Output drive frequency KHz T A Operating temperature -0 8 C Enable/Disable Function Table Symbol Parameter Min Typ Max Units Conditions EN-L Logic input low voltage 0 0. V =.8V to.0v EN-H Logic input high voltage -0. V =.8V to.0v Absolute Maximum Ratings* Supply Voltage, -0.V to +.V Pin Configuration Operating Temperature Range -0 to +8 C Storage Temperature Range - C to +0 C MSOP-8 Power Dissipation 00mW Output voltage, V CS -0. to +0V Note: *Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Continuous operation of the device at the absolute rating level may affect device reliability. All voltages are referenced to device ground. R SW R EL MSOP-8 8 V A V B Ordering Information Package Options Gnd Top View Device MSOP-8 Die HV8 HV8MG* HV8X * Product supplied on 00 piece carrier tape reels.

3 Block Diagram HV8 R SW Switch Osc Q GND Disable + C _ VDD Vref Vsen Q High Voltage Level Translators V A Rel EL Osc Q V B Q Figure : Typical Application/Test Circuit ON= OFF=0 Enable Signal V IN = Equivalent to.0in lamp V IN + _.0µF Ω.0MΩ R SW-osc R EL-osc Gnd V A V B 8.0K SB0-0nF HV8MG 0µH 00V =0µH Murata (LQHCNK) SB0-=0V Sanyo Diode Typical Performance Device Lamp Size V IN I IN V CS f EL Brightness HV8MG.0 in.v 0mA 8V 0Hz.0ft-lm

4 HV8 Typical Performance Curves for Figure (EL Lamp=.0in, =.0V) VCS (V) Vcs vs Vin Vin (V) lin (ma) 9 Iin vs Vin..... Vin (V) Brightness vs Vin Iin vs Vcs Brightness (ft-lm)..... Vin (V) lin (ma) Vcs (V) 00 Iin, Vcs, Brightness vs Inductor Value Vcs 0 lin (ma), V CS (V) Iin Brightness lin Brightness (ft-lm) Inductor Value (µh) 0

5 External Component Description External Component Selection Guide Line HV8 Diode Cs Capacitor R EL-osc Fast reverse recovery diode, 0V Sanyo SB0- or equivalent. 0.00µF to 0.µF, 00V capacitor to GND is used to store the energy transferred from the inductor. The EL lamp frequency is controlled via an external R EL resistor connected between R EL-osc and of the device. The lamp frequency increases as R EL decreases. As the EL lamp frequency increases, the amount of current drawn from the battery will increase and the output voltage V CS will decrease. The color of the EL lamp is dependent upon its frequency. A MΩ resistor would provide lamp frequency of 0 to Hz. Decreasing the R EL-osc by a factor of will increase the lamp frequency by a factor of. R SW-osc Lx Inductor Lamp The switching frequency of the converter is controlled via an external resistor, R SW between R SW-osc and of the device. The switching frequency increases as R SW decreases. With a given inductor, as the switching frequency increases, the amount of current drawn from the battery will decrease and the output voltage, V CS, will also decrease. The inductor L x is used to boost the low input voltage by inductive flyback. When the internal switch is on, the inductor is being charged. When the internal switch is off, the charge stored in the inductor will be transferred to the high voltage capacitor. The energy stored in the capacitor is connected to the internal H-bridge and therefore to the EL lamp. In general, smaller value inductors, which can handle more current, are more suitable to drive larger size lamps. As the inductor value decreases, the switching frequency of the inductor (controlled by R SW ) should be increased to avoid saturation. 0µH Murata (LQHCN) inductors with 8.Ω series DC resistance is typically recommended. For inductors with thesame inductance value but with lower series DC resistance, lower R SW value is needed to prevent high current draw and inductor saturation. As the EL lamp size increases, more current will be drawn from the battery to maintain high voltage across the EL lamp. The input power, (V IN x I IN ), will also increase. If the input power is greater than the power dissipation of the package (00mW), an external resistor in series with one side of the lamp is recommended to help reduce the package power dissipation.

6 HV8 Split Supply Configuration The HV8 can also be used for handheld devices operating from a battery where a regulated voltage is available. This is shown in Figure. The regulated voltage can be used to run the internal logic of the HV8. The amount of current necessary to run the internal logic is 0µA Max at a of.0v. Therefore, the regulated voltage could easily provide the current without being loaded down. Enable/Disable Configuration The HV8 can be easily enabled and disabled via a logic control signal on the R SW and R EL resistors as shown in Figure below. The control signal can be from a microprocessor. R SW and R EL are typically very high values. Therefore, only 0 s of microamperes will be drawn from the logic signal when it is at a logic high (enable) state. When the microprocessor signal is high the device is enabled and when the signal is low, it is disabled. Figure : Split Supply and Enable/Disable Configuration ON= OFF=0 Enable Signal Battery Voltage=V IN Regulated Voltage= + _ R SW-osc R EL-osc Gnd V A V B 8 EL Lamp C IN HV8MG 00 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 0//0rev.0b Bordeaux Drive, Sunnyvale, CA 9089 TEL: (08) FAX: (08) -89

7 HV8 Application Note HV8 Application Note AN-H HV8 EL Lamp Driver Circuits for Low Audible Noise or High Brightness Applications by Roshanak Aflatouni, Applications Engineer This Application Note describes the method (patented) to reduce the audible noise generated by an EL (Electroluminescent) lamp used in mobile phone applications. This Application Note also provides example circuits as a guideline for applications with different lamp sizes, input voltages, and brightness requirements. For additional assistance in designing EL driver circuits, please refer to Application Notes AN-H (effect of external components on performance of Supertex EL drivers), Lamp Driver Circuits. When constructing and testing one of the driver circuits listed below, keep in mind that results may differ from those given due to lamp characteristics and component tolerance. When making component changes for circuit optimization, always remove supply voltages first. After making adjustments, bring up the supply voltage slowly starting from the minimum required device input voltage while monitoring input current. A sharp rise in current usually indicates a saturated inductor. Use a higher current rated inductor, a higher value inductor, or increase conversion frequency by lowering R SW-OSC value. Figure : Typical Application Circuit ON= OFF=0 Enable Signal V IN +.0µF R SW-osc R EL-osc Gnd V A V B 8 Series R SB0- EL Lamp HV8MG Sanyo Diode SB0-CP 0//0 Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the Supertex website: For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.

8 Mobile Phone Circuit for Audible Noise Reduction: HV8 Application Note The following table provides EL lamp audible noise and brightness for circuits which were designed based on typical EL lamp sizes for Mobile phone applications. See Figure, Table. Table Circuit Lamp Size Series R + Audible Noise Lamp Brightness ft-lm.in + 0K.dBA Cd/ m Supply Voltage V IN Lx Supply Current 0.mA.in + K.0dBA.9..mA.in + 0K 9.dBA.00..0V.0V.mA.in + K.dBA.8..mA.in + 00K.dBA mA.in + 0K.0dBA.90.9.mA.n + K 8.dBA...mA.in + 0K.0dBA. 9..mA.0V.0V.in + K.dBA.8.0.9mA.in + 9K.9dBA.0..mA.in + 0K.0dBA..9.mA Lamp Frequency 0Hz 0Hz Note:. All values are nominal. How to Minimize EL Lamp Audible Noise: The EL lamp, when lit, generates an audible noise. This is due to EL lamp construction which creates a major problem for applications where the EL lamp can be close to the ear such as cellular phones. The noisiest waveform is a square wave and the quietest waveform has been assumed to be a sine wave. After extensive research, Supertex has developed a waveform that is quieter than a sine wave. The waveform takes the shape of approximately RC time constants for rising and RC time constants for falling, where the C is the capacitance of the lamp and R is the external resistor used in series with one side of the lamp. This waveform has been proven to generate less noise than a sine wave. The audible noise from the EL lamp can be set at a desired level based on the series resistor value used with the lamp. We have chosen two commonly used lamp sizes for the mobile phones to demonstrate the effect of series resistor on the audible noise generated by the EL lamp. It is important to note that use of this resistor will reduce the voltage across the lamp. Reduction of voltage across the lamp will also has another effect on the overall performance of the Supertex EL drivers, age compensation (patented). This addresses a very important issue. EL lamp life is an important design concern to mobile phone manufacturers. As an EL lamp ages, its brightness is reduced and its capacitance is diminished. By using the RC model to reduce the audible noise generated by an EL lamp, the voltage across the lamp will increase as its capacitance diminishes. Hence the increase in voltage will compensate for the reduction of the brightness. As a result, it will extend an EL lamp s half-life (half the original brightness). Effect of Series Resistor on EL Lamp Audible Noise and Brightness: Increasing the value of the series resistor with the lamp will reduce the audible noise of an EL lamp as well as its brightness. This is due to the fact that the output voltage across the lamp will be reduced and the output waveform will have rounder edges. 8

9 HV8 Application Note Circuit Lamp Noise vs. Series R (.in EL Lamp) Lamp Noise (db) Series R (KΩ ) Brightness (cd/m ) Brightness vs. Series R (.in EL Lamp) Series R (KΩ ) Circuit Lamp Noise (db) Lamp Noise vs. Series R (.in EL Lamp) Series R (KΩ) Brightness vs. Series R (.in EL Lamp) Brightness (cd/m ) Series R (KΩ) 9

10 HV8 Application Note Typical HV8 Output waveform Before and After Noise Reduction: The following are actual scope pictures, which show the differential output waveform across the lamp, audible noise, and lamp light output for circuits and. Circuit Series R=0Ω 00V/div Differential Output Waveform across the lamp 0mV/div Audible Noise 00mV/div Light Output ms/div Series R=KΩ 00V/div Differential Output Waveform across the lamp 0mV/div Audible Noise 00mV/div Light Output ms/div 0

11 HV8 Application Note Circuit Series R=0Ω 00V/div Differential Output Waveform across the lamp 0mV/div Audible Noise 00mV/div Light Output ms/div Series R=KΩ 00V/div Differential Output Waveform across the lamp 0mV/div Audible Noise 00mV/div ms/div Light Output

12 Audible Noise Measurement Setup: HV8 Application Note The following setup was used to collect EL lamp audible noise data. An Oscilloscope/Spectrum analyzer was used to observe the differential output waveform, audible noise level (in mv), and light output (in mv) of the EL lamp. The EL lamp is placed in the anechoic chamber and a condenser microphone is placed 0mm away from the surface of the EL lamp. Driver Measurement Test Setup Oscilloscope/Spectrum Analyzer 0: probes Signal Conditioner Soundproof Anechoic Chamber EL Lamp Opto-acoustic Probe A-weighting filter NC Headphones EL Driver 0mm Scaling + - DC Supply Pneumatic Supports Scaling Low pass filter NC Drawing not to scale Opto-acoustic probe is battery powered to minimize electrical noise.

13 HV8 Application Note Circuit Selector Guide for Non Audible Noise Sensitive Applications: (Handheld products, PDAs, GPS, -way pagers, MP) No series resistor is used for the following circuits (R=0Ω). Also see Figure and Table. Table Circuit Lamp Size Lamp Brightness ft-lm Cd/ m Supply Voltage V IN Lx Supply Current Output Voltage Lamp Frequency..in.8...0V.V.V.mA.mA 8Vp-p 8Vp-p 0Hz. 0.in....0V.V.V.mA 0.9mA 8Vp-p 8Vp-p Hz.in V.V.9mA 80Vp-p Hz 0.9in...0V.0V 8.mA Vp-p 0Hz.in.8.8.0V.0V.9mA 8Vp-p 0Hz 8.0in.0..0V.0V.8mA 0Vp-p 0Hz 9.in...V.V.mA 8Vp-p 0Hz Note:. All values are nominal. Lamp brightness and current draw can vary by type and manufacturer. External components used for Circuits to 9: The following table provides the value for external components used in Figure. The manufacturer and part number for the inductor is also provided. If other value inductors are used, the circuit will need to be reoptimized. Table Circuit Value 0µ H 0µ H 0µ H Lx Inductor Manufacturer, Part. No. LQHCNK MuRata LQHCNK LQHCNK R R SW-OSC EL-OSC Value Capacitor Type 0K.0M 0K.0M 0K.M 0µ H 0µ H 0µ H 0µ H 8 0µ H 9 0µ H LQHCNK LQHCNK LQHCNK LQHCNK LQHMNK0 LQHMNK0 0K.M 0K.0M 0K.0M 0K.0M 0K.0M 0K.M

14 HV8 Application Note Inductor Selection: Different inductor values and/or from different manufacturers can be used in place of what is shown. However, the circuit will need to be reoptimized by changing the R SW-OSC value. Smaller R SW-OSC value needs to be used for inductors with lower series resistance. Lower amount of current will be drawn when using larger value inductors. But, for the same R SW-OSC value, a lower amount of energy will be transferred due to the higher series resistance of a larger value inductor. Hence, when larger value inductors with higher series resistance are used, the R SW-OSC value needs to be increased. It is very important to make a note of the saturation current of the inductor. If the saturation current of the inductor is lower than what the circuit/application requires, the inductor and/or IC will be damaged. Capacitor Selection: Different Capacitor types and value can be used in place of what is shown in circuits to 9. However, the use of a different Capacitor type will generate audible noise due to the piezo electric effect of materials used for their structure (such as XR and YU capacitors). A different value capacitor can be used. A larger value Capacitor (0nF) is recommended to be used for larger EL lamps and/or larger input voltage range. A smaller value Capacitor can be used as long as the over all efficiency of the circuit is not decreased. When using a smaller value Capacitor, the circuit will need to be reoptimized by using a smaller R SW-OSC value. 00 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 0//0AppNote.rev.b Bordeaux Drive, Sunnyvale, CA 9089 TEL: (08) FAX: (08) -89