HV857 HV857 High Voltage EL Lamp Driver for Low Noise Applications Features General Description ❏ Patent pending audible noise reduction The Supertex HV857 is a high voltage driver designed for driving Electroluminescent (EL) lamps of up to 5 square inches. The input supply voltage range is from 1.8V to 5.0V. 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 ±95V. The chip can be enabled/disabled by connecting the resistor on Rsw-osc to VDD/ground. ❏ Patent pending lamp aging compensation ❏ 190VPP output voltage for higher brightness ❏ Patented output timing for high efficiency ❏ Single cell lithium ion compatible ❏ 150nA shutdown current The HV857 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 Rsw-osc pin and the supply pin VDD. The EL lamp driver frequency is set by an external resistor connected between REL-osc pin and the VDD pin. An external inductor is connected between the LX and VDD pins or VIN for split supply applications. A 0.003-0.1µF capacitor is connected between Cs and ground. The EL lamp is connected between VA and VB. ❏ Wide input voltage range 1.8V to 5.0V ❏ Separately adjustable lamp and converter frequencies ❏ Output voltage regulation ❏ Split supply capability Applications ❏ LCD backlighting The switching MOSFET charges the external inductor and discharges it into the capacitor at Cs. The voltage at Cs will start to increase. Once the voltage at Cs reaches a nominal value of 95V, the switching MOSFET is turned OFF to conserve power. The outputs VA and VB are configured as an H bridge and are switching in opposite states to achieve ±95V across the EL lamp. ❏ Mobile cellular phones ❏ PDAs ❏ Handheld wireless communication products ❏ Global Positioning Systems (GPS) Typical Application Enable Signal ON=VDD OFF=0 Regulated Voltage=VDD 1 VDD VA 8 2 RSW-osc VB 7 3 REL-osc CS 6 4 Gnd LX 5 EL Lamp VDD=VIN + _ CIN HV857MG LX CS 11/14/01 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: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website. 1 HV857 Electrical Characteristics DC Characteristics (Over recommended operating conditions unless otherwise specified, TA=25°C) Symbol Parameter Min Typ Max Units Conditions 6.0 Ω I=100mA V VDD=1.8V to 5.0V RDS(on) On-resistance of switching transistor VCs Max. output regulation voltage 85 95 105 VA – VB Peak to Peak output voltage 170 190 210 V VDD=1.8V to 5.0V IDDQ Quiescent VDD supply current 150 nA RSW-OSC=Low IDD Input current going into the VDD pin 150 µA VDD=1.8V to 5.0V. See Figure 1. IIN Input current including inductor current 20 25 mA See Figure 1.* VCs Output voltage on VCs 84 V See Figure 1. fEL EL lamp frequency Hz See Figure 1. fSW Switching transistor frequency 80 KHz See Figure 1. D Switching transistor duty cycle 88 % See Figure 1. 205 240 275 * The inductor used is a 220µH Murata inductor, max DC resistance of 8.4Ω, part # LQH32CN221K21. Recommended Operating Conditions Symbol Parameter VDD Supply voltage fEL Output drive frequency TA Operating temperature Min Typ Max Units 5.0 V 1 KHz 85 °C Max Units 1.8 -40 Conditions Enable/Disable Function Table Symbol Parameter Min Typ Conditions EN-L Logic input low voltage 0 0.2 V VDD=1.8V to 5.0V EN-H Logic input high voltage VDD-0.2 VDD V VDD=1.8V to 5.0V Pin Configuration Absolute Maximum Ratings* Supply Voltage, VDD -0.5V to +6.5V Operating Temperature Range Storage Temperature Range -40° to +85°C -65°C to +150°C MSOP-8 Power Dissipation 300mW Output voltage, VCS VDD 1 8 VA RSW 2 7 VB REL 3 6 CS Gnd 4 5 LX -0.5 to +120V 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. MSOP-8 Ordering Information Top View Package Options Device MSOP-8 Die HV857 HV857MG* HV857X * Product supplied on 2500 piece carrier tape reels. 2 HV857 Block Diagram LX VDD CS RSW Switch Osc Q GND + C _ Disable VA Vsen Q High Voltage Level Translators Vref VDD Q EL Osc Rel VB Q Figure 1: Typical Application/Test Circuit Equivalent to 3.0in2 lamp Enable Signal ON=VDD OFF=0 VIN=VDD 2.0K VDD 1 VDD VA 8 2 RSW-osc VB 7 3 REL-osc CS 6 4 Gnd LX 5 Ω 10nF + VIN _ 2.0MΩ 1.0µF HV857MG SB01-15 220µH 3.3nF 100V LX=220µH Murata (LQH32CN221K21) SB01-15=150V Sanyo Diode Typical Performance Device HV857MG Lamp Size 3.0 in2 VIN IIN VCS fEL Brightness 3.3V 20mA 84V 240Hz 6.0ft-lm 3 HV857 Typical Performance Curves for Figure 1 (EL Lamp=3.0in2, VDD=3.0V) Vcs vs Vin Iin vs Vin 25 23 85 lin (mA) 75 65 55 1.5 2.5 3.5 4.5 21 19 17 15 13 1.5 5.5 2.5 3.5 Brightness vs Vin 5.5 85 95 Iin vs Vcs 7 6 24 5 4 3 2 1 1.5 20 lin (mA) 22 18 16 14 2.5 3.5 4.5 55 5.5 65 75 Vcs (V) Vin (V) Iin, Vcs, Brightness vs Inductor Value 7 100 90 6 Vcs 80 5 70 lin (mA), VCS (V) Brightness (ft-lm) 4.5 Vin (V) Vin (V) 60 Brightness 4 50 3 40 Iin 30 2 lin 20 1 10 0 0 100 150 200 250 300 350 Inductor Value (µH) 4 400 450 500 550 600 Brightness (ft-lm) VCS (V) 95 HV857 External Component Description External Component Selection Guide Line Diode Fast reverse recovery diode, 150V Sanyo SB01-15 or equivalent. Cs Capacitor 0.003µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor. REL-osc The EL lamp frequency is controlled via an external REL resistor connected between REL-osc and VDD of the device. The lamp frequency increases as REL decreases. As the EL lamp frequency increases, the amount of current drawn from the battery will increase and the output voltage VCS will decrease. The color of the EL lamp is dependent upon its frequency. A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the REL-osc by a factor of 2 will increase the lamp frequency by a factor of 2. RSW-osc The switching frequency of the converter is controlled via an external resistor, RSW between RSW-osc and VDD of the device. The switching frequency increases as RSW decreases. With a given inductor, as the switching frequency increases, the amount of current drawn from the battery will decrease and the output voltage, VCS, will also decrease. Lx Inductor The inductor Lx 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 CS. 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 RSW) should be increased to avoid saturation. 220µH Murata (LQH32CN221) inductors with 8.4Ω series DC resistance is typically recommended. For inductors with thesame inductance value but with lower series DC resistance, lower RSW value is needed to prevent high current draw and inductor saturation. Lamp 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, (VIN x IIN), will also increase. If the input power is greater than the power dissipation of the package (300mW), an external resistor in series with one side of the lamp is recommended to help reduce the package power dissipation. 5 HV857 Split Supply Configuration Enable/Disable Configuration The HV857 can also be used for handheld devices operating from a battery where a regulated voltage is available. This is shown in Figure 2. The regulated voltage can be used to run the internal logic of the HV857. The amount of current necessary to run the internal logic is 150µA Max at a VDD of 3.0V. Therefore, the regulated voltage could easily provide the current without being loaded down. The HV857 can be easily enabled and disabled via a logic control signal on the RSW and REL resistors as shown in Figure 2 below. The control signal can be from a microprocessor. RSW and REL are typically very high values. Therefore, only 10’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 2: Split Supply and Enable/Disable Configuration Enable Signal ON=VDD OFF=0 Regulated Voltage=VDD 1 VDD VA 8 2 RSW-osc VB 7 3 REL-osc CS 6 4 Gnd LX 5 EL Lamp Battery Voltage=VIN + _ CIN HV857MG LX CS 11/14/01rev.10 ©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 6 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 • FAX: (408) 222-4895 www.supertex.com HV857 Application Note HV857 Application Note AN-H43 HV857 EL Lamp Driver Circuits for Low Audible Noise or High Brightness Applications by Roshanak Aflatouni, Applications Engineer This Application Note describes the method (patent pending) to reduce the audible noise generated by an EL (Electroluminescent) lamp used in mobile phone applications. 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. This Application Note also provides example circuits as a guideline for applications with different lamp sizes, input voltages, and brightness requirements. 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 RSW-OSC value. For additional assistance in designing EL driver circuits, please refer to Application Notes AN-H33 (effect of external components on performance of Supertex EL drivers), Lamp Driver Circuits. Figure 1: Typical Application Circuit Enable Signal ON=VDD OFF=0 Series R VDD 1 VDD VA 8 VB 7 EL Lamp 2 RSW-osc + VIN 1.0µF 3 REL-osc CS 6 4 Gnd LX 5 HV857MG SB01-15 LX CS Sanyo Diode SB01-15CP 11/27/01 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: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website. 7 HV857 Application Note Mobile Phone Circuit for Audible Noise Reduction:1 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 1, Table 3. Table 1 Circuit Lamp Size + Series R 2 2.6in + 0K ft-lm Cd/m2 Supply Voltage VDD Lx Supply Current 8.09 27.7 20.6mA 32.0dBA 6.93 23.7 23.3mA 2 2.6in + 50K 29.2dBA 5.00 17.1 2.6in2 + 75K 26.7dBA 3.83 13.1 22.6mA 2.6in2 + 100K 23.3dBA 2.80 9.56 21.3mA 2 32.0dBA 6.90 23.59 13.4mA 2 1.7n + 25K 28.3dBA 6.35 21.73 15.5mA 2 3.0V Lamp Frequency VIN 35.1dBA 1.7in + 0K 2 Lamp Brightness 2 2.6in + 25K 1 Audible Noise 3.0V 23.5mA 1.7in + 50K 26.0dBA 5.72 19.55 1.7in2 + 75K 24.4dBA 4.85 16.60 1.7in2 + 95K 22.9dBA 4.20 14.35 16.5mA 1.7in2 + 120K 21.0dBA 3.42 11.69 15.6mA 250Hz 16.6mA 3.0V 3.0V 16.9mA 250Hz Note: 1. All values are nominal. 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). 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 2RC time constants for rising and 2RC 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. 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. 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 (patent pending). This addresses a very important issue. EL lamp life is an important design concern to mobile phone manufacturers. 8 HV857 Application Note Circuit 1 Lamp Noise (dB) Lamp Noise vs. Series R (2.6in2 EL Lamp) 40 35 30 25 20 15 10 0 20 40 60 80 100 120 140 160 Series R (KΩ ) Brightness (cd/m2) Brightness vs. Series R (2.6in2 EL Lamp) 30 25 20 15 10 5 0 0 20 40 60 80 100 120 140 160 Series R (KΩ ) Circuit 2 Lamp Noise (dB) Lamp Noise vs. Series R (1.7in2 EL Lamp) 40 35 30 25 20 15 10 0 20 40 60 80 100 120 140 160 Series R (KΩ) Brightness (cd/m2) Brightness vs. Series R (1.7in2 EL Lamp) 25 20 15 10 5 0 0 20 40 60 80 100 120 140 160 Series R (KΩ) 9 HV857 Application Note Typical HV857 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 1 and 2. Circuit 1 Series R=0Ω Differential Output Waveform across the lamp 100V/div Audible Noise 50mV/div Light Output 200mV/div 1ms/div Series R=65KΩ Differential Output Waveform across the lamp 100V/div Audible Noise 50mV/div Light Output 200mV/div 1ms/div 10 HV857 Application Note Circuit 2 Series R=0Ω Differential Output Waveform across the lamp 100V/div 20mV/div Audible Noise 200mV/div Light Output 1ms/div Series R=55KΩ Differential Output Waveform across the lamp 100V/div 20mV/div Audible Noise Light Output 200mV/div 1ms/div 11 HV857 Application Note Audible Noise Measurement Setup: 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 10mm away from the surface of the EL lamp. Driver Measurement Test Setup Oscilloscope/Spectrum Analyzer 10:1 probes Signal Conditioner Soundproof Anechoic Chamber Headphones A-weighting filter EL Lamp Opto-acoustic Probe NC 10mm EL Driver Scaling + - DC Supply Drawing not to scale Scaling Low pass filter Pneumatic Supports Opto-acoustic probe is battery powered to minimize electrical noise. 12 NC HV857 Application Note Circuit Selector Guide for Non Audible Noise Sensitive Applications:1 (Handheld products, PDAs, GPS, 2-way pagers, MP3) No series resistor is used for the following circuits (R=0Ω). Also see Figure 1 and Table 3. Table 2 Circuit Lamp Brightness Lamp Size Supply Voltage ft-lm Cd/m2 VDD VIN Lx Supply Current Output Voltage Lamp Frequency 3 1.3in2 9.38 32.10 3.3V 3.3V 12.9mA 180Vp-p 357Hz 4 1.7in2 4.44 4.48 15.2 15.31 3.0V 3.2V 4.2V 7.4mA 5.7mA 182Vp-p 186Vp-p 160Hz 5 1.7in2 12.0 13.2 41.6 45.3 3.0V 3.2V 4.2V 23.7mA 20.9mA 168Vp-p 178Vp-p 475Hz 6 0.93in2 7.74 26.51 3.0V 3.0V 8.3mA 175Vp-p 250Hz 7 3.1in2 7.84 26.87 5.0V 5.0V 17.9mA 184Vp-p 250Hz 8 4.0in2 7.50 25.7 3.0V 3.0V 25.8mA 160Vp-p 250Hz 9 5.2in2 4.77 16.34 3.3V 3.3V 21.2mA 168Vp-p 160Hz Note: 1. All values are nominal. Lamp brightness and current draw can vary by type and manufacturer. External components used for Circuits 1 to 9: The following table provides the value for external components used in Figure 1. 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 3 CS Capacitor Lx Inductor Circuit RSW-OSC REL-OSC Value Manufacturer, Part. No. 1 220µH MuRata, LQH32CN221K21 560K 2 220µH MuRata LQH32CN221K21 3 220µH 4 Value Type 2.0M 3.3nF NPO 560K 2.0M 3.3nF NPO MuRata, LQH32CN221K21 560K 1.5M 3.3nF NPO 220µH MuRata, LQH32CN221K21 330K 3.3M 3.3nF NPO 5 220µH MuRata, LQH32CN221K21 560K 1.0M 3.3nF NPO 6 220µH MuRata, LQH32CN221K21 560K 2.0M 3.3nF NPO 7 220µH MuRata, LQH32CN221K21 560K 2.0M 3.3nF NPO 8 220µH MuRata, LQH43MN221K01 560K 2.0M 3.3nF NPO 9 220µH MuRata, LQH43MN221K01 560K 3.3M 3.3nF NPO 13 HV857 Application Note LX Inductor Selection: CS Capacitor 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 RSW-OSC value. Smaller RSW-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 RSW-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 RSW-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. Different CS Capacitor types and value can be used in place of what is shown in circuits 1 to 9. However, the use of a different CS Capacitor type will generate audible noise due to the piezo electric effect of materials used for their structure (such as X7R and 5YU capacitors). A different value capacitor can be used. A larger value CS Capacitor (10nF) is recommended to be used for larger EL lamps and/or larger input voltage range. A smaller value CS Capacitor can be used as long as the over all efficiency of the circuit is not decreased. When using a smaller value CS Capacitor, the circuit will need to be reoptimized by using a smaller RSW-OSC value. 11/27/01AppNote.rev.3 ©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited. 14 1235 Bordeaux Drive, Sunnyvale, CA 94089 TEL: (408) 744-0100 • FAX: (408) 222-4895 www.supertex.com