Supertex hv857 datasheet and an-h43 application note

High Voltage EL Lamp Driver for
Available
Low Noise Applications
Features
General Description
❏ Patent pending audible noise reduction The Supertex HV857 is a high voltage driver designed for driving ❏ Patent pending lamp aging compensation Electroluminescent (EL) lamps of up to 5 square inches. Theinput supply voltage range is from 1.8V to 5.0V. The device uses ❏ 190V output voltage for higher brightness a single inductor and a minimum number of passive components.
❏ Patented output timing for high efficiency The nominal regulated output voltage that is applied to the EL lamp is ±95V. The chip can be enabled/disabled by connectingthe resistor on R The HV857 has two internal oscillators, a switching MOSFET, ❏ Wide input voltage range 1.8V to 5.0V and a high voltage EL lamp driver. The frequency for the ❏ Separately adjustable lamp and converter frequencies switching MOSFET is set by an external resistor connected driver frequency is set by an external resistor connected be- Applications
applications. A 0.003-0.1µF capacitor is connected between Csand ground. The EL lamp is connected between V and V .
The switching MOSFET charges the external inductor and discharges it into the capacitor at C . The voltage at C will start to increase. Once the voltage at C reaches a nominal value of 95V, the switching MOSFET is turned OFF to conserve power.
❏ Handheld wireless communication products The outputs V and V are configured as an H bridge and are switching in opposite states to achieve ±95V across the EL lamp.
Typical Application
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 liabilityindemnification 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 toworkmanship. 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.
Electrical Characteristics
DC Characteristics (Over recommended operating conditions unless otherwise specified, T =25°C)
Parameter
Conditions
* The inductor used is a 220µH Murata inductor, max DC resistance of 8.4Ω, part # LQH32CN221K21.
Recommended Operating Conditions
Parameter
Conditions
Enable/Disable Function Table
Parameter
Conditions
Absolute Maximum Ratings*
Pin Configuration
*Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these conditions is not implied. Continu-ous operation of the device at the absolute rating level may affect device reliability.
All voltages are referenced to device ground.
Ordering Information
Package Options
* Product supplied on 2500 piece carrier tape reels.
Block Diagram
Figure 1: Typical Application/Test Circuit
LX=220µH Murata (LQH32CN221K21)SB01-15=150V Sanyo Diode Typical Performance
Lamp Size
Brightness
Typical Performance Curves for Figure 1 (EL Lamp=3.0in2, V =3.0V)
External Component Description
External Component
Selection Guide Line
Fast reverse recovery diode, 150V Sanyo SB01-15 or equivalent.
0.003µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor.
The EL lamp frequency is controlled via an external R resistor connected between R device. The lamp frequency increases as R decreases. As the EL lamp frequency increases, the amount of current drawn from the battery will increase and the output voltage V lamp is dependent upon its frequency.
A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R increase the lamp frequency by a factor of 2.
The switching frequency of the converter is controlled via an external resistor, R of the device. The switching frequency increases as R 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 The inductor L 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 betransferred to the high voltage capacitor C . 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 theinductor (controlled by R ) should be increased to avoid saturation.
220µH Murata (LQH32CN221) inductors with 8.4Ω series DC resistance is typically recommended. Forinductors with thesame inductance value but with lower series DC resistance, lower R 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 acrossthe EL lamp. The input power, (V x I ), 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 recommendedto help reduce the package power dissipation.
Split Supply Configuration
Enable/Disable Configuration
The HV857 can also be used for handheld devices operating The HV857 can be easily enabled and disabled via a logic control from a battery where a regulated voltage is available. This is and R resistors as shown in Figure 2 below.
shown in Figure 2. The regulated voltage can be used to run The control signal can be from a microprocessor. R the internal logic of the HV857. The amount of current neces- are typically very high values. Therefore, only 10’s of microam- sary to run the internal logic is 150µA Max at a V peres will be drawn from the logic signal when it is at a logic high Therefore, the regulated voltage could easily provide the (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
TEL: (408) 222-8888 • FAX: (408) 222-4895 2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
Application Note
HV857 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 When constructing and testing one of the driver circuits listed reduce the audible noise generated by an EL (Electrolumines- below, keep in mind that results may differ from those given due cent) lamp used in mobile phone applications.
to lamp characteristics and component tolerance.
This Application Note also provides example circuits as a guide- When making component changes for circuit optimization, al- line for applications with different lamp sizes, input voltages, and ways remove supply voltages first. After making adjustments, bring up the supply voltage slowly starting from the minimumrequired device input voltage while monitoring input current. A For additional assistance in designing EL driver circuits, please sharp rise in current usually indicates a saturated inductor. Use refer to Application Notes AN-H33 (effect of external compo- a higher current rated inductor, a higher value inductor, or nents on performance of Supertex EL drivers), Lamp Driver increase conversion frequency by lowering R Figure 1: Typical Application Circuit
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 liabilityindemnification 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 toworkmanship. 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 theSupertex 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.
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.
How to Minimize EL Lamp
is diminished. By using the RC model to reduce the audible noisegenerated by an EL lamp, the voltage across the lamp will Audible Noise:
increase as its capacitance diminishes. Hence the increase in The EL lamp, when lit, generates an audible noise. This is due voltage will compensate for the reduction of the brightness. As a to EL lamp construction which creates a major problem for result, it will extend an EL lamp’s half-life (half the original applications where the EL lamp can be close to the ear such as cellular phones. The noisiest waveform is a square wave and thequietest waveform has been assumed to be a sine wave.
Effect of Series Resistor on EL
After extensive research, Supertex has developed a waveformthat is quieter than a sine wave. The waveform takes the shape Lamp Audible Noise and
of approximately 2RC time constants for rising and 2RC time Brightness:
constants for falling, where the C is the capacitance of the lampand R is the external resistor used in series with one side of the Increasing the value of the series resistor with the lamp will lamp. This waveform has been proven to generate less noise 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 willbe reduced and the output waveform will have rounder edges.
The audible noise from the EL lamp can be set at a desired levelbased on the series resistor value used with the lamp. We havechosen two commonly used lamp sizes for the mobile phones todemonstrate the effect of series resistor on the audible noisegenerated by the EL lamp. It is important to note that use of thisresistor will reduce the voltage across the lamp. Reduction ofvoltage across the lamp will also has another effect on the overallperformance of the Supertex EL drivers, age compensation(patented). This addresses a very important issue. EL lamp lifeis an important design concern to mobile phone manufacturers.
As an EL lamp ages, its brightness is reduced and its capacitance Circuit 1
Lamp Noise vs. Series R (2.6in2 EL Lamp)
Lamp Noise (dB)
Series R (KΩ )
Brightness vs. Series R (2.6in2 EL Lamp)
Brightness (cd/m
Series R (KΩ )
Circuit 2
Lamp Noise vs. Series R (1.7in2 EL Lamp)
Lamp Noise (dB)
Series R (KΩ)
Brightness vs. Series R (1.7in2 EL Lamp)
Brightness (cd/m
Series R (KΩ)
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
100V/div
Differential Output Waveform
across the lamp
50mV/div
Audible Noise
200mV/div
Light Output
Series R=65KΩ
Differential Output Waveform
100V/div
across the lamp
50mV/div
Audible Noise
200mV/div
Light Output
Circuit 2
Series R=0Ω
Differential Output Waveform
100V/div
across the lamp
20mV/div
Audible Noise
200mV/div
Light Output
Series R=55KΩ
Differential Output Waveform
100V/div
across the lamp
20mV/div
Audible Noise
200mV/div
Light Output
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
Opto-acoustic probe is battery poweredto minimize electrical noise.
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.
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.
L Inductor Selection:
C Capacitor Selection:
Different inductor values and/or from different manufacturers Different C Capacitor types and value can be used in place of can be used in place of what is shown. However, the circuit will what is shown in circuits 1 to 9. However, the use of a different C Capacitor type will generate audible noise due to the piezo value needs to be used for inductors with lower series electric effect of materials used for their structure (such as X7R resistance. Lower amount of current will be drawn when using larger value inductors. But, for the same R A different value capacitor can be used. A larger value C amount of energy will be transferred due to the higher series Capacitor (10nF) is recommended to be used for larger EL lamps resistance of a larger value inductor. Hence, when larger value and/or larger input voltage range. A smaller value C Capacitor inductors with higher series resistance are used, the R can be used as long as the over all efficiency of the circuit is not value needs to be increased. It is very important to make a note decreased. When using a smaller value C Capacitor, the circuit of the saturation current of the inductor. If the saturation current will need to be reoptimized by using a smaller R of the inductor is lower than what the circuit/application requires, the inductor and/or IC will be damaged.
TEL: (408) 222-8888 • FAX: (408) 222-4895 2003 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.

Source: http://www.futurel.bg/datasheets/4/HV857.pdf