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HV857
HV857 High Voltage EL Lamp Driver for Low Noise Applications
Features
Patent pending audible noise reduction 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 Wide input voltage range 1.8V to 5.0V Separately adjustable lamp and converter frequencies Output voltage regulation Split supply capability
General Description
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. 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 0.003-0.1F capacitor is connected between Cs and ground. The EL lamp is connected between VA and VB. 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.
Applications
LCD backlighting Mobile cellular phones PDAs Handheld wireless communication products Global Positioning Systems (GPS)
Typical Application
ON=VDD OFF=0 Regulated Voltage=VDD Enable Signal
1 VDD 2 RSW-osc
VA VB
8
EL Lamp
7
VDD=VIN
+ _
CIN
3 REL-osc 4 Gnd
CS 6 LX 5 LX CS
HV857MG
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=25C)
Symbol RDS(on) VCs VA - VB IDDQ IDD IIN VCs fEL fSW D Parameter On-resistance of switching transistor Max. output regulation voltage Peak to Peak output voltage Quiescent VDD supply current Input current going into the VDD pin Input current including inductor current Output voltage on VCs EL lamp frequency Switching transistor frequency Switching transistor duty cycle 205 20 84 240 80 88 275 85 170 95 190 Min Typ Max 6.0 105 210 150 150 25 Units V V nA A mA V Hz KHz % I=100mA VDD=1.8V to 5.0V VDD=1.8V to 5.0V RSW-OSC=Low VDD=1.8V to 5.0V. See Figure 1. See Figure 1.* See Figure 1. See Figure 1. See Figure 1. See Figure 1. Conditions
* The inductor used is a 220H Murata inductor, max DC resistance of 8.4, part # LQH32CN221K21.
Recommended Operating Conditions
Symbol VDD fEL TA Supply voltage Output drive frequency Operating temperature -40 Parameter Min 1.8 Typ Max 5.0 1 85 Units V KHz C Conditions
Enable/Disable Function Table
Symbol EN-L EN-H Parameter Logic input low voltage Logic input high voltage Min 0 VDD-0.2 Typ Max 0.2 VDD Units V V Conditions VDD=1.8V to 5.0V VDD=1.8V to 5.0V
Absolute Maximum Ratings*
Supply Voltage, VDD Operating Temperature Range Storage Temperature Range MSOP-8 Power Dissipation Output voltage, VCS -0.5V to +6.5V -40 to +85C -65C to +150C 300mW -0.5 to +120V
Pin Configuration
VDD RSW REL Gnd
1 2
8 7
VA VB CS LX
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
3 4
Top View
6 5
Ordering Information
Package Options Device HV857 MSOP-8 HV857MG* Die HV857X
* Product supplied on 2500 piece carrier tape reels.
2
HV857
Block Diagram
LX VDD CS RSW Switch Osc
Q
GND Disable
+ C _
Vsen Vref High Voltage Level Translators
Q
VA
VDD
Q
Rel
EL Osc
Q
VB
Figure 1: Typical Application/Test Circuit
ON=VDD OFF=0 VDD Enable Signal VIN=VDD 2.0K Equivalent to 3.0in2 lamp
1 VDD 2 RSW-osc
VA VB
8
10nF
7
+
VIN
_
1.0F
3 REL-osc
2.0M
CS 6 LX 5 SB01-15
4 Gnd
HV857MG
220H 3.3nF 100V
LX=220H Murata (LQH32CN221K21) SB01-15=150V Sanyo Diode
Typical Performance
Device HV857MG Lamp Size 3.0 in2 VIN 3.3V IIN 20mA VCS 84V fEL 240Hz Brightness 6.0ft-lm
3
HV857
Typical Performance Curves for Figure 1 (EL Lamp=3.0in2, VDD=3.0V)
Vcs vs Vin 95
VCS (V) lin (mA)
Iin vs Vin 25 23 21 19 17 15 13 1.5
85 75 65 55 1.5 2.5 3.5 Vin (V) 4.5 5.5
2.5
3.5 Vin (V)
4.5
5.5
Brightness vs Vin 7 6 5 4 3 2 1 1.5
lin (mA)
Iin vs Vcs 24 22 20 18 16 14
Brightness (ft-lm)
2.5
3.5 Vin (V)
4.5
5.5
55
65
75 Vcs (V)
85
95
Iin, Vcs, Brightness vs Inductor Value 100 90 6 80 70 Vcs 5 Brightness 4 3 Iin 2 7
60 50 40 30 20 10 0 100
lin
1 0
150
200
250
300
350
400
450
500
550
600
Inductor Value (H)
4
Brightness (ft-lm)
lin (mA), VCS (V)
HV857
External Component Description
External Component Diode Cs Capacitor REL-osc Selection Guide Line Fast reverse recovery diode, 150V Sanyo SB01-15 or equivalent. 0.003F to 0.1F, 100V capacitor to GND is used to store the energy transferred from the inductor. 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 2M 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. 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. 220H Murata (LQH32CN221) inductors with 8.4 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.
Lx Inductor
5
HV857
Split Supply 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 150A Max at a VDD of 3.0V. Therefore, the regulated voltage could easily provide the current without being loaded down.
Enable/Disable Configuration
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
ON=VDD OFF=0 Regulated Voltage=VDD Enable Signal
1 VDD 2 RSW-osc
VA VB
8
EL Lamp
7
Battery Voltage=VIN
+ _
CIN
3 REL-osc 4 Gnd
CS 6 LX 5 LX CS
HV857MG
11/14/01rev.10
(c)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 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. 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-H33 (effect of external components on performance of Supertex EL drivers), Lamp Driver Circuits.
HV857 Application Note
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 RSW-OSC value.
Figure 1: Typical Application Circuit
ON=VDD OFF=0 VDD
Enable Signal Series R
1 VDD 2
RSW-osc
VA VB
8
EL Lamp
7
+
VIN 1.0F
3 REL-osc 4 Gnd
CS 6 LX 5 SB01-15
HV857MG
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 2.6in + 0K 2.6in + 25K 1 2.6in + 50K 2.6in2 + 75K 2.6in2 + 100K 1.7in + 0K 1.7n + 25K 1.7in + 50K 2 1.7in2 + 75K 1.7in2 + 95K 1.7in2 + 120K
Note: 1. All values are nominal.
2 2 2 2 2 2
Audible Noise 35.1dBA 32.0dBA 29.2dBA 26.7dBA 23.3dBA 32.0dBA 28.3dBA 26.0dBA 24.4dBA 22.9dBA 21.0dBA
Lamp Brightness ft-lm 8.09 6.93 5.00 3.83 2.80 6.90 6.35 5.72 4.85 4.20 3.42 Cd/m2 27.7 23.7 17.1 13.1 9.56 23.59 21.73 19.55 16.60 14.35 11.69
Supply Voltage VDD VIN
Lx Supply Current 20.6mA 23.3mA
Lamp Frequency
3.0V
3.0V
23.5mA 22.6mA 21.3mA 13.4mA 15.5mA 16.6mA
250Hz
3.0V
3.0V
16.9mA 16.5mA 15.6mA
250Hz
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. 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.
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
HV857 Application Note
Circuit 1
Lamp Noise vs. Series R (2.6in2 EL Lamp)
Lamp Noise (dB)
40 35 30 25 20 15 10 0 20 40 60 80 100 120 140 160 Series R (K )
Brightness vs. Series R (2.6in2 EL Lamp)
Brightness (cd/m2)
30 25 20 15 10 5 0 0 20 40 60 80 100 120 140 160 Series R (K )
Circuit 2
40 35 30 25 20 15 10
Lamp Noise (dB)
Lamp Noise vs. Series R (1.7in2 EL Lamp)
0
20
40
60
80
100 120 140 160
Series R (K)
Brightness vs. Series R (1.7in2 EL Lamp)
Brightness (cd/m2)
25 20 15 10 5 0 0 20 40 60 80 100 120 140 160 Series R (K)
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=0
100V/div
Differential Output Waveform across the lamp
50mV/div
Audible Noise
200mV/div
Light Output
1ms/div
Series R=65K
100V/div
Differential Output Waveform across the lamp
50mV/div
Audible Noise
200mV/div
1ms/div
Light Output
10
HV857 Application Note
Circuit 2 Series R=0
100V/div
Differential Output Waveform across the lamp
20mV/div
Audible Noise
200mV/div
Light Output
1ms/div
Series R=55K
100V/div
Differential Output Waveform across the lamp
20mV/div
Audible Noise
200mV/div
1ms/div
Light Output
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
A-weighting filter
Headphones
EL Lamp
Opto-acoustic Probe
NC
EL Driver
10mm
Scaling
+
Scaling Low pass filter NC
DC Supply
Pneumatic Supports
Drawing not to scale
Opto-acoustic probe is battery powered to minimize electrical noise.
12
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=0). Also see Figure 1 and Table 3.
Table 2
Circuit Lamp Size Lamp Brightness ft-lm 3 4 1.3in2 1.7in2 9.38 4.44 4.48 12.0 13.2 7.74 7.84 Cd/m2 32.10 15.2 15.31 41.6 45.3 26.51 26.87 Supply Voltage VDD 3.3V 3.0V VIN 3.3V 3.2V 4.2V 3.2V 4.2V 3.0V 5.0V 12.9mA 7.4mA 5.7mA 23.7mA 20.9mA 8.3mA 17.9mA 180Vp-p 182Vp-p 186Vp-p 168Vp-p 178Vp-p 175Vp-p 184Vp-p 357Hz 160Hz Lx Supply Current Output Voltage Lamp Frequency
5
1.7in2
3.0V
475Hz
6 7
0.93in2 3.1in2
3.0V 5.0V
250Hz 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
Lx Inductor Circuit Value 1 2 3 4 5 6 7 8 9 220H 220H 220H 220H 220H 220H 220H 220H 220H Manufacturer, Part. No. MuRata, LQH32CN221K21 MuRata LQH32CN221K21 MuRata, LQH32CN221K21 MuRata, LQH32CN221K21 MuRata, LQH32CN221K21 MuRata, LQH32CN221K21 MuRata, LQH32CN221K21 MuRata, LQH43MN221K01 MuRata, LQH43MN221K01 RSW-OSC REL-OSC CS Capacitor Value 3.3nF 3.3nF 3.3nF 3.3nF 3.3nF 3.3nF 3.3nF 3.3nF 3.3nF Type NPO NPO NPO NPO NPO NPO NPO NPO NPO
560K 560K 560K 330K 560K 560K 560K 560K 560K
2.0M 2.0M 1.5M 3.3M 1.0M 2.0M 2.0M 2.0M 3.3M
13
HV857 Application Note
LX 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 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.
CS Capacitor Selection:
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
(c)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

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