HV857 Low Noise, High Voltage EL Lamp Driver IC Features 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/GND. Patented audible noise reduction Patented lamp aging compensation 190 VPP 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 ► Available in MSOP-8 and DFN-8 packages 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 RELOsc pin and VDD pin. An external inductor is connected between the LX and VDD pins or VIN for split supply applications. A 0.0030.1µF capacitor is connected between CS and ground. The EL lamp is connected between VA and VB. Applications ► ► ► ► ► LCD backlighting Mobile Cellular Phone PDAs Handheld wireless communication products Global Positioning Systems (GPS) 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. Typical Application Circuit Enable Signal ON = VDD OFF = 0 + VDD _ CDD 1 VDD VA 8 2 RSW-Osc VB 7 REL-Osc CS 6 LX 5 RSW EL Lamp 3 REL D 4 GND VIN + _ CIN HV857MG LX CS HV857 Ordering Information Package Options Device 8-Lead DFN (K7) 8-Lead MSOP (MG) HV857K7-G HV857MG-G HV857 -G indicates package is RoHS compliant (‘Green’) Absolute Maximum Ratings Pin Configuration Parameter Value Supply Voltage, VDD Top View -0.5V to 6.5V Operating Temperature Storage Temperature -65°C to +150°C RSW-Osc 2 1.6W REL-Osc 3 300mW GND 4 DFN-8 Power Dissipation MSOP-8 Power Dissipation 7 VB MSOP-8 6 HV857MG 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. VDD 1 RSW-Osc 2 Thermal Resistance Package θja DFN-8 60OC/W CS 5 LX -0.5 to +120V Output voltage, VCS MSOP-8 8 VA VDD 1 -40°C to +85°C 8 VA 7 VB DFN-8 REL-Osc 3 6 CS GND 4 5 LX HV857K7 Pads are at the bottom of the package Exposed center pad is at ground potential 330OC/W Mounted on FR4 board, 25mm x 25mm x 1.57mm Recommended Operating Conditions Symbol Parameter Min Typ Max Units Conditions VDD Supply voltage 1.8 - 5.0 V --- fEL Operating drive frequency - - 1 kHz --- TA Operating temperature -40 - +85 O C --- Enable/Disable Function Table Symbol Parameter Min Typ Max Units EN-L EN-H Conditions Logic input low voltage 0 - 0.2 V VDD = 1.8V to 5.0V Logic input high voltage VDD - 0.2 - VDD V VDD = 1.8V to 5.0V Electrical Characteristics DC Characteristics (Over recommended operating conditions unless otherwise specified, T =25°C) A Symbol Parameter Min Typ Max Units - - 6.0 Ω RDS(ON) On-resistance of switching transistor VCS Max. output regulation voltage 85 95 105 V VDD=1.8V to 5.0V 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 2 Conditions I = 100mA HV857 Electrical Characteristics (cont.) Symbol Parameter Min Typ Max Units IDD Conditions 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 205 240 275 Hz See Figure 1 fSW Switching transistor frequency - 80 - kHz See Figure 1 D Switching transistor duty cycle - 88 - % See Figure 1 * The inductor used is a 220µH Murata inductor, max DC resistance of 8.4Ω, part # LQH32CN221K21. Block Diagram LX VDD CS Switch Osc RSW-Osc Q VA GND VSENSE + Disable C Q VREF _ High Voltage Level Translator VDD Q EL Osc REL-Osc VB Q Figure 1: Typical Application/ Test Circuit ON = VDD Enable Signal OFF = 0V + 2.0kΩ 560kΩ 0.1µF VDD - 1 VDD VA 8 2 RSW-Osc VB 7 3 REL-Osc CS 6 4 GND LX 5 Equivalent to 3.0in2 lamp 10nF BAS21 2.0MΩ HV857MG + 220µH* 4.7µF VIN * Murata Inductor LQH32CN221K21 3 3.3nF, 100V HV857 Typical Performance Device Lamp Size VDD = VIN IIN VCS fEL Brightness HV857MG-G 3.0in2 3.3V 20.0mA 84V 240Hz 6.0ft-lm Typical Performance Curves for Figure 1 (EL Lamp = 3.0in , V 2 DD = 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 VIN (V) Brightness vs VIN 5.5 IIN vs VCS 24 7 6 5 4 3 2 1 1.5 lIN (mA) 22 20 18 16 2.5 3.5 4.5 14 55 5.5 65 75 85 95 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) 60 Brightness 4 50 3 40 Iin 30 2 lIN 20 1 10 0 0 100 150 200 250 300 350 400 Inductor Value (µH) 4 450 500 550 600 Brightness (ft-lm) VCS (V) 95 HV857 External Component Description External Component Description Diode Fast reverse recovery diode, BAS21 diode or equivalent. CS Capacitor 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 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. REL Resistor A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the REL resistor by a factor of 2 will increase the lamp frequency by a factor of 2. fEL = RSW Resistor REL 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. fSW = LX Inductor (2MΩ)(240Hz) (560kΩ)(80kHz) RSW 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. A 220µH Murata (LQH32CN221) inductor with 8.4Ω series DC resistance is typically recommended. For inductors with the same inductance value, but with lower series DC resistance, lower RSW resistor 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, 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. The control signal has to track the VDD supply. 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 Enable Signal OFF = 0V Regulated Voltage = VDD RSW CDD 1 VDD VA 8 2 RSW-Osc VB 7 3 REL-Osc CS 6 4 GND LX 5 EL Lamp D REL HV857MG + CIN VIN LX CS - Audible Noise Reduction This section describes a method (patented) developed at Supertex to reduce the audible noise emitted by the EL lamps used in application sensitive to audible noise. Figure 3 shows a general circuit schematic that uses the resistor, RSER, connected in series with the EL lamp. Figure 3: Typical Application Circuit for Audible Noise Reduction Enable ON = VDD OFF = 0V RSER + VDD CDD RSW 1 VDD VA 8 2 RSW-Osc VB 7 3 REL-Osc CS 6 4 GND LX 5 EL Lamp - D REL HV857MG + VIN CIN - 6 LX CS HV857 formance of the Supertex EL drivers, age compensation (patented). This addresses a very important issue, EL lamp life that most mobile phone manufacturers are concerned about. Minimization of EL Lamp Audible Noise The EL lamp, when lit, emits an audible noise. This is due to EL lamp construction and it 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. Effect of Series Resistor on EL Lamp Audible Noise and Brightness As EL lamp ages, its brightness is reduced and its capacitance is diminished. By using the RC model to reduce the audible noise emitted by the 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 the EL lamp’s half-life (half the original brightness). Increasing the value of the series resistor with the lamp will reduce the EL lamp audible noise 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. 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 C is the capacitance of the EL lamp, and R is the external resistor, RSER, connected in series with the EL 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. 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 have another effect on the over all per- 7 HV857 8-Lead DFN Package Outline (K7) 3x3mm body, 0.80mm height (max), 0.65mm pitch D2 D 8 8 E E2 Note 1 (Index Area D/2 x E/2) Note 1 (Index Area D/2 x E/2) 1 1 View B Top View Bottom View Note 3 θ A A3 e b L Seating Plane L1 Note 2 A1 View B Side View Notes: 1. Details of Pin 1 identifier are optional, but must be located within the indicated area. The Pin 1 identifier may be either a mold, or an embedded metal or marked feature. 2. Depending on the method of manufacturing, a maximum of 0.15mm pullback (L1) may be present. 3. The inner tip of the lead may be either rounded or square. Symbol MIN Dimension (mm) A A1 0.70 0.00 NOM 0.75 0.02 MAX 0.80 0.05 A3 0.20 REF b D D2 E E2 0.25 2.85 1.60 2.85 1.35 0.30 3.00 - 3.00 - 0.35 3.15 2.50 3.15 1.75 JEDEC Registration MO-229, Variation WEEC-2, Issue C, Aug. 2003. Drawings not to scale 8 e 0.65 BSC L L1 θ 0.30 - 0O 0.40 - - 0.50 0.15 14O HV857 8-Lead MSOP Package Outline (MG) 3x3mm body, 1.10mm height (max), 0.65mm pitch D θ1 (x4) 8 E E1 L2 Note 1 (Index Area D1/2 x E1/2) L 1 Top View View B A A Seating Plane θ L1 Gauge Plane View B A2 A Seating Plane b e A1 View A-A Side View Note 1: A Pin 1 identifier must be located in the index area indicated. The Pin 1 identifier may be either a mold, or an embedded metal or marked feature. Symbol Dimension (mm) MIN NOM MAX A 0.75 1.10 A1 0.00 0.15 A2 0.75 0.85 0.95 b 0.22 0.38 D 2.80 3.00 3.20 E 4.65 4.90 5.15 E1 e 2.80 3.00 3.20 L L1 L2 0.40 0.65 BSC 0.60 0.80 θ 0 0.95 REF 0.25 BSC O 8 O θ1 5O 15O JEDEC Registration MO-187, Variation AA, Issue E, Dec. 2004. Drawings not to scale. (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to http://www.supertex.com/packaging.html.) Doc.# DSFP-HV857 NR110806 9