Features SLEW ENA ELA VDD. 332k ELB RSW MIC M COM REL ENB GND. VIN Li Ion 3V to 4.2V 2.2nF 250V. Low Noise Dual EL Driver

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1 Low Noise Dual 22 V PP Driver With Output Voltage Slew Rate Control General Description The is a low noise dual Electroluminescent () Panel driver used in backlighting applications. The converts a low DC voltage to a high DC voltage using a boost converter and then alternates the high DC voltage across the panels using an H-bridge. The incorporates internal wave-shaping circuitry specifically designed to reduce audible noise emitted by panels. The two panels may be dimmed by applying a PWM signal to the device. The drives two outputs from a single inductor and requires a minimum number of passive components. It features an operating input voltage range of 2.3V to 5.8V, making it suitable for 1-cell Li-ion and 2- or 3-cell alkaline/nicad/nimh battery applications. An external resistor may be used to adjust the output voltage slew rate to reduce audible noise. The features separate oscillators for the boost and H-bridge stages to allow independent control. External resistors set the operating frequencies of each stage allowing the circuit to optimize efficiency and brightness. The is available in a 12 pin 3mmx3mm MLF package, and has an operating junction temperature range of 4 C to +125 C. Features Drives two panels, up to 4 in 2 each at full brightness Independent input control for each of the two panels and allows PWM dimming. 22Vpp regulated AC output waveform 2.3V to 5.8V DC input voltage Wave-shaping circuit to reduce audible noise Adjustable slew rate for audible noise reduction Independently adjustable boost converter and panel frequency Single inductor to power both panels.1ua typical shutdown current 12 pin 3mmx3mm MLF package 4 o C to +125 o C junction temperature range Applications Mobile Phones MP3s/Portable Media Players (PMP) Clocks/ Watches Remote Controls Cordless Phones GPS Devices PDAs Typical Application VIN Li Ion 3V to 4.2V.1µF High Low 332k 1.78M ENA R R SLEW A B COM 5k Lamp A Lamp B High Low High Low ENB CS GND VIN Li Ion 3V to 4.2V 1µF 22µH 2.2nF 25V Low Noise Dual Driver MLF and MicroLead Frame are registered trademark of Amkor Technologies Micrel Inc. 218 Fortune Drive San Jose, CA USA tel +1 (48) fax + 1 (48) October 28 M

2 Ordering Information Part Number YML Package Operating Junction Temp Lead Finish Range 12 pin 3mmx3mm MLF -4 C to +125 C Pb-free / RoHS Compliant Pin Configuration ENA 1 12 SLEW 2 11 A R R ENB GND 3 EP B COM CS Pin Description 12-Pin 3mm 3mm MLF (ML) Top View Pin Number Pin Name Pin Function 1 ENA Panel A Enable Pin: Logic high enables A and logic low disables A output. 2 DC Input Supply Voltage: 2.3V to 5.8V 3 R R pin: Sets internal boost converter switch frequency by connecting an external resistor (R ) to. Connecting the R resistor to GND shuts down the device. 4 R R pin: Sets internal H-bridge driver frequency by connecting an external resistor (R ) to. Connecting the R to GND disables the oscillator. 5 ENB Panel B enable pin: Logic high enables B and logic low disables B output. 6 GND Ground. 7 Switch Node: Drain of internal high-voltage power MOSFET for boost circuit. 8 CS Regulated Boost Output: Connect to the output capacitor of the boost regulator and to the cathode of the diode. 9 COM output: Common output terminal to both A and B. Connect one end of each panel to this pin. 1 B Panel B output: Connect the other end of the panel B to this pin. 11 A Panel A output: Connect the other end of the panel A to this pin. 12 SLEW Optional resistor to set output current drive to control slew rate of load. If left open, the default slew current limit is 5mA. EPad HS Pad Heat Sink Pad. Connect to ground externally. October 28 2 M

3 Absolute Maximum Rating (1) Supply voltage (V DD )..-.5V to 6.5V Output voltage (V CS ) V to 13V Switch Node (V ) V to 13V Enable Voltage (V ENA, V ENB ) V to 6.5V Voltage (V R, V R, V SLEW ) V to 6.5V Ambient Storage Temperature (T S ) C to +15 C ESD Rating (3).... ESD Sensitive Operating Range (2) Supply Voltage (V DD ) V to 5.8V Panel Drive Frequency (f )..1Hz to 15Hz Switching MOSFET Frequency (f )...35kHz to 35kHz Enable Voltage (V ENA, V ENB )...V to V DD Junction Temperature Range (T J ) -4 C to +125 C Package Thermal Impedance θ JA MLF -12L... 6 C/W Electrical Characteristics (4) T A =25 o C, V dd = 3.V unless otherwise noted. Bold values indicate -4 C T J 85 C. Parameter Symbol Condition Min Typ Max Units Supply Voltage Range V DD V Input Supply Current R I =High; V CS =15V; DD A, B, COM, SLEW = Open µa Shutdown Current I SD R =Low; V DD =5.8v.1 1 µa On-resistance Of Switching Transistor R DS (ON) I =1mA, V CS =15V Ω Output voltage Regulation V DD =2.3V to 5.8v V V CS Boost Switching Frequency A, B and COM Drive Frequency Switching Transistor Duty Cycle f Sw f V DD =3.V (R = 1.3MΩ ) V DD =3.V (R = 45kΩ) V DD =3.V (R = 125kΩ) V DD =3.V (R = 1.8 MΩ) A, B = Open Vdd=3.V (R = 712kΩ) A, B = Open khz khz khz Hz Hz D 8 95 % Output Current Drive Limit Programmability I SLEW SLEW = Open ma R SLEW =1kΩ ma Enable Logic Threshold V ENA, V ENB V Enable Logic Hysteresis V HYS mv Enable Input Current I ENA, I ENB.1 1 µa Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 1pF. 4. Specification for packaged product only. October 28 3 M

4 Typical Characteristics ITCHING FREQUENCY (khz) INPUT CURRENT (ma) INPUT CURRENT (ma) Switching Frequency vs Resistor ITCHING RESISTOR (kohm) Input Current vs. Frequency (Dual Lamp) in in in in V IN = 3.6V 15 f = 75kHz FREQUENCY (Hz) Total Input Current vs. Input Voltage f = 2Hz C OUT = 2.2nF f = 68kHz Size = 4in 2 FREQUENCY (Hz) Frequency vs Resistor RESISTOR (MOhm) ITCHING FREQUENCY (khz) Recommended Switching Frequency vs. Total Lamp Size Hz 12 2Hz 1 8 3Hz 6 4Hz 4 2 V IN = 3.V INPUT CURRENT (ma) TOTAL LAMP SIZE (in 2 ) Total Input Current vs. Input Voltage f = 2Hz C OUT = 2.2nF f = 47kHz Size = 6in 2 INPUT CURRENT (ma) INPUT CURRENT (ma) Input Current vs. Frequency (Single Lamp) 6 V IN = 3.6V 5 f = 75kHz 4 in 2 3 in in FREQUENCY (Hz) 1 in 2 Total Input Current vs. Input Voltage f = 2Hz C OUT = 2.2nF f = 1kHz Size = 2in 2 1 f = 122kHz 5 Size = 1in INPUT VOLTAGE (V) 4 f = 45kHz 2 f = 88kHz 4 f = 55kHz 2 f = 2Hz 15 Size = 3in 2 35 Size = 5in 2 C OUT = 2.2nF INPUT VOLTAGE (V) INPUT VOLTAGE (V) INPUT VOLTAGE (V) CS VOLTAGE (V) CS Voltage vs. Input Voltage OUTPUT VOLTAGE (V P-P ) f = 45kHz Output Voltage vs. Input Voltage 4 f = 2Hz C = 2.2nF OUT INPUT VOLTAGE (V) BRIGHTNESS (lux) Brightness vs. Input Voltage 6 Distance = 2 in 4 f = 135kHz 2 f = 225Hz L = 22µH INPUT VOLTAGE (V) October 28 4 M

5 Functional Diagram 22µH CS VCS 2.2nF Output A R Oscillator Driver Driver VREF PGND PGND VCS VSENSE Output Driver COM R Oscillator Driver Logic & PWM Dimming PGND VCS ENA ENB -A Enable -B Enable Output Driver B SLEW Output Wave-Shaping PGND PGND GND GND Figure 1. Block Diagram October 28 5 M

6 Functional Description Overview The is a high-voltage dual output driver with a peak-to-peak AC output voltage of 22V capable of driving two 4 in 2 panels. The drives panels by converting a low DC input voltage to a DC high output voltage using the boost regulator circuit and then alternating the high DC voltage across the panel using an H-Bridge. Input supply current for the is typically 152µA. The high voltage driver has two internal oscillators to control the boost switching frequency and the H-bridge driver frequency. Both of the internal oscillators frequencies can be individually programmed through external resistors to maximize efficiency and brightness of the panel. The can be dimmed using a PWM signal applied to the R pin with an external capacitor. An external resistor can be used to adjust the internal wave shaping circuit to reduce audible noise. Regulation Referring to Figure 1, power is initially applied to V DD. When the internal feedback voltage is less than the reference voltage, the internal comparator enables switching in the boost circuit. When the boost regulator is switching, current flows through the inductor into the switch. The switching MOSFET will typically turn on for 9% of the switching period. During the on-time, energy is stored in the inductor. When the switching MOSFET turns off, current flowing into the inductor forces the voltage across the inductor to reverse polarity. The voltage across the inductor rises until the external diode conducts and clamps the voltage at V OUT + V D1. The energy in the inductor is then discharged into the C OUT capacitor. The internal comparator continues to turn the switching MOSFET on and off until the internal feedback voltage is above the reference voltage. Once the internal feedback voltage is above the reference voltage, the internal comparator disables switching. The control circuit will continue to turn the MOSFET s on and off to maintain a constant DC voltage at the CS pin. When the Driver is enabled, A and B will switch in opposite states with COM to achieve a 22V peak-to-peak AC output signal needed to drive the two panels. R and. The switching frequency increases as the resistor value decreases. In general, the lower the switching frequency, the greater the input current is drawn to deliver more power to the output. Lowering the switching frequency can be used to drive larger panels. However, the switching frequency should not be so low as to allow the voltage at the switch node or the CS pin to exceed the absolute maximum voltage of those pins. For resistor value selections, see the Typical Characteristics: Switching Frequency vs. Resistor graph on Page 4 or use the equation below. The switching frequency range is 35kHz to 35kHz, with an accuracy of ±2%. 46 f (khz) = R ( MΩ) Frequency The panel frequency is controlled via an external resistor (R ) connected between R and. The panel frequency increases as the resistor value decreases. In general, as the panel frequency increases, the amount of current drawn from the battery will increase. The panel brightness is dependent upon its frequency. For resistor value selections, see the Typical Characteristics: Frequency vs. Resistor graph on Page 4 or use the equation below. The panel frequency range is 1Hz to 15Hz, with an accuracy of ±2%. ( Hz) f = 425 R ( MΩ) Enable Function There are a few different ways to enable and disable the. The boost regulator may be disabled by pulling the R resistor to ground. This turns off both the panels by cutting power to the device completely. The panels can also be turned off by pulling the R resistor to ground. Although this turns off the H-Bridge and the panels, the boost regulator will continue regulate. For individual panel control, the ENA and ENB pins can be used to enable A and B, respectively. Pulling ENA or ENB high or low will turn A and B panels on or off. Switching Frequency The switching frequency of the converter is controlled via an external resistor (R ) between October 28 6 M

7 Figure 2. 15Hz Output Waveform PWM Dimming The may be dimmed by adding a shunt capacitor (C PWM ) to the R pin, shown in Figure 5. The duty cycle of the PWM signal changes the frequency of the panel, thereby changing its brightness. Increasing the PWM duty cycle increases the frequency to a maximum set by R (Duty Cycle = 1%). Decreasing the PWM duty cycle decreases the frequency. The PWM duty cycle should not be lowered to a level that may cause the frequency to be lower than 1Hz, since frequencies lower than 1Hz may cause the panel to flicker. The frequency of the PWM signal can range from 5Hz to 5kHz. The peak voltage of the PWM signal should be equal to. V PWM 1kHz R C PWM.1µF R pin Figure 5. PWM Dimming Circuit Figure 3. 25Hz Output Waveform Slew Resistor The is designed to reduce audible noise in panels by the use of the internal wave-shaping circuit. To further reduce audible noise, a Slew Resistor (R SLEW ) can be added to limit the rate of change of the driver output voltage by limiting the output current. A slower rate of change in voltage across the panel creates less physical distortion in the material and therefore reduces the amount of audible noise. The lower the I SLEW, the slower the output voltage across the panel will change. If R SLEW is not used, the I SLEW is by default 5mA, equivalent to using a 22kΩ for R SLEW. Figure 4. 35Hz Output Waveform R SLEW Open 125kΩ 22kΩ 1kΩ I SLEW 5mA 1mA 5mA 1mA Table 1. Slew Resistor Setting October 28 7 M

8 Application Information The is designed to use an inductance with a value between 1µH to 33µH. Choosing the right inductor is always a balance of size, inductance, efficiency, current rating and cost. A TDK (VLS412T-221M) 22µH inductor is recommended based on size, efficiency and current rating. Generally, the lower the inductance, the more current the inductor can handle. Lowering the inductance allows the boost regulator to draw more input current to deliver more energy every switching cycle. As a result, a lower inductance may be used to drive larger panels or brighten similar sized panels. However, caution is required as using a low inductance with a low switching frequency may cause the voltage at the switch node and the CS pin to exceed the absolute maximum rating. If the application uses a low input voltage (2.3 to 3V), a lower value inductor, such as 1µH, may be used in order to drive the panel at maximum brightness. Diode The diode must have a high reverse voltage (15V), since the output voltage at the CS pin can reach up to 13V. A fast switching diode with lower forward voltage and higher reverse voltage (15V), such as BAV2WS/BAS2W, can be used to enhance efficiency. Output Capacitor Low ESR capacitors should be used at the regulated boost output (CS pin), to minimize the switching output ripple voltage. The larger the output capacitance, the lower the output ripple at the CS pin. The reduced output ripple at the CS pin along with a low ESR capacitor improves the efficiency of the circuit. Selection of the capacitor value depends upon the peak inductor current, inductor size, and the load. The is designed for use with an output capacitance as low as 2.2nF. For minimum audible noise, the use of a CG/NPO dielectric output capacitor is recommended. TDK and AVX offer CG/NPO dielectric capacitors in capacitances up to 2.7nF capacitance at 2V to 25V voltage rating in 85 size. Panel Terminals (A, B, COM) The two panels are connected from A to COM and B to COM. The A and B terminals are in phase with each other, while the COM is out of phase with both A and B. Since A and COM are out of phase, the high voltage generated by the boost regulator is alternated across A and COM by the H-Bridge. The frequency of each cycle is determined by R. The alternating 22V peak-topeak causes the panel to emit light. Similarly, the B and COM are also out of phase and allows a second panel to be driven at the same time. Both panels may operate independently from each other and do not have to be the same size. For component selection, Table 2 lists recommended values for various panel sizes up to a total of 8in 2 (For example, two 4in 2 panels). Driving overly large panels will result in a dimmer display, but will not cause damage to the device. October 28 8 M

9 Application Circuit VIN Li Ion 3V to 4.2V C1.1µF High Low R 332k R 1.78M ENA R R SLEW A B COM RSLEW 5k Lamp A Lamp B High Low High Low ENB CS GND VIN Li Ion 3V to 4.2V C2 1µF L1 22µH C3 2.2nF 25V Figure 6: Typical Li-Ion Powered Circuit Note: Table 2 applies to circuit shown in Figure 6. Total Panel Area (inch 2 ) Capacitance (nf) Panel Frequency (Hz) R (MΩ) R (kω) f (khz) R (kω) f (khz) R (kω) f (khz) R (kω) f (khz) R (kω) f (khz) R (kω) f (khz) R (kω) f (khz) R (kω) 1 f (khz) 45 Table 2: Recommended R & R Values For Total Panel Sizes October 28 9 M

10 Bill of Materials Item Part Number Manufacturer Description Qty C1 C168X7R1A13K TDK (1).1µF Ceramic Capacitor, 1V, X7R, Size 63 1 C2 C168X5RJ16K TDK (1) 1 µf Ceramic Capacitor, 6.3V, X5R, Size 63 1 C3 C212CG2E2222J TDK (1).22µF Ceramic Capacitor, 25V, CG, Size 85 1 L1 VLS412T-221M TDK (1) 22µH, 21mA I SAT. (4mmx4mmx1.2mm) 1 D1 BAS2-V-GS18 Vishay (2) 2V/2mA Hi-Voltage Switching Diode 1 R1 or R CRCW633323FKEYE3 Vishay (2) 332kΩ, 1%, 1/16W, Size 63 1 R2 or R CRCW631784FKEYE3 Vishay (2) 1.78MΩ, 1%, 1/16W, Size 63 1 R SLEW U1 YML Micrel (3) Low Noise Dual 22Vp-p Driver with Output Slew Control 1 Optional Notes: 1. TDK: 2. Vishay: 3. Micrel, Inc.: October 28 1 M

11 Layout Recommendation Top Layer Bottom Layer October M

12 Package Information 12-Pin 3mm x 3mm MLF (ML) MICR, INC. 218 FORTUNE DRIVE SAN JOSE, CA USA T +1 (48) FAX +1 (48) WEB The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. 28 Micrel, Incorporated. October M