LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET KEY FEATURES DESCRIPTION equal to 1.6V with sustained operation as low as 1.1V. The maximum LED drive current is easily programmed using one external current sense resistor in series with the LEDs. In this configuration, LED current provides a feedback signal to the FB pin, maintaining constant current regardless of varying LED forward voltage (VF). Depending on the MOSFET selected, the LX1744 is capable of achieving an LED drive in excess of 1.0W. The LX1744 provides simple dynamic adjustment of the LED drive current (0% to 100% full range dimming) and the LCD Bias output voltage (up to ±15% typ) through separate IC interfaces. Each interface has an internal RC filter allowing designers to make these adjustments via a direct PWM input signal or an analog reference signal. Further, any PWM amplitude is easily accommodated using a single external resistor. The LX1744 is available in the 14-Pin TSSOP, and the miniature 16-Pin MLP requiring minimal PCB area. > 90% Maximum Efficiency Low Quiescent Supply Current Externally Programmable Peak Inductor Current Limit for Maximum Efficiency Logic Controlled Shutdown < 1µA Shutdown Current Dynamic Output LED Current and LCD Bias Voltage Adjustment via Analog Reference or Direct PWM Input 14-Pin TSSOP or 16-Pin MLPQ Package WWW . Microsemi .C OM The LX1744 is a compact high efficiency step-up boost regulator for driving white or color LEDs in LCD lighting applications while supplying the necessary LCD bias voltage with an additional integrated boost converter. Designed for maximum efficiency and featuring a psuedo-hysteretic PFM topology (that decreases output voltage ripple), the LX1744 minimizes system cost and condenses layout area making it ideal for PDA, smart-phone, and digital camera applications. While the LCD Bias generation is implemented using an internal N-Channel MOSFET, the LED driver utilizes an external N-Channel MOSFET in order to maintain maximum efficiency along with flexible power requirements. The LX1744’s control circuitry is optimized for portable systems with a shutdown current of less than 1µA. The input voltage range of 1.6V to 6.0V allows for a wide selection of system battery voltages and start-up is guaranteed at a VIN APPLICATIONS Pagers Smart Phones PDAs Handheld Computers General LCD Bias Applications LED Driver IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT ILED = 20mA to 0mA L1 VBAT = 1.6V to 6.0V 47µH 1206 Case Size - VLCD C1 4.7µF DRV IN SRC VLCD1 = VIN to 25V SW1 OVP LFB FB1 CS LX1744 LSHDN SW2 ON OFF RSET 15Ω BRT REF FB2 GND VLCD2 = VIN to 25V SHDN2 SHDN1 ON OFF ADJ1 ADJ2 ON OFF LX1744 Evaluation Board LX1744 PACKAGE ORDER INFO TA (°C) -40 to 85 PW Plastic TSSOP 14-Pin LQ Plastic MLP-Q 16-Pin RoHS Compliant / Pb-free Transition DC: 0442 RoHS Compliant / Pb-free Transition DC: 0430 LX1744CPW LX1744CLQ Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1744CLQ-TR) Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET PACKAGE PIN OUT Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal. 14 GND 2 13 SRC FB 3 12 DRV ADJ 4 11 CS REF 5 10 OVP IN 6 9 LFB LSHDN 7 8 BRT PW PACKAGE GND SRC 16 15 14 13 SW 1 12 DRV SHDN1 2 11 CS FB 3 10 OVP ADJ 4 9 LFB 6 7 8 BRT 31°C/W 5 LSHDN Plastic MLPQ 16-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA GND (Top View) IN LQ 1 REF THERMAL DATA SW SHDN N.C. Supply Input Voltage ...........................................................................-0.3V to 7V Feedback Input Voltage (VFB, VLFB).......................................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN , V LSHDN )) ...........................-0.3V to VIN + 0.3V PWM Input Amplitude (ADJ, BRT).......................................-0.3V to VIN + 0.3V Analog Adjust Input Voltage (VADJ, VBRT) .............................-0.3V to VIN + 0.3V SRC Input Current ................................................................................ 800mARMS Operating Temperature Range .........................................................-40°C to 85°C Maximum Operating Junction Temperature ................................................ 150°C Storage Temperature Range...........................................................-65°C to 150°C RoHS Peak Package Solder Reflow Temperature (40 second maximum exposure) ..................................................... 260°C (+0, -5) WWW . Microsemi .C OM ABSOLUTE MAXIMUM RATINGS LQ PACKAGE (Bottom View) (“N.C.” = No Internal Connection) PW Plastic TSSOP 14-Pin RoHS / Pb-free 100% Matte Tin Lead Finish THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 90°C/W Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. PACKAGE DATA Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET FUNCTIONAL PIN DESCRIPTION Description IN Unregulated IC Supply Voltage Input – Input range from +1.6V to 6.0V. Bypass with a 1µF or greater capacitor for operation below 2.0V. DRV LED MOSFET Gate Driver – Connects to an external N-Channel MOSFET. SRC LED MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source. OVP Over Voltage Programming Pin – Connects to a resistor divider between the output load and GND to set the maximum output voltage. OVP has a voltage threshold of 1.2V LFB LED Current Feedback Input – Connects to a current sense resistor between the LED output load and GND to set the LED drive current. GND Common terminal for ground reference. BRT LED Dimming Signal Input – Provides the internal reference, via an internal filter and gain resistor, allowing for a dynamic output LED current adjustment that corresponds to the PWM input signal duty cycle. Either a PWM signal or analog voltage can be used. The actual BRT pin voltage range is from VIN to GND. Minimize the current sense resistor power dissipation by selecting a range for VBRT = 0.0V to 0.5V. REF Buffered Reference Output – Connected to the internal bandgap reference voltage of 1.2V. SW LCD Bias Inductor Switch Connection – Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. FB Feedback Input – Connect to a resistive divider network between the output and GND to set the output voltage between VCC (IN) and 25V. The feedback threshold is 1.29V. ADJ LCD Bias Adjustment PWM Signal Input – Connect to an RC filter allowing for dynamic output voltage adjustment >±15%, corresponding to a varying duty cycle. Either a PWM signal or analog voltage can be used. The ADJ input voltage range is from 0.9V to VIN DC. The ADJx pin should be connected to ground when the internal reference is used. LSHDN LED Driver Active-Low Shutdown Input – A logic low shuts down the LED driver circuitry and reduces the supply current by 60µA (Typ). Pull LSHDN high for normal operation. SHDNx LCD Bias Active-Low Shutdown Input – A logic low shuts down the LCD Bias circuitry and reduces the supply current by 60µA (Typ). Pull SHDNx high for normal operation. CS WWW . Microsemi .C OM Name Current-Sense Amplifier Input – Connecting a resistor between CS and GND sets the peak inductor current limit. PACKAGE DATA Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET ELECTRICAL CHARACTERISTICS Parameter ` LFB Input Bias Current BRT Input Voltage Range BRT Input Bias Current LED Driver Shutdown Input Bias Current LED Driver Shutdown High Input Voltage LED Driver Shutdown Low Input Voltage Current Sense Bias Current Efficiency DRV Sink/Source Current DRV On-Resistance Maximum Switch On-Time Minimum Switch Off-Time Switch Peak Current OVP Threshold Voltage Min LX1744 Typ Max Units LCD BIAS Output Voltage Range FB Threshold Voltage FB Input Current LCD Bias Shutdown Input Bias Current LCD Bias Shutdown High Input Voltage LCD Bias Shutdown Low Input Voltage Peak Inductor Current Limit Internal NFET On-resistance Switch Pin Leakage Current Efficiency Switch On-Time Switch Off-Time ADJ Input Voltage Range ADJ Input Bias Current ENTIRE REGULATOR Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Reference Voltage Quiescent Current Copyright © 2000 Rev. 1.1b, 2005-03-01 BRT = VREF 95 5 -100 0.0 0 I SHDN1 0.0V ≤ LSHDN ≤ VIN -100 V SHDN1 VIN = 2V V SHDN1 VIN = 2V VLFB VBRT = 100mV VBRT = 20mV VLFB = 100mV VBRT ICS η tON tOFF ILOAD = 2mA VIN = 5V, DRV = 3V VCC = 5V VFB = 1V VFB = 1V RCS = 0Ω RCS = 2kΩ 100 20 100 1.6 85 200 4 90 100 12 VOVP 1.15 VOUT VFB 1.172 1.196 VFB = 1.4V I SHDN SHDN = GND V SHDN VIN = 2V V SHDN VIN = 2V ILIM RDS(ON) ILEAK η tON tOFF VADJ IADJ ISW = 10mA, TA = 25°C, VIN = 5V VSW = 25V ILOAD = 2mA VFB = 1V VFB = 1V VIN V 15 ∞ 410 µA % mA Ω µS nS mA 1.26 V 25 1.220 200 V V nA 100 nA 0.4 195 1.1 ∞ 400 1.5 1 6.0 1.6 V V 1 150 0.9 0.3 1.6 -2 IQ 1.187 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 1.21 120 60 60 0.35 V mA Ω µA % µs Ns V µA 85 VFB = 0.3V, VLFB < VBRT – 0.1V VFB = 0.3V, VLFB < VBRT – 0.1V, V LSHDN < 0.4V VFB = 0.3V, VLFB < VBRT – 0.1V, V SHDN < 0.4V V LSHDN < 0.4V, V SHDN < 0.4V nA V TA = +25°C VREF nA V nA 0.4 1.6 VADJ = 1.5V mV V 300 170 210 1.21V IPK 115 35 100 VIN 60 mV/°C 1.236 200 135 135 0.5 V µA Page 4 ELECTRICALS ` Test Conditions 70°C except where LED DRIVER LFB Threshold Voltage ` Symbol ≤ WWW . Microsemi .C OM Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA otherwise noted and the following test conditions: VIN = 3V, ILED = 20mA, SHDN1 = VIN, SHDN2 = VIN LX1744 I N T E G R A T E D P R O D U C T S Dual Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET SIMPLIFIED BLOCK DIAGRAM WWW . Microsemi .C OM LFB Control Logic Driver DRV SRC Reference Logic BRT 50pF GND 2.5MΩ 4µA CS LSHDN Shutdown Logic IN SHDN OVP FB Control Logic REF SW Driver Reference Logic ADJ 50pF 2.5MΩ 4µA Figure – Simplified Block Diagram BLOCK DIAGRAM Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET APPLICATION CIRCUITS WWW . Microsemi .C OM ILED = 20mA to 0mA L1 VBAT = 1.6V to 6.0V 47µH 1206 Case Size - VLCD C1 4.7µF DRV IN SRC SW OVP VLCD = VIN to 25V LFB CS LX1744 LSHDN FB ON OFF ON OFF RSET 15Ω BRT SHDN REF ADJ GND Figure 1 – LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via PWM Input ILED = 20mA to 0mA L1 VBAT = 1.6V to 6.0V 47µH 1206 Case Size - VLCD C1 4.7µF DRV IN SRC SW OVP VLCD = VIN to 25V LFB CS LX1744 LSHDN FB ON OFF ON OFF BRT SHDN RSET 15Ω REF ADJ GND Note: The component values shown are only examples for a working system. Actual values will vary greatly depending on desired parameters, efficiency, and layout constraints. Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 APPLICATIONS Figure 2 – LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via Analog Voltage Input LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET APPLICATION NOTE LCD BIAS – OUTPUT VOLTAGE PROGRAMMING Selecting the appropriate values for LCD Bias output voltage divider (Figure 3), connected to the feedback pin, programs the output voltage. Using a value between 40kΩ and 75kΩ for R2 works well in most applications. R1 can be determined by the following equation (where VREF = 1.19V nominal): R1 = R 2 VOUT - VREF VREF eq. 1 LCD BIAS – OUTPUT VOLTAGE ADJUSTMENT The LX1744 allows for the dynamic adjustment of the of the voltage output via an adjustment pin (ADJ). Any voltage applied to the adjustment pin works in conjunction with the internal reference logic. The LX1744 will automatically utilize the internal reference when no signal is detected or when the adjustment signal voltage is below approximately 0.6V. This adjustment pin includes an internal 50pF capacitor to ground (Figure 4) that works with an external resistor to create a low-pass filter. This allows a direct PWM (fPWM ≥ 100KHz) signal input to be used for the voltage adjustment signal. (Consequently a DC bias signal can also be used). LX1744 Reference Logic 50pF ADJ WWW . Microsemi .C OM FUNCTIONAL DESCRIPTION The LX1744 is a dual output Pulse Frequency Modulated (PFM) boost converter that is optimized for large step-up voltage applications like LCD biasing and LED drive. Operating in a pseudo-hysteretic mode with a fixed switch “off time” of 300ns, converter switching is enabled when the feedback voltage (VFB) falls below the bandgap reference voltage or the ADJ pin voltage managed by the reference logic block (see Block Diagram). When this occurs, the feedback comparator activates the switching logic, pulling the gate of the power MOSFET high. This in turn connects the boost inductor to ground causing current to flow building up the energy stored in the inductor. The output remains “on”, until the inductor current ramps up to the peak current level set either by the CS pin programming resistor (RCS) in the case of the LED driver or by an internal reference threshold for the LCD bias output. During this switch cycle, the load is powered from energy stored in the output capacitor. Once the peak inductor current value is achieved, the driver output is turned off, for the fixed offtime period of 300ns, allowing a portion of the energy stored in the inductor to be delivered to the load causing output voltage to rise at the input to the feedback circuit. If the voltage at the feedback pin is less than the internal reference at the end of the off-time period, the output switches the power MOSFET “on” and the inductor charging cycle repeats until the feedback pin voltage is greater than the internal reference. Typical converter switching behavior is shown in Figure 12. RADJ_1 2.5MΩ Figure 4 – LCD Bias Adjustment Input Different PWM signal levels can be accommodated by selecting a value for RPWM such that the filtered VADJ value is equal to the reference voltage (eq. 2) ⎛ ⎞ 2.5MΩ ⎟ VADJ = VPWM ⋅ Duty Cycle ⋅ ⎜ ⎜ 2.5MΩ + R ⎟ PWM _ 1 ⎠ ⎝ VBAT = 1.6V to 6.0V eq. 2 LX1744 SW LX1744 FB RADJ_1 ADJ R1 CADJ R2 Figure 3 – LCD Bias Output Voltage Copyright © 2000 Rev. 1.1b, 2005-03-01 RADJ_2 Figure 5 – LCD Bias Adjustment Input Filter Ideally the resultant ripple on the ADJ pin should be approximately 1% or 40dB down from the nominal reference. When using a PWM with a frequency that is Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 APPLICATIONS VOUT LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET APPLICATION NOTE CPWM = 50 π ⋅ fPWM ⋅ RPWM _ 1 eq. 3 where eq. 4 RPWM _ 1 << 2.5MΩ LED DRIVER – OUTPUT CURRENT PROGRAMMING Maximum LED current is easily programmed by choosing the appropriate value for RLED (Figure 6). It is recommended that a minimum value of 15Ω be used for this resistor in order to prevent noise coupling issues on the feedback line. Although, alternate values can be calculated using the following equation: RLED = VBRT(MAX) eq. 5 ILED(MAX) D1 L1 300mV (VBRT) be used in order to minimize dissipative losses in the LED current sense resistor (RLED). Like the LCD bias adjustment (ADJ) pin, the BRT pin is connected to an internal 50pF capacitor to ground that works with an external resistor to create a low-pass filter, allowing the BRT pin to driven directly by a PWM signal whose frequency is greater than 100kHz. When this pin is driven by a PWM signal whose frequency is less than 100kHz, an external filter capacitor is needed. This capacitor is selected such that the ripple component of the resultant voltage on the BRT pin is less than 10% of the nominal input voltage. For PWM frequencies greater than 100kHz, the external BRT input resistor is calculated using the following equation. ⎛ V (DCMAX ) − VBRT(MAX) ⎞ ⎟ RBRT _ 1 = 2.5MΩ ⋅ ⎜ PWM ⎜ ⎟ VBRT(MAX) ⎝ ⎠ WWW . Microsemi .C OM less than 100kHz, an external filter capacitor will be needed (Figure 5). The value of CPWM is easily calculated based on the PWM frequency and RPWM_1 using the following equation. eq. 6 where VBRT is the selected maximum LED current sense feedback threshold. For PWM frequencies less than 100kHz, the external BRT input resistors and filter capacitor (Figure 4) are calculated using the following equations. VBAT = 1.6V to 6.0V ROVP_1 C1 4.7µF ⎛ V (DCMAX ) − VBRT(MAX) ⎞ ⎟ RBRT _ 1 = RBRT _ 2 ⋅ ⎜ PWM ⎜ ⎟ VBRT(MAX) ⎝ ⎠ DRV SRC ROVP_2 eq. 7 OVP where RBRT_2 is selected and VBRT(MAX) is the selected maximum LED current sense feedback threshold. LFB LX1744 RCS CS RBRT_1 RLED 15Ω CBRT = BRT CBRT RBRT_2 ⎛R + RBRT _ 2 ⎞ ⎟ ⋅ ⎜ BRT _ 1 ⎜R ⎟ ⎝ BRT _ 1 ⋅ RBRT _ 2 ⎠ eq. 8 where VRIPPLE is selected to be 10% of VBRT, and fPWM is the PWM signal frequency. Figure 6 – LED Current Programming DIODE SELECTION A Schottky diode is recommended for most applications (e.g. Microsemi UPS5817). The low forward voltage drop and fast recovery time associated with this device supports the switching demands associated with this circuit topology. The designer is encouraged to consider the diode’s average and peak current ratings with respect to the application’s output and peak inductor current requirements. Further, the diode’s reverse breakdown voltage characteristic must be capable of withstanding a Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 APPLICATIONS LED DRIVER – LED BRIGHTNESS ADJUSTMENT The LX1744 features a full range dimming LED driver. LED current regulation is accomplished by using the applied BRT pin voltage as the LED current reference. This reference voltage, in conjunction with the LED current setting resistor (RLED), sets the LED output current. Dimming can be accomplished in one of two ways: by applying a variable DC voltage, or by varying the duty cycle (DC) of a PWM control signal, directly to the BRT pin. It is recommended that a maximum signal voltage of Copyright © 2000 Rev. 1.1b, 2005-03-01 5 π ⋅ fPWM LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET APPLICATION NOTE OVER VOLTAGE PROTECTION PROGRAMMING Since the output of the LED Driver is a current mode configuration, it may be desirable to protect the output from an over-voltage condition in the event the load is removed or not present. The LX1744 includes an over voltage monitor that is easily programmed with two external resistors (Figure 6). This feature eliminates the need for a Zener Diode clamp on the output. Programming is accomplished by first selecting ROVP_2 and then calculating ROVP_1 using the following equation. R OVP _ 1 = ROVP _ 2 VOVP - VREF VREF POUT η ⋅ VIN eq. 10 where POUT is the total output power, η is the expected conversion efficiency, and VIN is the input voltage. From the calculated desired IPK an RCS resistance value Copyright © 2000 Rev. 1.1b, 2005-03-01 eq. 11 1000 800 600 400 200 0 0 5 10 15 20 RCS (kΩ ) Figure 7 – Peak Current Programming Resistor This graph characterizes the relationship between peak inductor current, the inductance value, and the RCS programming resistor. INDUCTOR SELECTION An inductor value of 47µH has been show to yield very good results. Choosing a lower value emphasizes peak current overshoot, effectively raises the switching frequency, and increases the dissipative losses due to increased currents. OUTPUT CAPACITOR SELECTION Output voltage ripple is a function of the several parameters: inductor value, output capacitance value, peak switch current, load current, input voltage, and the output voltage. All of these factors can be summarized by the following equation: ⎛ L ⋅ I ⋅ I ⎞⎛ ⎞ eq. 1 IPK ⋅ IOUT ⎟⎟ + VRIPPLE ≅ ⎜⎜ PK OUT ⎟⎟⎜⎜ ⎝ COUT ⎠⎝ VIN − ( VSW + VL ) VOUT + VF − VIN ⎠ 12 where VL is the voltage drop across the inductor, VF is the forward voltage of the output catch diode, and VSW is the voltage drop across the power switch. VL+VSW can be approximated at 0.4V and VF can be approximated at 0.4V. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9 APPLICATIONS INDUCTOR CURRENT LIMIT PROGRAMMING Setting of the peak inductor current limit is an important aspect of the PFM constant off-time architecture; it determines the maximum output power capability and has a marked effect on efficiency. It is recommended that the peak inductor current be set to approximately two times the expected maximum DC input current. This setting will minimize the inductor size, the input ripple current, and the output ripple voltage. Care should be taken to use inductors that will not saturate at the peak inductor current level. The desired peak inductor current can be estimated by the following equation: IPK − 0.185 30 ⋅ 10 −6 which is taken from the following graph (Figure 7). eq. 9 where VOVP is the desired maximum voltage on the output. This voltage should be selected to accommodate the maximum forward voltage of all the LEDs, over temperature, plus the maximum feedback voltage. Conversely, it may also be selected according to the maximum VDS voltage of the output MOSFET. IPK = 2 ⋅ R CS ≅ Peak Inductor Current (mA) POWER MOSFET SELECTION The LX1744 can source up to 100mA of gate current. A logi-level N-channel MOSFET with a low turn on threshold voltage, low gate charge and low RDS(ON) is required to optimize overall circuit performance. can be chosen from the following equation: WWW . Microsemi .C OM negative voltage transition that is greater than the output voltage. LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET APPLICATION NOTE VBAT = 1.6V to 6.0V D3 - VOUT D4 LX1744 VOUT achieved by placing a feed-forward capacitor across the feedback resistor connected to the LCD Bias output (Figure 2). A recommended value of 1nF should be used. PCB LAYOUT Minimizing trace lengths from the IC to the inductor, diode, input and output capacitors, and feedback connection (i.e. pin 3) are typical considerations. Moreover, the designer should maximize the DC input and output trace widths to accommodate peak current levels associated with this circuit. SW FB WWW . Microsemi .C OM NEGATIVE LCD BIAS GENERATION For applications that require it, a negative bias can be easily generated using an inductorless charge pump consisting of only four additional discrete components (Figure 8). R1 R2 Figure 8 – Negative Bias Generation This negative output is a mirror of the positive output voltage. However, it is unregulated. If a regulated negative bias is desired then this is also possible with some additional components. A low current shunt regulator (LX6431 or LX432) and a bipolor pass element can form a simple negative voltage LDO (Figure 9). D3 VBAT = 1.6V to 6.0V VNEG_LCD D4 R3 R4 LX1744 LX6431, LX432 VOUT R5 SWx FBx R1 R2 Figure 9 – Regulated Negative Bias ⎛ R ⎞ VNEG _ LCD = VREF ⋅ ⎜⎜1 + 4 ⎟⎟ ⎝ R5 ⎠ APPLICATIONS R3 is sized to meet the minimum shunt current required for regulation while R4 and R5 are calculated. If R5 is selected to be 100kΩ then R4 is calculated using the following equation: eq. 13 where VREF is a -2.5V in the case of the LX6431. FEED-FORWARD CAPACITANCE Improved efficiency and ripple performance can be Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 LX1744 I N T E G R A T E D P R O D U C T S Dual Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET EVALUATION BOARD Name Input/Output Range VIN 0 to 6V GNDx 0V ADJ 0 to VIN-100mV SHDN 0 to VIN WWW . Microsemi .C OM Table 1: Input and Output Pin Assignments Description Main power supply for outputs. Common ground reference. Apply a DC voltage or a PWM voltage to this pin to adjust the LCD1 output voltage. PWM inputs should be greater than 120Hz. Pulled up to VIN on board (10KΩ), Ground to inhibit the LED driver output (VOUT). SHDN Pulled up to VIN on board (10KΩ), Ground to inhibit the VLCD1. VLCD ≤25V Output voltage test point. Programmed for 18V output, adjustable up to 25V. -VLCD ≥-25V Output voltage mirror of VLCD1 VOUT ≤25V LED drive voltage probe point. LFB 0 to VIN LED current sense feedback. BRT 0 to 350mV DRV 0 to VIN REF 1.19V Typ. Apply a DC voltage or a PWM voltage to this pin to adjust the LED current. PWM inputs should be greater than 120Hz with a DC portion less than 350mV. LED Driver MOSFET Gate Driver Output Buffered IC reference output. Note: All pins are referenced to ground. APPLICATIONS Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 11 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET EVALUATION BOARD Jumper Position J1 N/A Close to adjust LED current with on-board potentiometer. J2 N/A Close to adjust VLCD with on-board potentiometer. J3 N/A Remove the factory installed jumper and insert a 4~6cm wire loop (optional) to observe the inductor current waveform using a current probe. J4 N/A Remove jumper to test open-circuit over-voltage protection implemented with R1 and R2 WWW . Microsemi .C OM Table 3: Jumper Position Assignments Function Note: All pins are referenced to ground. Table 4: Factory Installed Component List Ref Part Description C1 CAPACITOR, 4.7µF, 1210, 6.3V C2, C7 CAPACITOR, 4.7µF, 1210, 35V C3, C4 CAPACITOR, 1000pF, 0805, 35V C5, C6 CAPACITOR, (SPARE), See Note 1 C8, C9 CAPACITOR, 1µF, 0805, 35V C10, C12 CAPACITOR, 0.1µF, 0805, 6.3V C11 CAPACITOR, 2.2µF, 0805, 16V CR1, CR2, CR3, CR4 LED1, LED2, LED3, LED4 L1, L2 Q1 Microsemi UPS5819, SCHOTTKY, 1A, 40V, POWERMITE Microsemi UPWLEDxx, LED, Optomite INDUCTOR, 47µH, 480mA, SMT FDV303N MOSFET, 30V, SOT-23 R1, R3 RESISTOR, 1M, 1/16W, 0805 R2, R6 RESISTOR, 75K, 1/16W, 0805 R4 RESISTOR, 1K, 1/16W, 0805 R5 RESISTOR, 15, 1/16W, 0805 R7, R8 RESISTOR, 100K, POT, 1/16W, 0805 RESISTOR, 100K, 1/16W, 0805 R9, R10 R11, R12, R13 RESISTOR, 10K, 1/16W, 0805 U1 Microsemi LX1744CPW BOOST CONTROLLER 1. APPLICATIONS Notes Use these locations to insert additional input and/or output capacitance. Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 12 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET EVALUATION BOARD 47.0uH 10K C8 CR2 /SHDN SW FB /SHDN ADJ DRV SRC OVP LFB CS /LSHDN BRT REF 2 FDV303N 12 13 10 9 11 7 8 5 + R1 C3 1000pF 1M 1K R2 R8 1 GND 1 + C5 spare LED3 72K R7 LED4 VIN 1 ADJ C2 4.7uF 35V LED2 1 R6 72K LED1 R4 C10 .1uF 1 C4 1M 1000pF C7 4.7uF 35V IN J3 UPS5819 2 R3 UPS5819 + 6 4 1uF Q1 47.0uH R11 U1 LX1744TSSOP 1 3 2 1 1 J1 L2 GND GND NC C1 4.7uF 6.3V CR3 1 C9 UPS5819 1uF CR4 VLCD + 2 -VLCD C6 spare 2 14 15 16 + CR1 J3 L1 1 J2 Vin test points VOUT 1 test points 1 DRV WWW . Microsemi .C OM 1 1 LFB R5 R9 R12 10K 100K + C11 2.2uF 16V 15 R10 1 GND2 1 /LSHDN 1 BRT 100K C12 .1uF Figure 10 – LX1744EVAL Evaluation Board Schematic APPLICATIONS Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 13 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET VOUT VERSUS VADJ GATE DRIVE 6 DRV Voltage (V) Output Voltage (V) WWW . Microsemi .C OM 30 25 20 15 10 5 0 5 4 3 2 1 0 0 0.5 1 1.5 2 0 20 40 Adjustment Signal Voltage (VADJx) 60 80 100 120 140 160 DRV Current (mA) Figure 10 – Output Voltage Vs. Adjustment Signal Threshold Figure 11 – Gate Drive Voltage Vs. Drive Current Note: The LX1744 uses the internal voltage reference until the VADJ signal exceeds 0.5V (typ). VIN = 5V, TA = 25°C EFFICIENCY Efficiency WAVEFORM 90% 85% 80% 75% 70% 65% 60% 55% 50% 0 5 10 15 20 25 Output Current (mA) Figure 13 – LED Driver (Upper) and LCD Bias Efficiency Figure 12 – Typical Switching Waveform CH1 – SWx Voltage, CH2 – Output Voltage, CH3 – Inductor Current VIN = 5V, Four LEDs, L = 47µH, RCS = 4kΩ VIN = 3.6V, VOUT = 5.5V, L = 47µH VIN = 3.6V, VOUT = 18V, IOUT = 9mA CHARTS Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 14 LX1744 I N T E G R A T E D Dual Output Boost – LED Driver / LCD Bias P R O D U C T S P RODUCTION D ATASHEET PACKAGE DIMENSIONS 14-Pin Thin Small Shrink Outline Package (TSSOP) P E 1 23 F D A H SEATING PLANE LQ WWW . Microsemi .C OM PW B G L C M DIM A B C D E F G H L M P *LC MILLIMETERS MIN MAX 0.85 0.95 0.17 0.27 0.09 0.20 4.90 5.10 4.30 4.50 0.65 BSC 0.05 0.15 1.10 0.45 0.75 0° 8° 6.4 BSC 0.10 INCHES MIN MAX 0.033 0.037 0.007 0.011 0.004 0.008 0.193 0.201 0.169 0.177 0.026 BSC 0.002 0.006 0.043 0.0177 0.030 0° 8° 0.252 BSC 0.004 16-Pin Micro Leadframe Package - Quad Package (MLPQ) D b D2 E E2 e K L MILLIMETERS MIN MAX 0.80 1.00 0 0.05 0.18 0.30 0.23 0.38 4.00 BSC 4.00 BSC 0.65 BSC 2.55 2.80 2.55 2.80 0.20 0.30 0.50 INCHES MIN MAX 0.031 0.039 0 0.002 0.007 0.012 0.009 0.015 0.157 BSC 0.157 BSC 0.026 BSC 0.100 0.110 0.100 0.110 0.008 0.012 0.020 A3 Note: Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side. Lead dimension shall not include solder coverage. Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 15 MECHANICALS A A1 DIM A A1 A3 b D E e D2 E2 K L LX1744 I N T E G R A T E D P R O D U C T S Dual Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET NOTES WWW . Microsemi .C OM NOTES PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time. Copyright © 2000 Rev. 1.1b, 2005-03-01 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 16