LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET KEY FEATURES DESCRIPTION guaranteed at a VIN 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 LX1745 is capable of achieving an LED drive in excess of 1.0W. The LX1745 provides simple dynamic adjustment of the LED drive current (0% to 100% full range dimming) and the LCD Bias output voltages (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 LX1745 is available in the lowprofile 20-Pin TSSOP. > 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 Two LCD Bias Voltage Adjustments Via Analog Reference Or Direct PWM Input 20-Pin TSSOP Package WWW . Microsemi .C OM The LX1745 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 voltages with an additional two integrated boost converters. Designed for maximum efficiency and featuring a psuedo-hysteretic PFM topology (that decreases output voltage ripple), the LX1745 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 for LCD Bias generation, the LED driver utilizes an external N-Channel MOSFET in order to maintain maximum efficiency along with flexible power requirements.. The LX1745’s control circuitry is optimized for portable systems with a shutdown current of less than 1µA. The input voltage range of 1.6V to 6.0 allows for a wide selection of system battery voltages and start-up is 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 LX1745 ON OFF LSHDN SW2 RSET 15Ω BRT REF FB2 GND VLCD2 = VIN to 25V SHDN2 ON OFF SHDN1 ADJ1 ADJ2 LX1745 Evaluation Board ON OFF LX1745 PACKAGE ORDER INFO PW TA (°C) Plastic TSSOP 20-Pin RoHS Compliant / Pb-free Transition DC: 0442 -40 to 85 LX1745CPW Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1745CPW-TR) Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET PACKAGE PIN OUT Supply Input Voltage ...........................................................................-0.3V to 7V Feedback Input Voltage (VFBx) ...............................................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN x) ..........................................-0.3V to VIN + 0.3V PWM Input Amplitude (ADJx, BRT).....................................-0.3V to VIN + 0.3V Analog Adjust Input Voltage (VADJx, VBRT)............................-0.3V to VIN + 0.3V SRC Input Current ................................................................................ 500mARMS Operating Temperature Range .........................................................-40°C to 85°C Maximum Operating Junction Temperature ................................................ 150°C Storage Temperature Range...........................................................-65°C to 150°C RoHS / Pb-free Peak Package Solder Reflow Temperature (40 second maximum exposure) ..................................................... 260°C (+0, -5) SW1 ADJ1 SHDN1 IN LSHDN DRV SRC GND SHDN2 SW2 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11 WWW . Microsemi .C OM ABSOLUTE MAXIMUM RATINGS GND FB1 REF OVP BRT CS LFB ADJ2 FB2 GND PW PACKAGE (Top View) RoHS / Pb-free 100% Matte Tin Lead Finish 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. x denotes respective pin designator 1, 2, or 3 THERMAL DATA PW Plastic TSSOP 20-Pin 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1745 TM ® Triple Output Boost – LED Driver / LCD Bias 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. SWx LCD Bias Inductor Switch Connection – Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. FBx 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. ADJx 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET ELECTRICAL CHARACTERISTICS Parameter ` LFB Threshold Voltage VLFB LFB Input Bias Current BRT Input Voltage Range BRT Input Bias Current LED Driver Shutdown Input Bias Current Current Sense Bias Current ILFB VBRT IBRT DRV Sink/Source Current DRV On-Resistance Maximum Switch On-Time Minimum Switch Off-Time OVP Threshold Voltage Reference Voltage Min LX1745 Typ Max Units I SHDN1 VBRT = 100mV VBRT = 20mV VLFB = 100mV 85 5 -100 0 BRT = 100mv 0.0V ≤ SHDN1 ≤ VIN -100 ICS IPK RDRV(ON) tON tOFF VOVP VREF 100 20 RCS = 0kΩ RCS = 2kΩ VIN = 5V, VDRV = 3V VCC = 5V VFB = 1V VFB = 1V 85 115 35 100 VIN 60 100 4 170 210 100 12 200 1.15 1.186 300 1.21 1.21 1.166 1.190 mV nA V nA nA μA mA 15 ∞ 410 1.26 1.234 mA Ω μS nS V LCD BIAS Output Voltage Range FBx Threshold Voltage FBx Input Current LCD Bias Shutdown Input Bias Current Peak Inductor Current Internal NFET On-resistance Switch Pin Leakage Current Switch On-Time Switch Off-Time ADJx Input Voltage Range ADJx Input Bias Current ` Test Conditions 70°C except where LED DRIVER Switch Peak Current ` 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, LSHDN = VIN, SHDN1 = VIN, SHDN2 = VIN ENTIRE REGULATOR Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Shutdown High Input Voltage Shutdown Low Input Voltage Copyright © 2000 Rev. 1.2, 2006-02-27 VFB = 1.4V I SHDNx SHDNx = GND ILIM RDS(ON) ILEAK tON tOFF VADJx IADJx TA = +25°C ISW = 10mA, TA = +25°C, VIN = 5V VSW = 25V VFB = 1V VFB = 1V VIN 150 0.9 1.6 TA = +25°C κ V SHDNx V SHDNx IQ V V nA 100 nA 1.0 ∞ 400 1.5 1.0 mA Ω μA μs ns V μA 6.0 1.6 V V 330 1.1 0.3 Recommended Operating Range 25 1.214 200 -2 VIN = 2V VIN = 2V VFBx = 1.4V, VLFB > VBRT – 0.1V VFBx = 1.4V, VLFB > VBRT – 0.1V, V LSHDN < 0.4V VFBx = 1.4V, VLFB > VBRT – 0.1V, V SHDN1 < 0.4V VFBx = 1.4V, VLFB > VBRT – 0.1V, V SHDN2 < 0.4V V SHDN1 < 0.4V, V SHDN2 < 0.4V, V LSHDN < 0.4V mV/°C 1.6 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 200 0.4 320 0.35 1 140 220 80 120 0.35 1 V V ELECTRICALS Quiescent Current VOUT VFB IFB μA Page 4 LX1745 ® TM Triple 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 2.5MΩ GND Current Limit 4μA CS Shutdown Logic IN LSHDN SHDNx OVP FBx Control Logic REF Reference Logic ADJx 50pF 2.5MΩ Driver SWx Current Limit Voltage Reference FBx Control Logic Driver SWx Reference Logic Current Limit BLOCK DIAGRAM ADJx 50pF 2.5MΩ Figure 1 – Simplified Block Diagram Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET APPLICATION CIRCUITS WWW . Microsemi .C OM ILED = 20mA to 0mA D1 L1 VBAT = 1.6V to 6.0V 47μH 1206 Case Size L2 L3 D3 - VLCD D4 C1 4.7μF R5 DRV IN SRC SW1 D2 VLCD1 = VIN to 25V R6 OVP LFB FB1 (Feedforward Capacitor) R1 CS LX1745 LSHDN D3 R2 SW2 RCS ON OFF RLED 15Ω (typ) BRT REF FB2 R3 VLCD2 = VIN to 25V GND SHDN2 SHDN1 ON OFF ADJ1 ADJ2 R4 ON OFF Figure 2 – LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via PWM Input APPLICATIONS Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias 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 = R2 VOUT - VREF VREF eq. 1 LCD BIAS – OUTPUT VOLTAGE ADJUSTMENT The LX1745 allows for the dynamic adjustment of each of the voltage outputs via an adjustment pin (ADJx). Any voltage applied to the adjustment pin(s) works in conjunction with the internal reference logic. The LX1745 will automatically utilize the internal reference when no signal is detected or when the adjustment signal voltage is below approximately 0.6V. Each of these pins 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). LX1745 Reference Logic 50pF ADJx WWW . Microsemi .C OM FUNCTIONAL DESCRIPTION The LX1745 is a triple 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 outputs. 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 14. RADJx_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 VADJX value is equal to the reference voltage (eq. 2) ⎛ ⎞ 2.5MΩ ⎟ VADJx = VPWM ⋅ Duty Cycle ⋅ ⎜ ⎜ 2.5MΩ + R ⎟ PWM _ 1 ⎠ ⎝ eq. 2 VBAT = 1.6V to 6.0V LX1745 SWx RADJx_1 ADJx R1 CADJx R2 Figure 5 – LCD Bias Adjustment Input Filter Figure 3 – LCD Bias Output Voltage Copyright © 2000 Rev. 1.2, 2006-02-27 LX1745 FBx RADJx_2 Ideally the resultant ripple on the ADJx 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 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias 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 = VBRTx(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 (ADJx) pins, 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 LX1745 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 LX1745 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. 1.2, 2006-02-27 5 π ⋅ fPWM LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias 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 LX1745 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. ROVP _ 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. 1.2, 2006-02-27 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: ⎞ eq. ⎛ L ⋅ I ⋅ I ⎞⎛ 1 IPK ⋅ IOUT VRIPPLE ≅ ⎜⎜ PK OUT ⎟⎟⎜⎜ + ⎟⎟ C V ( V V ) V V V − + + − OUT SW L OUT F IN ⎠ ⎠⎝ IN ⎝ 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 ⋅ RCS ≅ Peak Inductor Current (mA) POWER MOSFET SELECTION The LX1745 can source up to 100mA of gate current. An logic 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. LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET APPLICATION NOTE VBAT = 1.6V to 6.0V D3 - VOUT D4 LX1745 VOUT achieved by placing a feed-forward capacitor across the feedback resistor connected to the 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. SWx FBx 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 SHDN 0 0 1 1 1 0 1 0 SHDN2 0 1 0 1 1 1 0 0 SHDN1 1 1 1 1 0 0 0 0 LCD1 1 1 1 1 0 0 0 0 LCD2 0 1 0 1 0 0 0 0 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). LED 0 0 1 1 0 0 0 0 Table 1 – Enable Logic VBAT = 1.6V to 6.0V VNEG_LCD D4 R3 R4 LX1745 LX6431, LX432 R5 VOUT 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET EVALUATION BOARD Name VIN 0 to 6V GND 0V ADJ1 0 to VIN-100mV 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. ADJ2 Apply a DC voltage or a PWM voltage to this pin to adjust the LCD2 output voltage. PWM inputs should be greater than 120Hz. SHDN Pulled up to VIN on board (10KΩ), Ground to inhibit the LED driver output (VOUT). SHDN1 0 to VIN SHDN2 WWW . Microsemi .C OM Table 2: Input and Output Pin Assignments Input/Output Range Pulled up to VIN on board (10KΩ), Ground to inhibit the VLCD1. Pulled up to VIN on board (10KΩ), Ground to inhibit the VLCD2. VLCD1 ≤25V Output voltage test point. Programmed for 18V output, adjustable up to 25V. -VLCD ≥-25V Output voltage mirror of VLCD1 VLCD2 ≤25V Output voltage test point. Programmed for 22V output, adjustable up to 25V. VOUT ≤25V LED drive voltage probe point. FDBK 0 to VIN LED current sense feedback. BRT 0 to 350mV 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. REF 1.19V Typ. Buffered IC reference output. Note: All pins are referenced to ground. APPLICATIONS Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 11 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET EVALUATION BOARD Position JU1 N/A JU2 N/A JU3 N/A JU4 N/A WWW . Microsemi .C OM Table 3: Jumper Position Assignments Jumper Function Remove the factory installed jumper and insert a 4~6cm wire loop (optional) to observe the inductor current waveform using a current probe. Remove jumper to test open-circuit over-voltage protection implemented with R1 and R2 Note: All pins are referenced to ground. Table 4: Factory Installed Component List Ref Part Description C1 CAPACITOR, 4.7μF, 1210, 6.3V C2, C5, C6 CAPACITOR, 4.7μF, 1210, 35V C3, C7, C8 CAPACITOR, 1000pF, 0805, 35V C4, C11 CAPACITOR, (SPARE), See Note 1 C9, C10, C12, CAPACITOR, 1μF, 0805, 35V C13 CR1, CR2, Microsemi UPS5819, SCHOTTKY, 1A, 40V, POWERMITE CR3, CR4, CR5 LED1, LED2, LED3, LED4 Microsemi UPWLEDxx, LED, Optomite L1, L2, L3 INDUCTOR, 47μH, 480mA, SMT Q1 FDV303N MOSFET, 30V, SOT-23 R1, R5 RESISTOR, 1M, 1/16W, 0805 R2, R6, R8 RESISTOR, 75K, 1/16W, 0805 R3 RESISTOR, 15, 1/16W, 0805 R4 RESISTOR, 4.02K, 1/16W, 0805 R7 RESISTOR, 1.25M, 1/16W, 0805 R9, R10, R11 RESISTOR, 10K, 1/16W, 0805 R12, R13 RESISTOR, 100K, 1/16W, 0805 U1 Microsemi LX1745CPW BOOST CONTROLLER Notes 1. Use these locations to insert additional input and/or output capacitance. APPLICATIONS Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 12 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET EVALUATION BOARD Vin 1 GND 1 JU1 L1 +C4 spare R9 R10 10K 10K ADJ1 1 SHDN1 1 SHDN 1 SHDN2 1 CR1 L2 C9 1uF L3 1 2 3 4 5 6 7 8 9 10 1 JU3 2 1 UPS5819 SW1 LCDGND1 ADJ1 FB1 REF SHDN1 VIN OVP BRT SHDN DRV CS SRC LFB LEDGND ADJ2 SHDN2 FB2 SW2 LCDGND2 1 C6 4.7uF 35V + C7 1000pF + C2 4.7uF 35V + C11 Spare R2 72K 20 19 18 17 16 15 14 13 12 11 1 GND 1 FDBK 1 ADJ2 1 BRT LED 4 LED 3 LED 2 LED 1 R4 LX1745 VLCD2 VOUT 1 R1 C3 1M 1000pF UPS5819 C10 1uF CR4 4.02K CR3 22V 1 JU4 CR5 U1 JU2 2 REF 2 UPS5819 Q1 FDV303N R11 10K 1 R13 100K 2 47.0uH C1 4.7uF 6.3V + 1 -VLCD WWW . Microsemi .C OM C12 1uF 1 R3 15 UPS5819 R7 1.25M R12 100K R8 72K C13 1uF CR2 UPS5819 18V C5 4.7uF 35V + C8 1000pF 1 VLCD1 R5 1M R6 72K Figure 10 – LX1745EVAL Evaluation Board Schematic APPLICATIONS Figure 11 – LX1745EVAL Evaluation Board Copyright © 2000 Rev. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 13 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias 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 12 – Output Voltage Vs. Adjustment Signal Threshold Figure 13 – Gate Drive Voltage Vs. Drive Current Note: The LX1745 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 15 – LED Driver (Upper) and LCD Bias Efficiency Figure 14 – 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 14 LX1745 ® TM Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET PACKAGE DIMENSIONS WWW . Microsemi .C OM PW 20-Pin Thin Small Shrink Outline Package (TSSOP) 3 2 1 E E1 e D 1 A2 A SEATING PLANE A1 MILLIMETERS MIN MAX 1.10 0.05 0.15 0.80 1.05 0.19 0.30 0.09 0.20 6.40 6.60 6.25 6.55 4.30 4.50 0.65 BSC 0.45 0.75 0° 8° 0.10 L c INCHES MIN MAX 0.043 0.002 0.006 0.031 0.041 0.007 0.012 0.004 0.008 0.252 0.260 0.246 0.258 0.169 0.177 0.026 BSC 0.018 0.030 0° 8° 0.004 * Lead Coplanarity 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 15 MECHANICALS Dim A A1 A2 b c D E E1 e L Θ1 *LC b LX1745 TM ® Triple 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. 1.2, 2006-02-27 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 16