LX1745

LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET DESCRIPTION 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 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. KEY FEATURES > 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 APPLICATIONS WWW . Microsemi . C OM 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 L1 ILED = 20mA to 0mA C1 4.7µF VBAT = 1.6V to 6.0V - VLCD 47µH 1206 Case Size DRV IN SRC VLCD1 = VIN to 25V SW1 OVP LFB FB1 CS LX1745 LSHDN SW2 REF FB2 GND SHDN1 ADJ1 ADJ2 BRT ON OFF RSET 15Ω ON OFF VLCD2 = VIN to 25V SHDN2 ON OFF LX1745 Evaluation Board LX1745 LX1745 PACKAGE ORDER INFO TA (°C) -40 to 85 PW 20-Pin Plastic TSSOP LX1745-CPW Note: Available in Tape & Reel. Append the letter “T” to the part number. (i.e. LX1745-CPWT) Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET ABSOLUTE MAXIMUM RATINGS 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 Lead Temperature (Soldering 10 seconds) .................................................. 300°C 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 WWW . Microsemi . C OM 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 GND FB1 REF OVP BRT CS LFB ADJ2 FB2 GND PW PACKAGE (Top View) THERMAL DATA PW Plastic TSSOP 20-Pin 90°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 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 PACKAGE DATA Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET FUNCTIONAL PIN DESCRIPTION Name IN DRV SRC OVP LFB GND BRT REF SWx FBx Description 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. LED MOSFET Gate Driver – Connects to an external N-Channel MOSFET. LED MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source. 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 LED Current Feedback Input – Connects to a current sense resistor between the LED output load and GND to set the LED drive current. Common terminal for ground reference. 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. Buffered Reference Output – Connected to the internal bandgap reference voltage of 1.2V. LCD Bias Inductor Switch Connection – Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. 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. 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. 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. 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. Current-Sense Amplifier Input – Connecting a resistor between CS and GND sets the peak inductor current limit. WWW . Microsemi . C OM ADJx LSHDN SHDNx CS PACKAGE DATA PACKAGE DATA Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET 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 Parameter LED DRIVER ELECTRICAL CHARACTERISTICS ≤ 70°C except where WWW . Microsemi . C OM Symbol Test Conditions VBRT = 100mV VBRT = 20mV VLFB = 100mV BRT = 100mv 0.0V ≤ SHDN1 ≤ VIN RCS = 0kΩ RCS = 2kΩ VIN = 5V, VDRV = 3V VCC = 5V VFB = 1V VFB = 1V Min 85 5 -100 0 -100 LX1745 Typ 100 20 Max 115 35 100 VIN 60 100 Units LFB Threshold Voltage LFB Input Bias Current BRT Input Voltage Range BRT Input Bias Current LED Driver Shutdown Input Bias Current Current Sense Bias Current Switch Peak Current DRV Sink/Source Current DRV On-Resistance Maximum Switch On-Time Minimum Switch Off-Time OVP Threshold Voltage Reference Voltage LCD BIAS VLFB ILFB VBRT IBRT I SHDN1 ICS IPK RDRV(ON) tON tOFF VOVP VREF VOUT VFB IFB I SHDNx ILIM RDS(ON) ILEAK tON tOFF VADJx IADJx VIN κ V SHDNx V SHDNx mV nA V nA nA µA mA 85 4 170 210 100 12 300 1.21 1.21 1.190 200 1.15 1.186 1.166 15 ∞ 410 1.26 1.234 25 1.214 200 100 mA Ω µS nS V V V nA nA mA Ω µA µs ns V µA V V mV/°C V V 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 ENTIRE REGULATOR Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Shutdown High Input Voltage Shutdown Low Input Voltage VFB = 1.4V SHDNx = GND TA = +25°C ISW = 10mA, TA = +25°C, VIN = 5V VSW = 25V VFB = 1V VFB = 1V 330 1.1 150 0.9 0.3 1.0 ∞ 400 1.5 1.0 6.0 1.6 Recommended Operating Range 1.6 -2 TA = +25°C 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 1.6 200 0.35 140 80 0.35 0.4 320 1 220 120 1 E ELECTRICALS Quiescent Current IQ µA Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET SIMPLIFIED BLOCK DIAGRAM WWW . Microsemi . C OM LFB Control Logic Driver DRV SRC BRT 50pF 2.5MΩ Reference Logic Current Limit GND 4µA CS Shutdown Logic LSHDN SHDNx FBx Control Logic SWx IN OVP REF Driver ADJx 50pF 2.5MΩ Reference Logic Current Limit Voltage Reference Control Logic Reference Logic 50pF 2.5MΩ Driver FBx SWx ADJx Current Limit B D BLOCK DIAGRAM Figure 1 – Simplified Block Diagram Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET APPLICATION CIRCUITS WWW . Microsemi . C OM ILED = 20mA to 0mA L1 D1 VBAT = 1.6V to 6.0V D3 47µH 1206 Case Size L2 L3 R5 - VLCD D4 C1 4.7µF DRV IN SRC R6 SW1 D2 OVP LFB VLCD1 = VIN to 25V (Feedforward Capacitor) FB1 R1 CS RCS LX1745 LSHDN D3 SW2 REF FB2 R3 GND SHDN2 SHDN1 ADJ1 ADJ2 ON OFF RLED 15Ω (typ) R2 BRT ON OFF VLCD2 = VIN to 25V R4 ON OFF Figure 2 – LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via PWM Input A APPLICATIONS Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET APPLICATION NOTE 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. 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. VBAT = 1.6V to 6.0V 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 WWW . Microsemi . C OM 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 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 LX1745 VOUT R1 SWx FBx LX1745 ADJx CADJx RADJx_1 APPLICATIONS APPLICATIONS RADJx_2 R2 Figure 5 – LCD Bias Adjustment Input Filter Figure 3 – LCD Bias Output Voltage 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 Copyright  2000 Rev. 1.1a, 2004-02-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1745 INTEGRATED PRODUCTS Triple Output Boost – LED Driver / LCD Bias P RODUCTION D ATASHEET APPLICATION NOTE 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. CPWM = 50 π ⋅ fPWM ⋅ RPWM _ 1 eq. 3 where RPWM _ 1