LX1992CDU

LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET DESCRIPTION KEY FEATURES W WW . Microsemi . C OM The LX1992 is a compact high efficiency step-up boost controller for driving white or color LEDs in backlight or frontlight systems and offers designers maximum flexibility with respect to efficiency and cost. The LX1992 features a pseudohysteretic pulse frequency modulation topology and uses an external NChannel MOSFET. Further, the LX1992 features control circuitry that is optimized for portable systems (e.g., quiescent supply current of 80µA (typ) and a shutdown current of less than 1µA). These design enhancements provide for improved performance in battery operated systems applications. The device input voltage range is from 1.6V to 6.0, allowing for a wide selection of system battery voltages and start-up operation is guaranteed at 1.6V input. Programming the output current is readily achieved by 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). Moreover, the LX1992 is capable of achieving output currents in excess of 150mA, depending on the MOSFET selected. The LX1992 has an additional feature for simple dynamic adjustment of the output current (i.e., up to 100% of the maximum programmed current). Designers can make this adjustment via an analog reference signal or a direct PWM generated signal applied to the ADJ pin and any PWM amplitude is easily accommodated with a single external resistor. The LX1992 is available in both the 8Pin MSOP, and the miniature 8-Pin MLP requiring minimal PCB area. > 90% Efficiency 80µA Typical Quiescent Supply Current Externally Programmable Peak Inductor Current Limit For Maximum Efficiency Logic Controlled Shutdown < 1µA Shutdown Current Dynamic Output Current Adjustment Via Analog Reference Or Direct PWM Input 8-Pin MSOP Package or 8-Pin MLP APPLICATIONS/BENEFITS Pagers Wireless Phones PDAs Handheld Computers General LCD Bias Applications LED Driver Digital Camera Displays IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT L1 V BAT = 1 .6V to 6.0V 47 µ H 1206 C ase Size C1 4.7 µ F DR V IN SR C ON O FF SHD N LX1992 FB ADJ GND CS R CS 4 kΩ V F = 3 .6V typ. I LED = 2 0mA to 0mA R SET 15Ω LX1992 LX1992 TA (°C) 0 to 70 Copyright © 2000 Rev. 1.1b, 2005-03-03 PACKAGE ORDER INFO Plastic MLP Plastic MSOP LM 8-Pin DU 8-Pin RoHS Compliant / Pb-free Transition DC: 0452 RoHS Compliant / Pb-free Transition DC: 0432 LX1992CLM LX1992CDU Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1992CDU-TR) Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT SRC GND CS ADJ 1 2 3 4 8 7 6 5 DRV IN FB SHDN W WW . Microsemi . C OM Supply Voltage (VIN) ........................................................................-0.3V to 7.0V Feedback Input Voltage (VFB) ................................................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN ) ...........................................-0.3V to VIN + 0.3V Analog Adjust Input Voltage (VADJ).......................................-0.3V to VIN + 0.3V Source Input Current (ISRC).................................................................... 0.80 ARMS Operating Junction Temperature.................................................................. 150°C Storage Temperature Range...........................................................-65°C to 150°C Lead Temperature (Soldering 180 seconds) ................................................ 235°C Peak Package Solder Reflow Temp. (40 second max. exposure) ... 260°C (+0, -5) 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. DU P ACK AGE (Top View) SRC GND CS 1 2 3 4 LM P ACK AGE (Top View) 8 7 6 5 DRV IN FB SHDN THERMAL DATA ADJ DU Plastic MSOP 8-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA THERMAL RESISTANCE-JUNCTION TO CASE, θJC 206°C/W 39°C/W RoHS / Pb-free 100% Matte Tin Lead Finish LM Plastic MLP 8-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA THERMAL RESISTANCE-JUNCTION TO CASE, θJC 41°C/W 5.2°C/W Junction Temperature Calculation: TJ = TA + (PD x θJC). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. FUNCTIONAL PIN DESCRIPTION NAME IN FB 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. Feedback Input – Connects to a current sense resistor between the output load and GND to set the output current. Active-Low Shutdown Input – A logic low shuts down the device and reduces the supply current to 0.2µA (Typ). Connect SHDN to VCC for normal operation. MOSFET Gate Driver – Connects to an external N-Channel MOSFET. Current-Sense Amplifier Input – Connecting a resistor between CS and GND sets the peak inductor current limit. Common terminal for ground reference. Adjustment Signal Input – Provides the internal reference, via an internal filter and gain resistor, allowing a dynamic output current adjustment corresponding to a varying duty cycle. The actual ADJ pin voltage range is from VIN to GND. In order to minimize the current sense resistor power dissipation a practical range of VADJ = 0.0V to 0.5V should be used. MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source. SHDN DRV CS GND ADJ SRC PACKAGE DATA PACKAGE DATA Note: ADJ pin should not be left floating. Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET ELECTRICAL CHARACTERISTICS Unless otherwise specified, the following specifications apply over the operating ambient temperature 0°C ≤ TA otherwise noted and the following test conditions: VIN = 3V, ILOAD = 20mA, SHDN = VIN, and VADJ = 300mV. Parameter Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Quiescent Current FB Threshold Voltage FB Input Bias Current ADJ Input Voltage Range ADJ Input Bias Current Shutdown Input Bias Current Shutdown High Input Voltage Shutdown Low Input Voltage Current Sense Bias Current Minimum Peak Current Efficiency NDRV Sink Current NDRV Source Current Off-Time W WW . Microsemi . C OM ≤ 70°C except where Symbol VIN VSU kVST Test Conditions Min 1.6 LX1992 Typ Max 6.0 1.6 Units V V mV/°C µA µA mV nA V nA nA V V µA mA % mA mA ns TA = +25°C -2 VFB > 0.3V V SHDN < 0.4V VFB = 0.3V IOUT = (VADJ)/(RSET) VADJ < 0.3V SHDN = GND 50 0.2 300 IQ VFB IFB VADJ IADJ I SHDN V SHDN V SHDN ICS IMIN η ISNK ISRC tOFF 275 -100 0.0 -150 -50 1.6 3.0 53 100 0.5 325 100 VIN 0 50 0.4 7.0 83 VFB < 0.3V RCS = 560Ω VIN = 3.0V, ILOAD = 20mA VIN = 5V VIN = 5V VFB = 0.3V; VADJ=0.5V 5.0 85 50 100 100 500 SIMPLIFIED BLOCK DIAGRAM FB A DRV Reference Logic 50pF 2.5M Ω B 5µA SRC C ontrol Logic Driver GND ADJ CS ELECTRICALS ELECTRICALS IN Shutdown Logic SHDN Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET APPLICATION CIRCUITS W WW . Microsemi . C OM Typical LED Driver Applications L1 V BAT = 1 .6V to 6.0V 47 µ H 1206 Case Size C1 4.7 µ F DRV IN SR C ON OFF SHDN LX1992 FB ADJ G ND CS R CS 4 kΩ V F = 3 .6V typ. I LED = 0 mA to 20mA Figure 1 – LED Driver with Full-Range Dimming Via PWM Input L1 R SET 15Ω V BAT = 1 .6V to 6.0V 47 µ H 1206 Case Size C1 4.7 µ F DRV IN SR C ON OFF SHDN LX1992 FB ADJ CS G ND R CS 4 kΩ V AD J = 0 .0V to 0.3V + - APPLICATION APPLICATION R SET V F = 3 .6V typ. I LED = 0 mA to 20mA Figure 2 – LED Driver with Full-Range Dimming Via Analog Voltage Input 15Ω 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, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET APPLICATION INFORMATION W WW . Microsemi . C OM OPERATING THEORY The LX1992 is a PFM boost converter that is optimized for driving a string of series connected LEDs. It operates in a pseudo-hysteretic mode with a fixed switch “off time” of 300ns. Converter switching is enabled as LED current decreases causing the voltage across RSET to decrease to a value less than the voltage at the VADJ pin. When the voltage across RSET (i.e., VFB) is less than VADJ, comparator A activates the control logic. The control logic activates the DRV output circuit that connects to the gate of the external FET. The DRV output is switched “on” (and remains “on”) until the inductor current ramps up to the peak current level. This current level is set via the external RCS resistor and monitored through the CS and SRC inputs by comparator B. The LED load is powered from energy stored in the output capacitor during the inductor charging cycle. Once the peak inductor current value is achieved, the NDRV output is turned off (off-time is typically 300ns) allowing a portion of the energy stored in the inductor to be delivered to the load (e.g., see Figure 5, channel 2). This causes the output voltage to continue to rise across RSET at the input to the feedback circuit. The LX1992 continues to switch until the voltage at the FB pin exceeds the control voltage at the ADJ pin. The value of RSET is established by dividing the maximum adjust voltage by the maximum series LED current. A minimum value of 15Ω is recommended for RSET. The voltage at the FB pin is the product of IOUT (i.e., the current through the LED chain) and RSET. R SET INDUCTOR SELECTION AND OUTPUT CURRENT LIMIT PROGRAMMING Setting the level of peak inductor current to approximately 2X the expected maximum DC input current will minimize the inductor size, the input ripple current, and the output ripple voltage. The designer is encouraged to use inductors that will not saturate at the peak inductor current level. An inductor value of 47µH is recommended. Choosing a lower value emphasizes peak current overshoot while choosing a higher value emphasizes output ripple voltage. The peak switch current is defined using a resistor placed between the CS terminal and ground and the IPEAK equation is: I PEAK = I MIN + ⎛ ⎜ ⎝ VIN L ⎞ t + ⎛ ICS ⎟ D ⎜ R ⎞R CS ⎟ ⎠ ⎝ ICS ⎠ The maximum IPEAK value is limited by the ISRC value (max. = 0.8ARMS). The minimum IPEAK value is defined when RCS is zero. The value range for parameters IMIN and ICS are provided in the ELECTRICAL CHARACTERISTICS section of this data sheet. The parameter tD is related to internal operation of the device. A typical value at 25oC is 800ns. RICS is the internal current sense resistor connected to the SRC pin. A typical value at 25oC is 200mΩ. All of these parameters have an effect on the final IPEAK value. DESIGN EXAMPLE: Determine IPEAK where VIN equals 3.0V and RCS equals 4.02KΩ using nominal values for all other parameters. ⎞ × 800ns+ ⎛ 5.0µA ⎞ × 4.02KΩ IPEAK = 73mA + ⎛ 3.0V ⎜ ⎜ 47µH⎟ 200m ⎟ Ω⎠ ⎝ ⎠ ⎝ V ⎤ = ⎡ ADJmax ⎢ ILEDmax⎥ ⎣ ⎦ The result of this example yields a nominal IPEAK of approximately 225mA. OUTPUT RIPPLE AND CAPACITOR SELECTION The application of an external voltage source at the ADJ pin provides for output current adjustment over the entire dimming range and the designer can select one of two possible methods. The first option is to connect a PWM logic signal to the ADJ pin (e.g., see Figure 1). The LX1992 includes an internal 50pF capacitor to ground that works with an external resistor to create a low-pass filter (i.e., filter out the AC component of a pulse width modulated input of fPWM ≥ 100KHz). The second option is to adjust the reference voltage directly at the ADJ pin by applying a DC voltage from 0.0 to 0.3V (e.g., see Figure 2). The adjustment voltage level is selectable (with limited accuracy) by implementing the voltage divider created between the external series resistor and the internal 2.5MΩ resistor. Disabling the LX1992 is achieved by driving the SHDN pin with a low-level logic signal thus reducing the device power consumption to less than 0.5µA (typ). Copyright © 2000 Rev. 1.1b, 2005-03-03 Output voltage ripple is a function of the inductor value (L), the output capacitor value (COUT), the peak switch current setting (IPEAK), the load current (IOUT), the input voltage (VIN) and the output voltage (VOUT) for a this boost converter regulation scheme. When the switch is first turned on, the peak-to-peak voltage ripple is a function of the output droop (as the inductor current charges to IPEAK), the feedback transition error (i.e., typically 10mV), and the output overshoot (when the stored energy in the inductor is delivered to the load at the end of the charging cycle). Therefore the total ripple voltage is VRIPPLE = ∆VDROOP + ∆VOVERSHOOT + 10mV The initial droop can be estimated as follows where the 0.5 value in the denominator is an estimate of the voltage drop across the inductor and the FET’s RDS_ON: The Page 5 APPLICATION APPLICATION Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET APPLICATION INFORMATION W WW . Microsemi . C OM formula for ∆VDROOP is: PCB LAYOUT ∆VDROOP ⎛L⎞ ⎜ ⎟ × (I PK × I OUT ) ⎜C ⎟ ⎝ OUT ⎠ = (VIN − 0.5) The output overshoot can be estimated as follows where the 0.5 value in the denominator is an estimate of the voltage drop across the diode: 1 ∆VOVERSHOOT = 2×⎜ ⎛L⎞ ⎜ ⎟ × (I PK − IOUT )2 ⎟ ⎝ COUT ⎠ (VOUT + 0.5 − VIN ) The LX1992 produces high slew-rate voltage and current waveforms hence; the designer should take this into consideration when laying out the circuit. Minimizing trace lengths from the IC to the inductor, transistor, diode, input and output capacitors, and feedback connection (i.e., pin 6) are typical considerations. Moreover, the designer should maximize the DC input and output trace widths to accommodate peak current levels associated with this topology. EVALUATION BOARD DESIGN EXAMPLE: Determine the VRIPPLE where IPK equals 200mA, IOUT equals 12.8mA, L equals 47µH, COUT equals 4.7µF, VIN equals 3.0V, and VOUT equals 13.0V: ⎛ 47µH ⎞ ⎜ ⎟ ⎜ 4.7µF ⎟ × (200mA × 12.8mA ) ⎠ ≅ 10.2mV =⎝ (3.0 − 0.5) 1 2×⎜ ⎜ ∆VDROOP ∆VOVERSHOOT = ⎛ 47µH ⎞ ⎟ × (200mA − 12.8mA )2 ⎟ ⎝ 4.7µF ⎠ ≅ 18.4mV (13.0 + 0.5 − 3.0) Therefore, VRIPPLE = 10.2mV + 18.4mV + 10mV = 38.6mV 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 negative voltage transition that is greater than VOUT. TRANSISTOR SELECTION The LX1992 can source up to 100mA of gate current. An N-channel MOSFET with a relatively low threshold voltage, low gate charge and low RDS(ON) is required to optimize overall circuit performance. The LXE1992 Evaluation Board uses a Fairchild FDV303. This NMOS device was chosen because it demonstrates an RDS_ON of 0.33Ω and a total gate charge Qg of 1.64nC (typ.) The LXE1992 evaluation board is available from Microsemi for assessing overall circuit performance. The evaluation board, shown in Figure 3, is 3 by 3 inches (i.e., 7.6 by 7.6cm) square and programmed to drive 4 LEDs (provided). Designers can easily modify circuit parameters to suit their particular application by replacing RCS (as described in this section) RSET (i.e., R4) and diode load. Moreover, the inductor, FET, and switching diode are easily swapped out to promote design verification of a circuit that maximizes efficiency and minimizes cost for a specific application. The evaluation board input and output connections are described in Table 1. The DC input voltage is applied to VBAT (not VCC) however the LX1992 IC may be driven from a separate DC source via the VCC input. The output current (i.e., LED brightness) is controlled by adjusting the on-board potentiometer. The designer may elect to drive the brightness adjustment circuit from VBAT or via a separate voltage source by selecting the appropriate jumper position (see Table 2). Optional external adjustment of the output LED current is achieved by disengaging the potentiometer and applying either a DC voltage or a PWM-type signal to the VADJ input. The PWM signal frequency should be higher than 150KHz and contain a DC component les than 350mV. The LX1992 exhibits a low quiescent current (IQ < 0.5µA: typ) during shutdown mode. The SHDN pin is used to exercise the shutdown function on the evaluation board. This pin is pulled-up to VCC via a 10KΩ resistor. Grounding the SHDN pin shuts down the IC (not the circuit output). The output voltage (i.e., voltage across the LED string) is readily measured at the VOUT terminal and LED current is derived from measuring the voltage at the VFDBK pin and dividing this value by 15Ω (i.e., R4). The factory installed component list for this must-have design tool is provided in Table 3 and the schematic is shown in Figure 4 APPLICATION APPLICATION Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET APPLICATION INFORMATION (CONTINUED) W WW . Microsemi . C OM Figure 5: LXE1992 Engineering Evaluation Board Table 1: Input and Ouput Pin Assignments Pin Name VBAT VCC VPOT VADJ IN /SHDN VOUT VFDBK Allowable Range 0 to 6V 1.6V to 6V 1.6V to 6V 0 to 350mV 0 to VCC 0 to 18V 0 to 400mv Description Main power supply for output. (Set external current limit to 0.5A) LX1992 power. May be strapped to VBAT or use a separate supply if VCC jumper is in the SEP position. Do not power output from VCC pin on board.. Potentiometer power. May be strapped to VBAT or use a separate supply if VPOT jumper is in the SEP position. Do not power output from VPOT pin on board. Apply a DC voltage or a PWM voltage to this pin to adjust the LED current. PWM inputs should be greater than 120Hz and DC portion less than 350mV. Pulled up to VCC on board (10KΩ), Ground to inhibit the LX1992. Power supply output voltage that is applied to LED string. Sense resistor voltage. Divide this voltage by 15 to determine LED current. Table 2: Jumper Pin Position Assignments Jumper Position VCC/ BAT VCC/ SEP VPOT/ VBAT VPOT/ SEP ADJ/ POT ADJ/ EXT Functional Description Use this position when powering VBAT and VCC from the same supply. Do not connect power to the VCC input when using this jumper position. Use this position when using a separate VCC supply (different from VBAT). Use this position when powering the potentiometer reference circuit from the VBAT supply. Do not connect power to the VCC input when using this jumper position. Use this position when using a separate power supply (different from VBAT) to power the potentiometer reference circuit. This will lower the VBAT current and provide a more accurate efficiency reading for the LX1992 circuit. Use this position when using the potentiometer to adjust LED current. Use this position when adjusting the LED current with an external PWM that has a repetition rate >120Hz. Or when using a DC adjustment voltage. APPLICATION APPLICATION Note: Always put jumpers in one of the two possible positions Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET APPLICATION INFORMATION (CONTINUED) W WW . Microsemi . C OM Table 3: Factory Installed Component List for the LX1992 Evaluation Board Quantity 1 1 1 2 2 1 1 1 2 1 1 1 1 4 3 3 Part Reference Q1 CR1 L1 C1, C2 C3, C4 R4 R5 R2 R3, R6 R1 R7 VR1 VR2 LED1 - 4 JB1 - JB3 Description Mosfet, N-Channel, 25V, SOT23 Type SMT Rectifier, Schottky, 1A, 20V, Powermite Type SMT Inductor, 47uH, 540mA, SMT Capacitor, Ceramic X5R, 4.7uF, 25V, 1210 Type SMT Capacitor, Ceramic X7R, 0.1uF, 50V, 0805 Type SMT Resistor, 15 Ohm, 1/10W, 0805 Type SMT Resistor, 1K, 1/16W, 0603 Type SMT Resistor, 4.02K, 1/16W, 0603 Type SMT Resistor, 100K, 1/16W, 0603 Type SMT Resistor, 10K, 1/16W, 0603 Type SMT Trimpot, 50K, 1/2W, Through Hole Type IC, Voltage Reference, 1.25 Volts, SOT23 Type SMT Diode, Zener, 24V, 3W Powermite Type SMT White LED Header, 3 Pos Vertical Type Jumper Manufacturer Fairchild Microsemi Toko Taiyo Yuden Murata Panasonic Panasonic Panasonic Panasonic Panasonic Bourns Microsemi Microsemi Chicago Miniature 3M 3M Part Number FDV303N UPS5817 A920CY-470 CETMK325BJ475MN GRM40X7R104M050 ERJ6ENF15R0 ERJ3EKF1001 ERJ3EKF4021 ERJ3EKF1003 ERJ3EKF1002 3352E-1-503 LX432CSC 1PMT5934B CMD333UWC 929647-09-36 929955-06 Note: The minimum set of parts needed to build a working power supply are: Q1, CR1, L1, C2, C3, R2, R4, U1. L1 47µH CR1 UPS5817 V BAT VPOT VCC C1 4.7µF 25V Q1 FDV303N C3 0.1µF 50V CMD333UW C SR C GN D CS R2 4.02k AD J NDR V IN CMD333U W C FB SHDN CMD333UW C VR2 20V 1W 1PMT4114 C2 4.7µF 25V GND VOUT VCC R1 10k SHDN CMD333UW C R3 100k R4 15 Ω VADJ VADJ R5 1k VFDBK APPLICATION APPLICATION VPOT R6 100k C4 0.1µF 25V VR1 LX432 R7 50k Figure 4 – LXE1992 Boost Evaluation Board Schematic Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET CHARACTERISTIC CURVES W WW . Microsemi . C OM Figure 5: VOUT and Inductor Current Waveforms. Channel 1: VOUT (AC coupled; 200mV/div) Channel 2: Inductor Current (100mA/div.) Configuration: VIN = 3.0V, VOUT = 13.0V, IIN = 65mA Figure 6: VOUT and Inductor Current Waveforms. Channel 1: VOUT (AC coupled; 100mV/div) Channel 2: Inductor Current (100mA/div.) Configuration: VIN = 3.0V, VOUT = 13.7V, IIN = 120mA 90% 5 4 3 2 1 0 0 20 40 60 80 100 Driv e Current (mA) 120 140 160 Efficiency 80% Drive Voltage (V) 70% 60% 50% 0 2 4 6 8 10 LED Current (mA) 12 14 16 18 Figure 7: Gate Drive Voltage vs. Drive Current at T = 25oC. 100% Figure 8: Efficiency vs. LED Output Current. Configuration: VIN = 3.0V, L = 47µH, RCS = 4KΩ Note: Data taken from LXE1992 Evaluation Board 90% Efficiency 80% 70% 60% 50% 0 2 4 6 8 10 12 14 16 LED Current (mA) 18 20 22 24 Efficiency Measurement Hint: When doing an efficiency evaluation using the LX1992 Evaluation Board, VPOT should be driven by a separate voltage supply to account for losses associated with the onboard reference (i.e., the 1.25V shunt regulator and 1KΩ resistor). This circuit will have VBAT 1.25V across it and at the higher input voltages the 1KΩ resistor could have as much as 4mA through it. This shunt regulator circuitry will adversely effect the overall efficiency measurement and is not normally used in an application. Therefore it should not be considered when measuring efficiency. CHARTS CH A R T S Figure 9: Efficiency vs. LED Output Current. Configuration: VIN = 5.0V, L = 47µH, RCS = 4KΩ Note: Data taken from LXE1992 Evaluation Board Copyright © 2000 Rev. 1.1b, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET PACKAGE DIMENSIONS W WW . Microsemi . C OM DU 8-Pin Miniature Shrink Outline Package (MSOP) A Dim A B C D G H J K L M N P B H G P C N L K M D MILLIMETERS MIN MAX 2.85 3.05 2.90 3.10 – 1.10 0.25 0.40 0.65 BSC 0.38 0.64 0.13 0.18 0.95 BSC 0.40 0.70 3° 0.05 0.15 4.75 5.05 INCHES MIN MAX .112 .120 .114 .122 – 0.043 0.009 0.160 0.025 BSC 0.015 0.025 0.005 0.007 0.037 BSC 0.016 0.027 3° 0.002 0.006 0.187 0.198 LM 8-Pin Plastic MLP-Micro Exposed Pad Dim D L2 K E D2 E2 L2 Θ L e b A2 A3 A A1 Internally Connected together, but isolated from all other terminals A A1 A2 A3 b D E e D2 E2 K L L2 Θ Note: MILLIMETERS MIN MAX 0.80 1.00 0.00 0.05 0.65 0.75 0.15 0.25 0.28 0.38 2.90 3.10 2.90 3.10 0.65 BSC 1.52 2.08 1.02 1.31 0.20 * 0.20 0.60 0 0.13 0° 12° INCHES MIN MAX 0.031 0.039 0.000 0.002 0.025 0.029 0.005 0.009 0.011 0.015 0.114 0.122 0.114 0.122 0.025 BSC 0.060 0.082 0.040 0.052 0.008 * 0.008 0.023 0 0.005 0° 12° MECHANICALS MECHANICALS 1. 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, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 LX1992 TM ® High Efficiency LED Driver P RODUCTION D ATA S HEET NOTES W WW . Microsemi . C OM NOTES 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, 2005-03-03 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 11