LX1995-1CSE-TR

LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET DESCRIPTION KEY FEATURES < 1µA Shutdown Current > 85% Maximum Efficiency Efficient at Low Current Levels < 70µA Quiescent Supply Current in Operating Mode VIN Range 1.6V to 5.5V Logic Controlled Shutdown Dimming Options: PWM or Varying DC Voltage Tiny 5-Pin TSOT Package Smallest External Components APPLICATIONS The Microsemi LX1995-x is a miniature LED driver with integrated drivers. It is designed to drive white or color LEDs in portable display applications. The LX1995-x is an adjustable step-up boost converter. The LX1995-x can switch up to 2MHz allowing designers to use a low cost, small inductor and filter capacitor. The driver supports a wide input voltage range (1.6V to 5.5V) with efficiency greater than 85% and can start up at 1.6V input. The LX1995-x is a low cost, high efficiency LED driver. The design is based on a pseudo-hysteretic pulse frequency modulation topology. In portable battery applications the LX1995-x offers high system efficiency with low quiescent current: in operation IQ is < 70µA and in standby IQ is < 1µA. The LX1995-x output current is programmable using an external current sense resistor in series with LEDs. This configuration provides a feedback to the FB pin which maintains constant output current independent of input voltage and LED forward voltage (VF). LED dimming is accomplished using a PWM signal or varying DC voltage methods. The LX1995-x is available in the 5Pin TSOT and SOT-23 package. The LX1995-1 can drive up to 6 LEDs (switching current is 325mA). The LX1995-2 can drive up to 10 LEDs (switching current is 500mA). WWW . Microsemi . C OM Pagers Wireless Phones PDAs LED Driver Digital Camera Displays GPS Receivers IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT VBAT = 2.0V to 5.0V IN SW LX1995 ON OFF SHDN GND FB LX1995 LX1995 PACKAGE ORDER INFO TA (°C) -40 to 85 -40 to 85 Switch Current 325mA 500mA SG Plastic TSOT 5-Pin RoHS Compliant / Pb-free SE Plastic SOT-23 5-Pin LX1995-1CSE LX1995-2CSE RoHS Compliant / Pb-free Transition DC: 0503 LX1995-1CSG LX1995-2CSG Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1995-1CSG-TR) Copyright © 2000 Rev. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT WWW . Microsemi . C OM Supply Input Voltage ........................................................................-0.3V to 7.0V Feedback Peak Pulse Input Voltage (VFB) ..............................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN ) ...........................................-0.3V to VIN + 0.3V Switch Voltage (VSW) ........................................................................-0.3V to 30V Switch Current (ISW) ...................................................................................500mA Operating Temperature Range .........................................................-40°C to 85°C Maximum Operating Junction Temperature ................................................ 125°C Storage Temperature Range...........................................................-65°C to 150°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. SW 1 5 IN GND 2 FB 3 4 SHDN SG PACKAGE (Top View) SW GND 1 2 5 IN THERMAL DATA FB 3 4 SHDN SG SE Plastic TSOT 5-Pin 207°C/W SE PACKAGE (Top View) THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA RoHS / Pb-free 100% Matte Tin Lead Finish Plastic SOT-23 5-Pin 191°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. FUNCTIONAL PIN DESCRIPTION Name SW GND FB Description Inductor Switching Connection – Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. Common terminal for ground reference. Feedback Input – Connect to a current sense resistor between the load and GND to set the maximum output current. FB pin is regulated to 320mV. Active-Low Shutdown Input – A logic low shuts down the device and reduces the supply current to 10kHz VPWM = 3.3V DC = 10% to 90% ILED = 0mA to 20mA 4 9.09k Ω 3 90.9kΩ R 0.1µF C2 R 2 11.2k Ω R 1 15 Ω R Figure 4 – PWM to Analog Voltage Dimming LED Driver Application L1 VBAT = 2.0V to 5.0V 10µH 1206 Case Size SW IN C1 .1µF On Off LX1995 FB SHDN GND 320mV 2R - RA VCC RA RCS 2R R RA = (0.64 x R) / VCC LSB VCC MSB APPLICATIONS APPLICATIONS MSB 1 1 0 0 LSB 1 0 1 0 ILED 0.25 x IMAX 0.50 x IMAX 0.75 x IMAX IMAX Rcs = (0.32 x R) / {[R - (0.375 x RA)] x IMAX} Figure 5 – Binary Dimming LED Driver Application 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. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET THEORY OF OPERATION WWW . Microsemi . C OM OPERATING THEORY The LX1995-x is a PFM boost converter optimized for driving a series of white or color LEDs. It operates in a pseudo-hysteretic mode with a fixed, 300ns, switch “off time”. When the LX1995-x enables, the LED current decreases causing the FB voltage to decrease to a value less than 320mV. The feedback comparator (See Simplified Block Diagram) activates the control logic. The control logic turns on the DRV output circuit that connects to the internal N-Channel MOSFET gate. The switch output (SW) is switched “on” and remains “on” until the inductor current ramps up to the peak current level (typically 325mA for LX1995-1). 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 output is turned off and the energy stored in the inductor delivers to the load. This causes the voltage to rise across the current setting resistor (R1) at the input to the feedback circuit. The LX1995-x continues to switch until the voltage at the FB pin exceeds 320mV. The value of R1 is calculated by dividing 320mV by the maximum series LED current. A minimum value of 3.3Ω is recommended for RSET. The voltage at the FB pin is the product of the LED current (ILED) and R1. R1 = 320mV I LED( MAX) INDUCTOR SELECTION AND OUTPUT CURRENT LIMIT PROGRAMMING Microsemi recommends the use inductors (for the LX1995-1) in the range of 10µH to 47µH due to saturation of peak inductor current. By increasing the average inductor current, the LX1995-x will extend the power range. Smaller inductor values will reduce output voltage ripple and are smaller in size. OUTPUT RIPPLE AND CAPACITOR SELECTION Output voltage ripple is depended on the selection of the inductor value (L), output capacitor value (COUT), peak switch current (IPEAK), load current (IOUT), input voltage (VIN) and the output voltage (VOUT). 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 (energy stored in the inductor). When the switch is first turn on, the total ripple voltage is: VRIPPLE = ∆VDROOP + ∆VOVERSHOOT+ 10mV eq. 3 The initial droop can be estimated with the assumption of 0.5V of voltage drop across the inductor and FET RDSON. eq. 1 ⎛L⎞ ⎜ ⎜ C ⎟ ⋅ (IPK × ILED ) ⎟ ∆VDROOP = ⎝ OUT ⎠ VIN − 0.5 eq. 4 DIMMING METHODS LX1995-x supports two dimming methods: PWM or DC Voltage. PWM mode: Connect system PWM logic signal to the SHDN pin (See Figure 1). This turns the LX1995-X on and off which pulses the LED current between zero and the setting determined by R1. DC Voltage mode: The designer can apply an adjustable DC voltage supply to the FB pin. As the DC voltage increases, the LED current decreases. The equation (see Figure 3) is: I LED = ⎛ R2 + R3 ⎞ ⎛ R ⎞⎤ 1⎡ ⎟ − VADJ ⋅ ⎜ 2 ⎟⎥ ⎢320mV ⋅ ⎜ ⎜R ⎟ ⎜R ⎟ R1 ⎢ 3 ⎝ ⎠ ⎝ 3 ⎠⎥ ⎣ ⎦ The output overshoot calculated with 0.5V as voltage drop across the diode. 1⎛ L ⎞ 2 ⋅⎜ ⎜ C ⎟ ⋅ (IPK − ILED ) ⎟ 2 ∆VOVERSHOOT = ⎝ OUT ⎠ VOUT − VIN + 0.5 eq. 5 eq. 2 Once the output voltage ripple is determined for the selected components, the output capacitor can then be adjusted to meet the target ripple voltage requirements. The LX1995-x is targeted for LED driver applications; output voltage ripple is not a critical application requirement. APPLICATIONS APPLICATIONS Copyright © 2000 Rev. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET LX1995-1 EFFICIENCY LX1995-2 EFFICIENCY 100 90 100 90 WWW . Microsemi . C OM Efficiency 80 5.0V IN Efficiency 80 70 60 5.0V IN 3.5V IN 70 60 47µH Inductor, 4 White LEDs 50 2 4 6 8 10 12 14 16 3.5V IN 47µH Inductor, 4 White LEDs 50 18 20 2 4 6 8 10 12 14 16 18 20 LED Current LED Current C CHARTS Copyright © 2000 Rev. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET PACKAGE DIMENSIONS WWW . Microsemi . C OM SG 5-Pin Thin Shrink Small Outline Package (TSOT) e 3 2 1 E E1 4 b e1 5 D A A2 A1 L2 Dim A A1 A2 b C D E E1 e L L2 MILLIMETERS MIN MAX 1.00 0.01 0.10 0.84 0.90 0.30 0.45 0.12 0.20 2.90 BSC 2.80 BSC 1.60 BSC 0.95 BSC 0.30 0.40 0.25 BSC INCHES MIN MAX 0.039 0.0004 0.004 0.033 0.035 0.012 0.018 0.005 0.008 0.114 BSC 0.110 BSC 0.063 BSC 0.037 BSC 0.012 0.016 0.010 BSC C L SE 5-Pin Small Outline Package (SOT-23) D G H E A1 A C B F J I K Dim A A1 B C D E F G H I J K MILLIMETERS MIN MAX 0.90 1.30 0.90 1.45 0.25 0.50 0.09 0.20 2.80 3.10 1.50 1.75 0.95 BSC 1.90 BSC 2.60 3.00 0.35 0.55 0.00 0.15 10° MAX INCHES MIN MAX 0.035 0.051 0.035 0.057 0.010 0.020 0.004 0.008 0.110 0.122 0.059 0.069 0.038 BSC 0.075 BSC 0.102 0.118 0.014 0.022 0.000 0.006 10° MAX M MECHANICALS 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. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 LX1995 TM ® Miniature LED Driver P RODUCTION D ATA S HEET NOTES WWW . 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. 1.1, 2005-07-07 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9