Four-String White LED Driver ADD5205 Data Sheet White LED driver based on inductive boost converter Input voltage range: 2.8 V to 18 V Internal compensation 1 MHz fixed operating frequency 28 V fixed overvoltage protection Built-in soft start for boost converter Drives up to 4 LED current sources LED current adjustable up to 25 mA for each channel DC current level brightness control with PWM input LED open fault protection General Thermal shutdown Undervoltage lockout 12-lead, 3 mm × 3 mm × 0.75 mm LFCSP package FUNCTIONAL BLOCK DIAGRAM STEP-UP SWITCHING REGULATOR 4-CHANNEL CURRENT SOURCES BRIGHTNESS CONTROL LOGIC UNDERVOLTAGE LOCKOUT SOFT START THERMAL PROTECTION OVERVOLTAGE PROTECTION AUTODISABLE FOR LED OPEN 09858-001 FEATURES Figure 1. APPLICATIONS Smart PCs, PMPs, tablet PCs, UMPCs, and notebooks GENERAL DESCRIPTION The ADD5205 is a white LED driver for backlight applications based on high efficiency, current mode, step-up converter technology. It is designed with a 0.3 Ω internal switch and 1 MHz fixed operating frequency. The ADD5205 contains four regulated constant current sources for uniform brightness intensity. Each current source is capable of driving up to 25 mA. The ADD5205 has four parallel strings of multiple series connected LEDs with ±2% current matching. The device provides adjustable current sources that drive up to 25 mA using an external resistor. The LED current can be controlled by a PWM signal input on the PWM pin. An internal circuit translates the PWM signal to an analog signal with an external capacitor and linearly controls the LED current. The ADD5205 has multiple safety protection features to prevent any damage during fault conditions. If one or more LEDs are open, the device disables the faulty current regulator automatically. The internal soft start prevents inrush current during startup. A thermal shutdown protection feature prevents thermal damage. The ADD5205 is available in a low profile, thermally enhanced 3 mm × 3 mm × 0.75 mm, 12-lead lead frame chip scale package (LFCSP) and is specified over the temperature range of −25°C to +85°C. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved. ADD5205 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characteristics ..............................................8 Applications....................................................................................... 1 Theory of Operation ...................................................................... 10 Functional Block Diagram .............................................................. 1 Current Mode, Stepup Switching Regulator Operation........ 10 General Description ......................................................................... 1 Current Source............................................................................ 10 Revision History ............................................................................... 2 PWM Dimming Mode .............................................................. 10 Functional Block Diagram .............................................................. 3 Safety Features ............................................................................ 10 Specifications..................................................................................... 4 External Component Selection Guide..................................... 11 Absolute Maximum Ratings............................................................ 6 Layout Guidelines....................................................................... 12 Thermal Resistance ...................................................................... 6 Typical Application Circuit ........................................................... 13 ESD Caution.................................................................................. 6 Outline Dimensions ....................................................................... 14 Pin Configuration and Function Descriptions............................. 7 Ordering Guide .......................................................................... 14 REVISION HISTORY 8/11—Revision 0: Initial Version Rev. 0 | Page 2 of 16 Data Sheet ADD5205 FUNCTIONAL BLOCK DIAGRAM VIN SHDN OVP 1 2 5 VOLTAGE REFERENCE THERMAL SHUTDOWN UVP REF REF OCP REF SHUTDOWN UVP COMP R1 LL COMP OVP REF LL REF ERROR AMP GM PWM COMP 4 SW 3 GND 12 FB1 11 FB2 10 FB3 9 FB4 R2 R Q RC S DCOMP DREF CC OSC + CURRENT SENSE + SOFT START HEADROOM CONTROL LED OPEN FAULT PROTECTION ISET 7 CURRENT SOURCE 1 VREF GENERATOR CURRENT SOURCE 2 PWM 6 RSENSE R_FILTER CURRENT SOURCE 3 C_FILTER 8 09858-003 CURRENT SOURCE 4 Figure 2. Functional Block Diagram Rev. 0 | Page 3 of 16 ADD5205 Data Sheet SPECIFICATIONS VIN = 3.7 V, SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Table 1. Parameter SUPPLY Input Voltage Range Quiescent Current Shutdown Supply Current SWITCH On Resistance Switch Current Limit Leakage Current OSCILLATOR Switching Frequency Maximum Duty Cycle SOFT START Soft Start Time 1 CURRENT SOURCE ISET Pin Voltage C_FILTER Pin Voltage Adjustable LED Current1 Constant Current Sink of 20 mA 2 Headroom Voltage of 20 mA2 Current Matching Between Strings2 LED Current Accuracy of 20 mA2 Current Source Leakage Current SHUTDOWN CONTROL SHDN Voltage High SHDN Voltage Low PWM Control PWM Input Frequency Range1 PWM Voltage High PWM Voltage Low 1 2 Symbol Test Conditions/Comments VIN IQ ISD VIN = 2.8 V to 18 V, not switching VIN = 2.8 V to 18 V, SHDN = 0 V 3.4 ISW = 100 mA 0.3 1.9 RDS(ON) ICL ILKG Min 2.8 fOSC DMAX VSET VC_FILTER ILED ILED20 VHR20 Typ Max Unit 18 1 V mA μA 1 Ω A μA 1 90 MHz % 1.5 ms 1.26 0.22 RSET = 130 kΩ RSET = 130 kΩ ILED = 20 mA ILED = 20 mA −2 −3 +2 +3 1 V V mA mA V % % μA VSHDN_HIGH VIN = 2.8 V to 18 V 1.5 6 V VSHDN_LOW VIN = 2.8 V to 18 V 0.6 V VPWM_HIGH VPWM_LOW VIN = 2.8 V to 18 V VIN = 2.8 V to 18 V 0.6 kHz V V Duty = 100% Guaranteed by design. Tested at TA = 25°C. Rev. 0 | Page 4 of 16 19.6 20 0.66 25 20.6 0.1 1.5 Data Sheet ADD5205 VIN = 3.7 V, SHDN = high, TA = −25°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C. Table 2. Parameter THERMAL PROTECTION Thermal Shutdown Threshold 1 Thermal Shutdown Hysteresis1 UVLO UVLO Rising Threshold UVLO Falling Threshold OVERVOLTAGE PROTECTION Overvoltage Threshold on OVP Pin 1 Symbol Test Conditions/Comments Min TSD TSDHYST VUVLOR VUVLOF VIN rising VIN falling VOVP 28 Guaranteed by design. Rev. 0 | Page 5 of 16 Typ Max Unit 160 30 °C °C 2.5 2 V V V ADD5205 Data Sheet ABSOLUTE MAXIMUM RATINGS TA = 25°C, unless otherwise noted. THERMAL RESISTANCE Table 3. θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Parameter VIN SW SHDN, ISET, C_FILTER PWM FB1, FB2, FB3, FB4 OVP Maximum Junction Temperature (TJ max) Operating Temperature Range (TA) Storage Temperature Range (TS) Reflow Peak Temperature (20 sec to 40 sec) Rating −0.3 V to +20 V −0.3 V to +32 V −0.3 V to +7 V −0.3 V to +3.6 V −0.3 V to +7 V −0.3 V to +32 V −0.3 V to +32 V 150°C −25°C to +85°C −65°C to +150°C 260°C Table 4. Thermal Resistance Package Type 12-Lead LFCSP ESD CAUTION Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. 0 | Page 6 of 16 θJA 41.6 θJC 7.65 Unit °C/W Data Sheet ADD5205 VIN 1 10 FB3 11 FB2 12 FB1 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS ADD5205 SHDN 2 TOP VIEW 8 C_FILTER NOTES 1. CONNECT THE EXPOSED PADDLE TO GROUND. 09858-002 PWM 6 (Not to Scale) SW 4 7 ISET OVP 5 GND 3 9 FB4 Figure 3. Pin Configuration Table 5. Pin Function Descriptions Pin No. 1 2 3 4 5 Mnemonic VIN SHDN GND SW OVP 6 7 8 PWM ISET C_FILTER 9 FB4 10 FB3 11 FB2 12 FB1 EPAD Description Supply Input Pin. Bypassed with a capacitor to ground. Shutdown Control Pin for Enabling IC. Active low. Ground Pin. Drain Connection of the Internal Power FET Pin. Overvoltage Protection Sense Input Pin. Must be locally bypassed with a 100 nF capacitor and placed as close as possible to the IC. PWM Signal Input Pin. Full-Scale LED Current Set Pin. A resistor from this pin to ground sets the LED current up to 25 mA. Filtered PWM Signal Output Pin. Connect a capacitor between C_FILTER and ground. This capacitor forms a low-pass filter with an internal resistor. Regulated Current Sink Input Pin. Connect the bottom cathode of the LED string to this pin. If unused, connect FB4 to ground. Regulated Current Sink Input Pin. Connect the bottom cathode of the LED string to this pin. If unused, connect FB3 to ground. Regulated Current Sink Input Pin. Connect the bottom cathode of the LED string to this pin. If unused, connect FB2 to ground. Regulated Current Sink Input Pin. Connect the bottom cathode of the LED string to this pin. This channel should be connected to LEDs as a default channel. Connect the exposed paddle to ground. Rev. 0 | Page 7 of 16 ADD5205 Data Sheet TYPICAL PERFORMANCE CHARACTERISTICS 25 90 20 80 LED CURRENT (mA) 70 60 50 40 30 15 10 5 20 0 0 5 10 INPUT VOLTAGE (V) 15 20 0 0 Figure 4. Boost Converter Efficiency vs. Input Voltage, ILED = 20 mA, Brightness = 100%, and LEDs = 6 Series × 4 Parallel 10 INPUT VOLTAGE (V) 15 20 Figure 7. LED Current vs. Input Voltage (ILED = 22 mA) 30 20 15 LED CURRENT MATCHING (%) 25 20 15 10 5 10 5 0 –5 –10 –15 0 200 400 600 800 1000 RSET (kΩ) 1400 1200 1600 –20 09858-005 0 0 20 60 40 PWM INPUT DUTY CYCLE (%) 80 100 Figure 8. LED Current Matching vs. PWM Input Duty Cycle Figure 5. LED Current (ILED) vs. RSET 20 VOUT (10V/DIV) 18 VSW (10V/DIV) 1 14 12 2 10 SHDN (3V/DIV) 8 IL (500mA/DIV) 3 6 4 0 0 20 40 60 80 PWM INPUT DUTY CYCLE (%) 100 VIN = 3.7V BRIGHTNESS = 100% Figure 6. LED Current vs. PWM Input Duty Cycle A CH3 6 SERIES x 4 PARALLEL 960mV Figure 9. Start-Up Waveforms (Brightness = 100%) Rev. 0 | Page 8 of 16 09858-009 4 2 09858-006 LED CURRENT (mA) 16 09858-008 LED CURRENT (mA) 5 09858-007 10 09858-004 BOOST CONVERTER EFFICIENCY (%) 100 Data Sheet ADD5205 PWM (2V/DIV) VOUT (100mV/DIV) 1 1 VSW (10V/DIV) VFB1 (1V/DIV) 2 2 IL (500mA/DIV) IFB1 (10mA/DIV) 4 A CH2 6 SERIES x 4 PARALLEL 11.6V VIN = 5V BRIGHTNESS = 10% A CH1 6 SERIES x 4 PARALLEL 840mV 09858-012 VIN = 18V BRIGHTNESS = 100% 09858-010 4 Figure 12. LED Current Waveforms (Brightness = 10%) Figure 10. Switching Waveforms (VIN = 18 V) PWM (2V/DIV) VOUT (100mV/DIV) 1 1 VSW (10V/DIV) VFB1 (1V/DIV) 2 2 IFB1 (10mA/DIV) IL (500mA/DIV) A CH2 6 SERIES x 4 PARALLEL 11.6V 09858-011 VIN = 3V BRIGHTNESS = 100% VIN = 5V BRIGHTNESS = 70% A CH1 6 SERIES x 4 PARALLEL 840mV Figure 13. LED FB1 Waveforms (Brightness = 70%) Figure 11. Switching Waveforms (VIN = 3 V) Rev. 0 | Page 9 of 16 09858-013 4 4 ADD5205 Data Sheet THEORY OF OPERATION PWM DIMMING MODE The ADD5205 uses a current mode PWM boost regulator to provide the minimal voltage needed to enable the LED string at the programmed LED current. The current mode regulation system allows fast transient response while maintaining a stable output voltage. The regulator response can be optimized for a wide range of input voltages, output voltages, and load conditions. The ADD5205 can provide a 28 V fixed overvoltage protection voltage and drive up to 6 LEDs (3.4 V/20 mA type of LEDs) for four channels from a supply of 3 V or up to 7 LEDs (3.4 V/20 mA type of LEDs) for four channels from a supply of 5 V to 18 V. The ADD5205 contains four current sources to provide accurate current sinking for each LED string. String-to-string tolerance is kept within ±2% at 20 mA. Each LED string current is adjusted up to 25 mA by an external resistor. The ADD5205 contains an LED open fault protection circuit for each channel. The ADD5205 recognizes that the current source has an open load fault for the current source, and the current source is disabled. Programming the LED Current As shown in Figure 2, the ADD5205 has an LED current set pin (ISET). A resistor (RSET) from this pin to ground adjusts the LED current up to 25 mA (see Figure 15). LED current level can be set by 2600 ( A) RSET DC Current Dimming In this mode, the maximum LED current is set by the value of RSET. Once the maximum LED current is set, the LED current can be changed through PWM input. DUTY = 80% DUTY = 60% DUTY = 40% DUTY = 20% PWMI ILED MAX CURRENT SOURCE ILED = The ADD5205 supports PWM input. The internal resistor and external capacitor change the PWM input duty to analog level, and the low-pass filter output adjusts each current source sink current level. ILED 0.8 × ILED MAX 0.6 × ILED MAX 0.4 × ILED MAX 0A 0.2 × ILED MAX 09858-014 CURRENT MODE, STEPUP SWITCHING REGULATOR OPERATION Figure 14. DC Current Dimming Timing SAFETY FEATURES The ADD5205 contains several safety features to provide stable operation, such as soft start, open load protection (OLP), undervoltage lockout (UVLO), and thermal protection. Soft Start The ADD5205 contains an internal soft start function to reduce inrush current at startup. The soft start time is typically 1.5 ms. OLP The ADD5205 contains a headroom control circuit to minimize power loss at each current source. Therefore, the minimum feedback voltage is achieved by regulating the output voltage of the boost converter. If any LED string is open during normal operation, the current source headroom voltage (VHR) is pulled to GND. In this condition, OLP is activated. UVLO An undervoltage lockout circuit is included with built-in hysteresis. The ADD5205 turns on when VIN rises above 2.5 V (typical) and shuts down when VIN falls below 2 V (typical). Thermal Protection Thermal overload protection prevents excessive power dissipation from overheating the ADD5205. When the junction temperature (TJ) exceeds 160°C, a thermal sensor immediately activates the fault protection, which shuts down the device, allowing the IC to cool. The device self starts when the TJ of the die falls below 130°C. Rev. 0 | Page 10 of 16 Data Sheet ADD5205 EXTERNAL COMPONENT SELECTION GUIDE Table 6 shows a list of recommend inductors. Inductor Selection Table 6. Recommended Inductors The inductor is an integral part of the step-up converter. It stores energy during the switch-on time and transfers that energy to the output through the output diode during the switch-off time. An inductor in the 3.3 μH to 6.8 μH range is recommended. In general, lower inductance values result in higher saturation current and lower series resistance for a given physical size. Coilcraft Part No. XFL4020-332ML LPS4012-472ML LPS4018-472ML LPS4018-682ML The input (VIN) and output (VOUT) voltages determine the switch duty cycle (D), which in turn can be used to determine the inductor ripple current. Input and Output Capacitors Selection D= VOUT − VIN VOUT Use the duty cycle and switching frequency (fSW) to determine the on time (tON). t ON D = f SW The inductor ripple current (ΔIL) in a steady state is ΔI L = VIN × t ON L VIN × t ON ΔI L I LAVG = ΔI L = I OUT × VOUT η × VIN Size (mm) 4×4×2 3.9 × 3.9 × 1.1 3.9 × 3.9 × 1.7 3.9 × 3.9 × 1.7 The ADD5205 requires input and output bypass capacitors to supply transient currents while maintaining a constant input and output voltage. Use a low effective series resistance (ESR) 4.7 μF or greater capacitor for the input capacitor to prevent noise at the ADD5205 input. Place the input between VIN and GND, as close as possible to the ADD5205. The output capacitor maintains the output voltage and supplies current to the load while the ADD5205 switch is on. The value and characteristics of the output capacitor greatly affect the output voltage ripple and stability of the regulator. Use a ceramic X5R or X7R dielectric capacitor, and for the output capacitor, a 4.7 μF or greater capacitor is preferred. Diode Selection Ensure that the peak inductor current (that is, the maximum input current plus half of the inductor ripple current) is less than the rated saturation current of the inductor. In addition, ensure that the maximum rated rms current of the inductor is greater than the maximum dc input current to the regulator. 1 I LPK = I LAVG + ΔI L , 2 ISAT (A) 2.7 1.6 1.8 1.2 Place a 100 nF or greater capacitor as close as possible to the OVP pin of ADD5205. Solve for the inductance value (L). L= L (μH) 3.3 4.7 4.7 6.8 The output diode conducts the inductor current to the output capacitor and loads while the switch is off. For high efficiency, minimize the forward voltage drop of the diode. Schottky diodes are recommended. The output diode for a boost regulator must be chosen depending on the output voltage and the output current. The diode must be rated for a reverse voltage greater than the output voltage used. The average current rating must be greater than the maximum load current expected, and the peak current rating must be greater than the peak inductor current. V − VIN 1 VIN OUT L f SW × VOUT where: ILPK is the peak inductor current. ILAVG is the input average current. Rev. 0 | Page 11 of 16 ADD5205 Data Sheet LAYOUT GUIDELINES Layout Procedure When designing a high frequency, switching, regulated power supply, layout is very important. Using a good layout can solve many problems associated with these types of supplies. The main problems are loss of regulation at high output current and/or large input-to-output voltage differentials, excessive noise on the output and switch waveforms, and instability. Using the following guidelines can help minimize these problems. Use the following general guidelines when designing PCBs: Make all power (high current) traces as short, direct, and thick as possible. It is good practice on a standard printed circuit board (PCB) to make the traces an absolute minimum of 15 mil (0.381 mm) per ampere. Place the inductor, output capacitors, and output diode as close to each other as possible. This helps reduce the EMI radiated by the power traces that is due to the high switching currents through them. This also reduces lead inductance and resistance, which in turn reduces noise spikes, ringing, and resistive losses that produce voltage errors. The grounds of the IC, input capacitors, output capacitors, and output diode (if applicable), should be connected close together, directly to a ground plane. It is also a good idea to have a ground plane on both sides of the PCB. This reduces noise by reducing ground loop errors and by absorbing more of the EMI radiated by the inductor. • • • • • • • • Keep CIN close to the VIN and GND leads of the ADD5205. Keep the high current path from CIN (through L1) to the SW and GND leads as short as possible. Keep the high current path from CIN (through L1), D1, and COUT as short as possible. Keep high current traces as short and wide as possible. Place the COVP as close as possible to the OVP pin. Place the LED current setting resistors as close as possible to each pin to prevent noise pickup. Avoid routing noise sensitive traces near high current traces and components, especially the LED current setting node (ISET). Use a thermal pad size that is the same dimension as the exposed pad on the bottom of the package. Heat Sinking When using a surface-mount power IC or external power switches, the PCB can often be used as the heat sink. This is done by using the copper area of the PCB to transfer heat from the device. Users should maximize this area to optimize thermal performance. Due to how switching regulators operate, there are two power states: on and off. During each state, there is a current loop made by the power components currently conducting. Place the power components so that the current loop is conducting in the same direction during each of the two states. This prevents magnetic field reversal caused by the traces between the two half cycles and reduces radiated EMI. Rev. 0 | Page 12 of 16 Data Sheet ADD5205 TYPICAL APPLICATION CIRCUIT L1 4.7µH CIN 4.7µF 1 VIN 2 SHDN 6 PWM 8 C_FILTER ON OFF CFILTER 1µF COUT 4.7µF 4 SW OVP 5 COVP 100nF ADD5205 FB1 12 FB2 11 FB3 10 FB4 9 GND ISET 3 7 RSET Figure 15. Typical Application Circuit Rev. 0 | Page 13 of 16 09858-015 + – D1 ADD5205 Data Sheet OUTLINE DIMENSIONS PIN 1 INDICATOR 0.30 0.23 0.18 10 0.50 BSC 1 9 EXPOSED PAD 1.70 1.60 SQ 1.50 7 TOP VIEW 0.80 0.75 0.70 0.50 0.40 0.30 3 6 4 0.20 MIN BOTTOM VIEW 0.05 MAX 0.02 NOM COPLANARITY 0.08 0.20 REF SEATING PLANE PIN 1 INDICATOR 12 FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. COMPLIANT TO JEDEC STANDARDS MO-229-WEED-4. 072809-B 3.10 3.00 SQ 2.90 Figure 16. 12-Lead Lead Frame Chip Scale Package [LFCSP_WQ] 3 mm × 3 mm Body, Very Very Thin Quad (CP-12-6) Dimensions shown in millimeters ORDERING GUIDE Model 1 ADD5205ACPZ-RL 1 Temperature Range −25°C to +85°C Package Description 12-Lead Lead Frame Chip Scale Package [LFCSP_WQ] Z = RoHS Compliant Part. Rev. 0 | Page 14 of 16 Package Option CP-12-6 Data Sheet ADD5205 NOTES Rev. 0 | Page 15 of 16 ADD5205 Data Sheet NOTES ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D09858-0-8/11(0) Rev. 0 | Page 16 of 16