® RT8510A 43V 4-Channel LED Driver General Description Features The RT8510A is a high efficiency driver for white LEDs. It is designed for LCD panels that employ an array of LEDs as the lighting source. An integrated switch current mode Boost controller drives four strings in parallel and supports up to 12 pieces of LED per string. The internal current sinks support a maximum of ±2% current mismatching for excellent brightness uniformity in each string of LED. To provide enough headroom for current sink operation the Boost controller monitors the minimum voltage of feedback pins and regulates an optimized output voltage for power efficiency. z Wide Input Voltage : 4.2V to 24V z High Output Voltage : Up to 43V Adjustable Channel Current : 10mA to 80mA Channel Current Accuracy : ±3% Channel Current Matching : ±2% PWM Dimming Frequency : 120Hz to 30kHz Adjustable Switching Frequency : 500kHz to 2MHz Built-In Soft-Start Disconnect LED in Shutdown Open Current Sink Detection Adjustable Over-Voltage Protection Over-Temperature Protection Current Limit Protection Thin 28-Lead WQFN Package RoHS Compliant and Halogen Free z z z z z z z z z z The RT8510A has a wide input voltage range from 4.2V to 24V and provides an adjustable 10mA to 80mA LED current. The internal 200mΩ, 43V power switch with current-mode control provides cycle-by-cycle over-current protection. z z z Applications The RT8510A also integrates PWM dimming function for accurate LED current control. The input PWM dimming frequency can operate from 120Hz to 30kHz without inducing any inrush current through the LED or inductor. The switching frequency of the RT8510A is adjustable from 500kHz to 2MHz, allowing the flexibility between efficiency and component size. z z UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Marking Information A3= : Product Code A3=YM DNN YMDNN : Date Code The RT8510A is available in the WQFN-28L 4x5 package. Simplified Application Circuit VOUT D1 L VIN CIN R2 RT8510A VIN LX ROVP2 C2 COUT OVP EN Enable PWM Dimming C4 PWM COMP R3 C3 RRT RISET DS8510A-01 January 2014 : : : : : : : : CH1 CH2 CH3 ISET CH4 Copyright © 2014 Richtek Technology Corporation. All rights reserved. : : : : ROVP1 RT PGND : : : : AGND is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8510A Ordering Information Pin Configurations (TOP VIEW) RT8510A NC NC NC NC NC NC Package Type QW : WQFN-28L 4x5 (W-Type) 28 27 26 25 24 23 Lead Plating System G : Green (Halogen Free and Pb Free) VIN PWM EN LX LX PGND PGND OVP Note : Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. 22 2 21 3 20 4 19 GND 5 18 6 17 7 29 8 16 15 RT ISET COMP AGND CH4 CH3 CH2 CH1 9 10 11 12 13 14 Suitable for use in SnPb or Pb-free soldering processes. NC NC NC NC NC NC ` 1 WQFN-28L 4x5 Function Pin Description Pin No. Pin Name Pin Function 1 VIN Power Supply Input. 2 PWM Dimming Control Input. 3 EN Enable Control Input (Active High). Note that this pin is high impedance. There should be a 100kΩ pull-low resistor connected to GND when the control signal is floating. 4, 5 LX Switching Node of Boost Converter. 6, 7 PGND Power Ground of Boost Converter. OVP Sense Input for Over-Voltage Protection. The detecting threshold is 1.2V. 8 9, 10, 11, 12, 13, 14, 23, 24, 25, 26, NC 27, 28 15, 16, 17, 18 No Internal Connection. CH1 to CH 4 Current Sink for LED. Leave the pin unconnected if not used. 19 AGND Analog Ground of LED Driver. 20 COMP Compensation Node for Error Amplifier. Connect a compensation network to ground. 21 ISET LED Current Setting. LED current is set by the value of the resistor RISET connected from the ISET pin to ground. Do not short the ISET pin. VISET is typically 0.6V. ILED = 22 RT 29 (Exposed Pad) GND 95 RISET Switching Frequency Setting. This pin allows setting the switching frequency with a resistor to 500kHz to 2MHz. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A Function Block Diagram OVP LX EN VIN + 1.2 - RT OSC S Q R Q Regulator OCP OTP PWM Controller + PGND + EA - COMP VREF 4 LED Detection PWM CH1 CH2 CH3 CH4 + - - + : : + + 0.6V - - ISET AGND Operation OSC OVP The switching frequency is adjustable by the external resistor connected between the RT pin and GND. When OVP pin voltage is higher than 1.2V, the LX N-MOSFET is turned off immediately to protect the LX N-MOSFET. PWM Controller This controller includes some logic circuits to control LX N-MOSFET on/off. This block controls the minimum ontime and max duty of LX. OCP & OTP When LX N-MOSFET peak current is higher than 2.5A (typically), the LX N-MOSFET is turned off immediately and resumed again at next clock pulse. When the junction temperature is higher than 160°C (typically), the LX N-MOSFET turns off until the temperature is lower than the 130°C (typically). Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8510A-01 January 2014 LED Detection This block detects all LEDx voltage and selects a minimum voltage to EA (Error Amplifier). This function can guarantee the lowest of LED pin voltage is around 600mV when LED current is 20mA. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8510A Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Input Voltage, VIN to GND -----------------------------------------------------------------------------------EN, PWM, ISET, COMP, RT to GND -------------------------------------------------------------------------------LX, OVP, CH1, CH2, CH3, CH4 to GND ---------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-28L 4x5 ----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-28L 4x5, θJA -----------------------------------------------------------------------------------------------------WQFN-28L 4x5, θJC ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------------------MM (Machine Model) ---------------------------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 26.5V −0.3V to 26.5V −0.3V to 48V 3.57W 28°C/W 7°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 4.2V to 24V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 4.5V, TA = 25°C unless otherwise specified) Parameter Symbol Min Typ Max -- 1 1.5 2 3 -- -- 10 2 -- -- -- -- 0.8 120 -- 30k RRT = 25kΩ -- 2 -- RRT = 51kΩ -- 1 -- RRT = 102kΩ -- 0.5 -- LX On-Resistance (N-MOSFET) RDS(ON)_N VIN > 4.5V -- 0.2 -- Ω Minimum On-Time tON -- 120 -- ns Maximum Duty DMAX -- 92 -- % LX Current Limit ILIM -- 2.5 -- A VIN Quiescent Current IQ VIN Shutdown Current ISHDN Test Conditions VCOMP = 0V, No Switching VCOMP = 2V, Switching VIN = 4.5V, EN = 0V Unit mA μA Control Input EN, PWM Input Voltage Logic-High VIH Logic-Low VIL PWM Dimming Frequency VIN = 4.2V to 24V fPWM V Hz Boost Converter Switching Frequency fOSC VCOMP = 2V, Switching Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 MHz is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A Parameter Symbol Test Conditions Min Typ Max Unit LED Current Programming LED Current Matching ILEDM 2V > CHx > 0.4V Calculating (I(MAX) − I(AVG)) / I (AVG) x 100%, RISET = 4.75k -- -- ±2 % ISET Voltage VISET I LED = 20mA -- 0.6 -- V LED Current ICHx 2V > CHx > 0.4V, RISET = 4.75k 19.4 20 20.6 mA Fault Protection OVP Threshold VOVP -- 1.2 -- V OVP Fail Threshold VOVPF -- 50 -- mV Thermal Shutdown Temperature TSD -- 160 -- °C OTP Hysteresis T OTP_Hys -- 30 -- °C LED Pin Under-Voltage Threshold VLSD No Connection -- 50 -- mV -- 0.4 -- VCHx Highest Voltage LED String, RISET = 4.75k Highest Voltage LED String, RISET = 1.58k -- 0.8 -- Regulated VCHx V Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Guaranteed by design; not subject to production testing. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8510A-01 January 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8510A Typical Application Circuit VOUT 43V MAX L 10µH VIN 4.2V to 24V CIN 10µF R2 10 1 VIN RT8510A LX 4,5 C2 1µF OVP 3 EN Enable D1 C4 1nF R3 10k C3 10nF RRT 51k PGND 6,7 : : : : : : : : : : 4x10 LED String : : CH1 15 16 CH2 CH3 17 CH4 18 AGND 19 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 : : : : ROVP1 62k 2 PWM 20 COMP 22 RT 21 ISET RISET 4.75k COUT 10µF 8 100k PWM Dimming ROVP2 2M is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A Typical Operating Characteristics LED Current vs Input Voltage Efficiency vs. Input Voltage 25 100 90 23 LED Current (mA) Efficiency (%) 80 70 60 50 40 30 21 CH1 CH2 CH3 CH4 19 17 20 10 fOSC = 1MHz 40 LEDs, fOSC = 1MHz 15 0 4 8 12 16 20 24 4 9 14 Input Voltage (V) 24 Input Voltage (V) VISET vs. Temperature LED Current vs. Temperature 0.70 25 0.65 23 0.60 21 VISET (V) LED Current (mA) 19 19 0.55 0.50 17 0.45 VIN = 12V, fOSC = 1MHz VIN = 12V, fOSC = 1MHz 0.40 15 -50 -25 0 25 50 75 100 -50 125 -25 0 Temperature (°C) 25 50 75 100 125 Temperature (°C) LED Current vs. PWM Duty Cycle VISET vs. Input Voltage 90 0.70 80 LED Current (mA) 0.65 VISET (V) 0.60 0.55 0.50 70 60 50 PWM = 30kHz PWM = 10kHz PWM = 1kHz PWM = 120Hz 40 30 20 0.45 10 40 LEDs, fOSC = 1MHz VIN = 12V, fOSC = 1MHz 0 0.40 4 8 12 16 20 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8510A-01 January 2014 24 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8510A OVP Threshold vs. Input Voltage Switch Off Current vs. Temperature 1.5 Switch Off Current (mA) 1.5 OVP Threshold (V) 1.4 1.3 1.2 1.1 1.3 1.1 0.9 0.7 fOSC = 1MHz, VIN = 4.5V fOSC = 1MHz 1.0 0.5 4 8 12 16 20 24 -50 VIN (5V/Div) VIN (2V/Div) IOUT (50mA/Div) IOUT (50mA/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 25 50 75 100 125 Line Transient Response Line Transient Response Time (50ms/Div) 0 Temperature (°C) Input Voltage (V) VIN = 11V to 14V, fOSC = 1MHz -25 VIN = 4.5V to 5.5V, fOSC = 1MHz Time (50ms/Div) is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A Application Information The RT8510A is a general purpose 4-CH LED driver capable of delivering an adjustable 10 to 80mA LED current. The IC is a current mode Boost converter integrated with a 43V/2.5A power switch which can cover a wide VIN range from 4.2V to 24V. The switching frequency is adjustable by an external resistor from 500kHz to 2MHz. The part integrates built-in soft-start with PWM dimming control; moreover, it provides over-voltage, over-temperature and current limit protection features. Soft-Start The RT8510A equips a built-in soft-start feature to prevent high inrush current during start-up. The soft-start function prevents excessive input current and input voltage droop during power-on state. Compensation The control loop can be compensated by adjusting the external components connected to the COMP pin. The COMP pin is the output of the internal error amplifier. The compensation capacitors, C3 and C4, will adjust the integrator zero and pole respectively to maintain stability. Moreover, the resistor, R3, will adjust the frequency integrator gain for fast transient response. LED Connection The RT8510A equips 4-CH LED drivers with each channel supporting up to 12 LEDs. The LED strings are connected from the output of the Boost converter to pins 15, 16, 17 and 18, respectively. If one of the LED channels is not used, the LED pin should be opened directly. Over-Voltage Protection The RT8510A integrates Over-Voltage Protection (OVP) function. When the voltage at the OVP pin reaches the threshold voltage, the internal switch will be turned off. The internal switch will be turned on again once the voltage at the OVP pin drops below its threshold voltage. The OVP threshold voltage is adjustable and can be clamped at a certain voltage level and it can be calculated by the following equation : ⎛ R ⎞ VOUT(OVP) = VOVP × ⎜ 1 + OVP2 ⎟ ROVP1 ⎠ ⎝ ROVP1 and ROVP2 are resistors in the voltage divider connected to OVP pin. If at least one string is in normal operation, the controller will automatically ignore open strings and continue to regulate the current for the strings in normal operation. It is suggested to use 2MΩ for ROVP2 to reduce loading effect. Current Limit Protection The RT8510A can limit the peak current to achieve overcurrent protection. The RT8510A senses the inductor current during the “ON” period that flows through the LX pin. The duty cycle depends on the current signal and internal slope compensation in comparison with the error signal. The internal switch will be turned off when the current signal is larger than the internal slope compensation. In the “OFF” period, the inductor current will be decreased until the internal switch is turned on by the oscillator. Brightness Control Setting and Regulation of LED Current The LED current can be calculated by the following equation : ILED ≅ 95 RISET where RISET is the resistor between the ISET pin and GND. This setting is the reference for the LED current at channel 1-4 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to RISET. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8510A-01 January 2014 The RT8510A brightness dimming control is determined by the signal on the PWM pin with a suggested PWM frequency range from 120Hz to 30kHz. Referring to the following curve, the minimum dimming duty can be as low as 1% for the frequency range from 120Hz to 1kHz. For the dimming frequency from 1kHz to 10kHz, the dimming duty is at most 5%. If the frequency is increased to 30kHz, the dimming duty will be up to 10%. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8510A LED Current vs. PWM Duty Cycle IPEAK = 90 LED Current (mA) 80 where η is the efficiency of the power converter and T is the operating period. 70 60 50 Diode Selection PWM = 30kHz PWM = 10kHz PWM = 1kHz PWM = 120Hz 40 30 20 10 40 LEDs, fOSC = 1MHz 0 0 10 20 30 40 50 60 70 80 90 100 Duty Cycle (%) Figure 1 Over-Temperature Protection The RT8510A has an over-temperature protection function to prevent the IC from overheating due to excessive power dissipation. The OTP function will shut down the IC when junction temperature exceeds 160°C . Inductor Selection The value of the inductance L can be approximated by the following equation, where the transition is from discontinuous conduction mode (DCM) to continuous conduction mode (CCM) : L= VOUT × IOUT VIN × D × T + 2×L η × VIN D × (1 − D) × VOUT 2 × fOSC × IOUT 2 The duty cycle can be calculated according to the following equation : V − VIN D = OUT VOUT where VOUT is the maximum output voltage, VIN is the minimum input voltage, fOSC is the operating frequency and IOUT is the total current from all LED strings. The Boost converter operates in DCM over the entire input voltage range when the inductor value is below this value L. When inductance is greater than L, the converter operates in CCM at the minimum input voltage and may be discontinuous at higher voltages. The inductor must be selected with a saturated current rating that is greater than the peak current provided by the following equation : Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. The power dissipation, reverse voltage rating and pulsating peak current are important parameters for Schottky diode selection. Make sure that the diode's peak current rating exceeds IPEAK and reverse voltage rating exceeds the maximum output voltage. Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. If LED current is 20mA per channel, a 10μF ceramic capacitor is sufficient. A value higher or lower may be used depending on the noise level from the input supply and the input current to the converter. It is recommended to choose a ceramic capacitor based on the output voltage ripple requirements. The minimum value of the output capacitor COUT is given by the following equation : COUT = IOUT × D ΔVOUT × f where ΔVOUT is the peak to peak ripple voltage at the output. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = ( TJ(MAX) − TA ) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A For recommended operating condition specifications of the RT8510A, the maximum junction temperature is 125°C and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN28L 4x5 packages, the thermal resistance, θJA, is 28°C/ W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : P D(MAX) = (125°C − 25°C) / (28°C/W) = 3.57W for WQFN-28L 4x5 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 4.0 Four-Layer PCB 3.5 Layout Considerations PCB layout is very important for designing switching power converter circuits. The following layout guides should be strictly followed for best performance of the RT8510A. ` The power components, L1, D1, CIN, COUT must be placed as close to the IC as possible to reduce current loop. The PCB trace between power components must be as short and wide as possible. ` Place L1 and D1as close as possible to the LX pin . The trace should be as short and wide as possible. ` The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. Place the compensation components as close as possible to the COMP pin. ` The exposed pad of the chip should be connected to ground plane for thermal consideration. 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8510A-01 January 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8510A NC NC NC NC NC C2 NC Place C2 as close to the VIN pin as possible. 28 27 26 25 24 23 The compensation circuit should be kept away from power loops and shielded with a ground trace to prevent any noise coupling. GND R2 VIN 1 22 RT PWM 2 21 ISET EN 3 20 COMP LX 4 19 AGND R3 5 18 CH4 PGND 6 17 CH3 PGND 7 16 CH2 OVP 8 15 CH1 9 10 11 12 13 14 NC NC 29 NC Place the power components as close to the IC as possible. The traces should be wide and short, especially for the high-current loop. LX NC VOUT GND NC L1 D1 C3 C4 NC + CIN COUT GND VIN Figure 3. PCB Layout Guide Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS8510A-01 January 2014 RT8510A Outline Dimension 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 3.900 4.100 0.154 0.161 D2 2.600 2.700 0.102 0.106 E 4.900 5.100 0.193 0.201 E2 3.600 3.700 0.142 0.146 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 28L QFN 4x5 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS8510A-01 January 2014 www.richtek.com 13