RT8567 6-CH 43V WLED Driver General Description Features The RT8567 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 current mode boost z The RT8567 has a wide input voltage range from 2.7V to 24V and can provide adjustable LED current from 5mA to 40mA. The internal 250m, 43V power switch with current mode control provides cycle-by-cycle over current protection. The RT8567 also integrates PWM dimming function for accurate LED current control. The input PWM dimming frequency can operate from 200Hz to 25kHz without inducing any inrush in LED current or inductor current. The switching frequency of the RT8567 is also adjustable from 500kHz to 2MHz, which allows flexibility between efficiency and component size. High Output Voltage : Up to 43V z Channel Current Programmable : 5mA to 40mA z Channel Current Regulation with Accuracy 3% and Matching 2% z Dimming Controls : External PWM Input Up to 25kHz z Adjustable Switching Frequency : 500kHz to 2MHz z Built-In Soft-Start z Protections LED Strings Open Detection Current Limit Protection Programmable Over Voltage Protection Over Temperature Protection z 20-Lead WQFN Package z RoHS Compliant and Halogen Free z Applications z z UMPC and Notebook Computer Backlight GPS, Portable DVD Backlight Pin Configurations (TOP VIEW) PWM VIN COMP NC LX controller drives six strings in parallel and supports up to 12 WLEDs per string. The internal current sinks support a maximum of 2% current mismatching for excellent brightness uniformity in each string of LEDs. To provide enough headroom for current sink operation, the boost controller monitors the minimum voltage of the feedback pins and regulates an optimized output voltage for power efficiency. Wide Input Voltage : 2.7V to 24V The RT8567 is available in a thin WQFN-20L 3x3 package. 20 19 18 17 16 Ordering Information VDC EN RT ISET NC RT8567 Package Type QW : WQFN-20L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) RoHS compliant and compatible with the current require- 3 AGND 13 4 21 12 5 11 8 9 10 CH6 CH5 CH4 AGND CH3 7 PGND OVP NC CH1 CH2 Marking Information JY= : Product Code Suitable for use in SnPb or Pb-free soldering processes. JY=YM DNN DS8567-00 April 2011 14 WQFN-20L 3x3 Richtek products are : ments of IPC/JEDEC J-STD-020. 15 2 6 Note : 1 YMDNN : Date Code www.richtek.com 1 RT8567 Typical Application Circuit 10H L1 VIN 3V to 8.5V CIN 10F C2 1F D1 R2 10 19 Chip Enable 2 20 PWM Signal 3 RRT 51k 1 16 LX ROVP2 VIN OVP 14 RT8567 EN PWM CH1 12 RT CH2 11 CH3 VDC : : : : : : : : : : : : : 6 LEDs by : : String 10 CH5 7 CH6 6 4 ISET C3 10nF : : : CH4 8 18 COMP C4 Open OVP setting <24V ROVP1 CDC 0.1F R3 10k VOUT 19.6V(MAX) COUT 10F AGND 9, 21 (Exposed Pad) PGND 15 RISET 51k Figure 1. Application Circuit 1 10H L1 VIN 6V to 24V CIN 10F C2 1F D1 R2 10 19 Chip Enable 2 20 PWM Signal 3 RRT 51k 1 16 LX OVP 14 RT8567 PWM CH1 12 RT CH2 11 CH3 C3 10nF 4 ISET RISET 51k : : : : : : : : : : : : : : : : 12 LEDs by : : String 10 CH4 8 18 COMP C4 Open ROVP1 EN CDC 0.1F R3 10k ROVP2 VIN VDC VOUT 43V(MAX) COUT 10F CH5 7 CH6 6 AGND 9, 21 (Exposed Pad) PGND 15 Figure 2. Application Circuit 2 www.richtek.com 2 DS8567-00 April 2011 RT8567 10H L1 VIN 3V to 8.5V CIN 10F D1 16 LX 19 5V C2 1F ROVP2 OVP 14 VIN RT8567 2 VOUT 19.6V(MAX) COUT 10F ROVP1 : : : : : : : : : : : : : : : : 6 LEDs by : : String EN CH1 12 20 PWM Signal 3 1 RRT 51k PWM RT VDC CDC 0.1F R3 10k C3 10nF 4 ISET RISET 51k CH3 10 CH4 8 CH5 7 18 COMP C4 Open CH2 11 CH6 6 AGND 9, 21 (Exposed Pad) PGND 15 Figure 3. Application Circuit 3 Functional Pin Description Pin No. Pin Name Pin Function 1 VDC Internal Regulator Voltage. Connect a capacitor to ground. 2 EN Chip Enable Pin (Active High). Note that this pin is high impedance. There should be a pull low 100k resistor connected to AGND when the control signal is floating. 3 RT 4 ISET 5, 13, 17 6, 7, 8, Frequency Set Input. Used to set the switching frequency of the boost converter. Connect a resistor to ground. LED Current Set Pin. LED Current is Set by the Value of the Resistor RISET Connected from the ISET Pin to ground. Do not short the ISET pin to ground. VISET is typical 1V. NC No Internal Connection. CH6 to CH4 Current Sink Regulation Input. This pin should be connected to the cathode of LEDs if used. Otherwise, it should be connected to ground. 9, 21 (Exposed Pad) AGND Analog Ground of LED Driver. The exposed pad must be soldered to a large PCB and connected to AGND for maximum power dissipation. CH3 to CH1 Current Sink Regulation Input. This pin should be connected to the cathode of LEDs if used. Otherwise, it should be connected to ground. 14 OVP Over Voltage Protection for Boost Converter. The detecting threshold is 1.2V. 15 PGND Power Ground of Boost Converter. 16 LX Switching Node for Boost Converter. 18 COMP Compensation Pin for Error Amplifier. Connect a compensation network to ground. 19 VIN LED Power Supply Input. 20 PWM PWM Dimming Control Input. 10,11,12 DS8567-00 April 2011 www.richtek.com 3 RT8567 Function Block Diagram VIN VDC RT OVP + 1.2V - EN Enable Control OSC S Q R Q LX OCP & OTP PWM Controller + + PGND + EA - COMP VDS Mini LED Selection 6 PWM LED Open Detection ...... CH1 CH2 CH6 + - 1V + + - - ...... + - ISET AGND www.richtek.com 4 DS8567-00 April 2011 RT8567 Absolute Maximum Ratings z z z z z z z z z z (Note 1) VIN to GND -----------------------------------------------------------------------------------------------------------------EN, PWM, VDC, ISET, COMP, RT to GND -------------------------------------------------------------------------LX to GND ------------------------------------------------------------------------------------------------------------------OVP, (CH1 to CH6) to GND --------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25C -0.3V to 26.5V -0.3V to 26.5V -0.3V to 48V -0.3V to 48V WQFN-20L 3x3 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-20L 3x3, JA -----------------------------------------------------------------------------------------------------WQFN-20L 3x3, JC -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM -------------------------------------------------------------------------------------------------------------------------MM ---------------------------------------------------------------------------------------------------------------------------- 1.471W Recommended Operating Conditions z z z 68C/W 7.5C/W 260C 150C -65C to 150C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 2.7V to 24V Junction Temperature Range -------------------------------------------------------------------------------------------- -40C to 125C Ambient Temperature Range -------------------------------------------------------------------------------------------- -40C to 85C Electrical Characteristics (VIN = 4.5V, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit I VCC VCOMP = 0V, No Switching -- 2 -- I VCC_LX VCOMP = 2V, Switching -- 3 -- Shutdown Current I SHDN VIN Under Voltage Lockout Threshold VUVLO VIN = 4.5V, EN = 0 VIN Rising VIN Falling ---- -2.3 2.1 20 --- VIN = 2.7V to 24V 2 -- -- VIN = 2.7V to 24V VIN = 2.7V to 24V VIN = 2.7V to 24V -1.5 -- ---- 0.8 -0.6 -0.9 -- 2 1 0.5 -1.1 -- MHz VIN Quiescent Current mA A V Control Input EN Input Voltage Threshold PWM Input Voltage Threshold Logic-High VIH Logic-Low VIL Logic-High VIH Logic-Low VIL V V Boost Converter Switching Frequency fOSC RRT = 25k RRT = 51k RRT = 100k LX On Resistance (N-MOSFET) RDS(ON) VIN > 4.5V -- 0.25 -- Minimum On Time tMON f OSC = 1MHz -- 120 -- ns Maximum Duty DMAX VCOMP = 2V, Switching -- 94 -- % LX Current Limit ILIM 1.6 2 2.4 A Regulated VCHx VCHx -- 0.6 DS8567-00 April 2011 Highest LED String, ILED = 20mA -V To be continued www.richtek.com 5 RT8567 Parameter Symbol Test Conditions Min Typ Max Unit 2V > VCHx > 0.6V, RISET = 51k 2V > VCHx > 0.6V, RISET = 51k, Calculating (ILEDx - IAVG ) x 100% I AVG -3 -- 3 % -- 0.5 2 % LED Current Programming LED Current Accuracy I LEDA LED Current Matching I LEDM ISET Pin Voltage Fault Protection Over Voltage Threshold VISET -- 1 -- V VOVP -- 1.2 -- V OVP Fault VOVP_FAULT -- 50 -- mV TSD -- 150 -- C -- 60 -- mV Thermal Shutdown Temperature LED Channel Under Voltage Threshold VLSD No-Connection Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. JA is measured in the natural convection at TA = 25C on a high effective thermal conductivity four-layer test board of JEDEC 51-7 thermal measurement standard. The measurement case position of JC is on 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. www.richtek.com 6 DS8567-00 April 2011 RT8567 Typical Operating Characteristics Efficiency vs. Input Voltage LED Current vs. Input Voltage 100 26 Output Current (mA) 80 Efficiency (%) LED1 LED2 LED3 LED4 LED5 LED6 24 60 40 20 22 20 18 16 60LEDs, PWM = 3.3V, fOSC = 1MHz 10LEDs per channel, PWM = 3.3V, fOSC = 1MHz 0 14 4 8 12 16 20 24 4 8 12 Input Voltage (V) 20 24 Input Voltage (V) LED Current vs. Temperature ISET Voltage vs. Temperature 1.20 26 1.15 ISET Voltage (V) 24 LED Current (mA) 16 22 20 18 16 1.10 1.05 1.00 0.95 0.90 0.85 10LEDs per channel, PWM = 3.3V, fOSC = 1MHz 10LEDs per channel, fOSC = 1MHz 14 0.80 -50 -25 0 25 50 75 100 -50 125 -25 0 25 50 75 100 125 Temperature (C) Temperature (C) ISET Voltage vs. Input Voltage LED Current vs. PWM Duty Cycle 1.20 20 1.15 LED Current (mA) ISET Voltage (V) 16 1.10 1.05 1.00 0.95 0.90 12 PWM = 200Hz PWM = 1kHz PWM = 10kHZ PWM = 25kHz 8 4 0.85 10LEDs per channel, fOSC = 1MHz 0.80 10LEDs per channel, fOSC = 1MHz 0 4 8 12 16 Input Voltage (V) DS8567-00 April 2011 20 24 0 20 40 60 80 100 PWM Duty Cycle (%) www.richtek.com 7 RT8567 Quiescent Current vs. Temperature OVP Threshold Voltage vs. Input Voltage 3.00 Quiescent Current (mA) 1 OVP Threshold Voltage (V) 1.5 1.4 1.3 1.2 1.1 2.75 2.50 2.25 2.00 1.75 1.50 1.25 VIN = 12V, fOSC = 1MHz 10LEDs per channel, fOSC = 1MHz 1.00 1.0 4 8 12 16 20 24 -50 0 25 50 75 100 Input Voltage (V) Temperature (C) Line Transient Response Line Transient Response VIN (5V/Div) VIN (2V/Div) I LED (50mA/Div) I LED (50mA/Div) VIN = 11V to 14V, PWM = 3.3V, fOSC = 1MHz Time (50ms/Div) Time (50ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VOUT (20V/Div) VOUT (20V/Div) I LED (20mA/Div) I LED (20mA/Div) VIN = 12V, PWM = 3.3V, fOSC = 1MHz Time (5ms/Div) 125 VIN = 4.5V to 5.5V, PWM = 3.3V, fOSC = 1MHz VEN (5V/Div) www.richtek.com 8 -25 VIN = 12V, PWM = 3.3V, fOSC = 1MHz Time (25ms/Div) DS8567-00 April 2011 RT8567 Application Information Input UVLO The input operating voltage range of the RT8567 is from 2.7V to 24V. An input capacitor at the VIN pin can reduce ripple voltage. It is recommended to use a ceramic 10F or larger capacitance as the input capacitor. This IC provides an Under Voltage Lockout (UVLO) function to enhance the stability during startup. The UVLO threshold of the input rising voltage is set at 2.3V typically with a 0.2V hysteresis. Soft-Start The function of the soft-start is defined by two periods. The first period is capped at the peak current limit with the time decided by the ratio of VOUT and VIN. However, an external capacitor, VOUT, can also affect the time of charging. The second period is defined by the slowly ramping of the ILED current by the ISET voltage. Thus, the inrush current is limited by the boost converter and current regulator. 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. Setting and Regulation of LED current The LED current can be calculated by the following equation : 1020 ILED = RISET where, RISET is the resistor between the ISET pin and GND. This setting is the reference for the LED current at CH1 to CH6 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Brightness Control The RT8567 brightness dimming is determined by the signal on the PWM pin with a suggested PWM frequency range from 200Hz to 25kHz. Referring to the following curve, the minimum dimming duty can be as low as 1% for the frequency range from 200Hz to 1kHz. For the frequency range from 1kHz to 10kHz, the dimming duty is at most 5%. If the frequency is increased to 25kHz, the dimming duty will be up to 10%. LED Current vs. PWM Duty Cycle 20 16 LED Current (mA) The RT8567 is a current mode boost converter capable of powering to 72 white LEDs with a programmable current for uniform intensity. The part integrates current sources, soft-start, and easy analog and digital dimming control. The protection block provides the circuitry for over temperature, over voltage and current limit protection features. 12 PWM = 200Hz PWM = 1kHz PWM = 10kHZ PWM = 25kHz 8 4 0 0 20 40 60 80 100 PWM Duty Cycle (%) Figure 1 LED Connection Over Voltage Protection The RT8567 equips 6-CH LED drivers with each channel supporting up to 12 LEDs. The 6 LED strings are connected from VOUT to pin 6, 7, 8, 10, 11, and 12 respectively. If one of the LED channels is not used, the unused LED pin should be opened directly. The RT8567 equips an Over Voltage Protection (OVP) function. When the voltage at the OVP pin reaches a threshold of approximately 1.2V, the MOSFET driver turns off. The MOSFET driver turns on again once the voltage at OVP drops below the threshold voltage. Thus, the DS8567-00 April 2011 www.richtek.com 9 RT8567 output voltage can be clamped at a certain voltage level. This voltage level can be calculated by the following equation : 1+ROVP2 VOUT, OVP = VOVP x ( ) ROVP1 the entire input voltage range when the L1 inductor value is less than this value L. With an inductance greater than L, the converter operates in continuous mode at the minimum input voltage and may be discontinuous at higher voltages. where ROVP1 and ROVP2 are the resistors in the voltage divider connected to the OVP pin. If at least one string is in normal operation, the controller will automatically ignore the open strings and continue to regulate the current for the string(s) in normal operation. The selected inductor must be selected with saturation current rating greater than the peak current provided by the following equation : V xI V - VIN V xT IPEAK = ( OUT OUT ) + ( IN ) x ( OUT ) x VIN 2xL VOUT Current Limit Protection Diode Selection The RT8567 can limit the peak current to achieve over current protection. The RT8567 senses the inductor current through LX pin in the ON period. The duty cycle depends on the current sense signal summed with the internal slope compensation and compared to the COMP signal. The internal N-MOSFET will be turned off when the current signal is larger than the COMP signal. In the OFF period, the inductor current will descend. The internal MOSFET is turned on by the oscillator in the next starting cycle. Schottky diode is a good choice for any asynchronous boost converter due to its small forward voltage and fast switching Speed. However, when selecting a Schottky diode, important parameters such as power dissipation, reverse voltage rating and pulsating peak current must all be taken into consideration. Choose a suitable diode with reverse voltage rating greater than the maximum output voltage. Over Temperature Protection The RT8567 has an over temperature protection (OTP) function to prevent excessive power dissipation from overheating the device. The OTP will shut down switching operation when the junction temperature exceeds 150C. Inductor Selection The value of the output inductor (L), where the transition from discontinuous to continuous mode occurs is approximated by the following equation : L= Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most applications, a 10F 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, can be calulated by the following equation : COUT = (VOUT - VIN ) x IOUT x VRIPPLE x VOUT x f (VOUT - VIN ) x VIN2 2 x IOUT x f x VOUT 2 where, VOUT = maximum output voltage. VIN = minimum input voltage. f = operating frequency. IOUT = sum of current from all LED strings. is the efficiency of the power converter. The boost converter operates in discontinuous mode over www.richtek.com 10 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) / JA DS8567-00 April 2011 RT8567 where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and JA is the junction to ambient thermal resistance. For recommended operating condition specifications of the RT8567, the maximum junction temperature is 125C and TA is the ambient temperature. The junction to ambient thermal resistance, JA , is layout dependent. For WQFN-20L 3x3 packages, the thermal resistance, JA, is 68C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25C can be calculated by the following formula : PD(MAX) = (125C - 25C) / (68C/W) = 1.471W for WQFN-20L 3x3 package PCB layout is very important for designing switching power converter circuits. The following layout guides should be strictly followed for best performance of the RT8567. 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 D1 as close to the LX pin as possible. The trace should be as short and wide as possible. The compensation circuit should be kept away from the power loops and shielded with a ground trace to prevent any noise coupling. Place the compensation components as close to the COMP pin as possible. The exposed pad of the chip should be connected to ground plane for thermal consideration. The compensation circuit should be kept away from The power loops and shielded with a ground trace to prevent any noise coupling. Four-Layer PCB CIN 1.4 C2 1.2 1.0 0.4 RISET 0.2 GND 0.0 0 25 50 75 100 Ambient Temperature (C) Figure 2. Derating Curve for RT8567 Package DS8567-00 April 2011 125 C4 L1 D1 VOUT PWM VIN COMP NC LX Locate RISET as close to ISET as possible. 0.6 GND C3 R3 Locate the C2 as close to VIN as possible. 0.8 Place the power components as Close as possible. The traces should be wide and short especially for the high current loop. VIN GND 1.6 COUT 20 19 18 17 16 VDC EN RT ISET NC 1 15 2 14 3 AGND 4 21 5 13 12 11 6 7 8 PGND OVP NC CH1 CH2 9 10 CH6 CH5 CH4 AGND CH3 Maximum Power Dissipation (W)1 The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, JA. For the RT8567 package, the derating curve in Figure 2 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Layout Considerations Figure 3. PCB Layout Guide www.richtek.com 11 RT8567 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. Dimensions In Millimeters Dimensions In Inches Symbol 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 0.150 0.250 0.006 0.010 D 2.900 3.100 0.114 0.122 D2 1.650 1.750 0.065 0.069 E 2.900 3.100 0.114 0.122 E2 1.650 1.750 0.065 0.069 e L 0.400 0.350 0.016 0.450 0.014 0.018 W-Type 20L QFN 3x3 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: marketing@richtek.com Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. www.richtek.com 12 DS8567-00 April 2011