® RT8566 High Voltage 8-CH LED Driver General Description Features The RT8566 is an 8-CH LED driver capable of delivering 120mA for each channel. The RT8566 is a current mode boost converter with an adjustable switching frequency via the RT pin from 100kHz to 1MHz and a wide VIN range from 9V to 28V. Wide Input Supply Voltage Range : 9V to 28V Adjustable Boost Controller Switching Frequency from 100kHz to 1MHz Programmable Channel Current Channel Current Matching : ±1.5% External Dimming Control Boost MOSFET Over Current Protection Automatic LED Open/Short Protection to Avoid Output Over Voltage VCC Under Voltage Lockout Adjustable Over Voltage Protection Under Voltage Protection Thermal Shutdown Protection Abnormal Status Indicator for Open/Short/Thermal Condition RoHS Compliant and Halogen Free The PWM output voltage loop selects and regulates the LED pin with the highest voltage string to 0.6V, hence allowing voltage mismatches between LED strings. The RT8566 automatically detects and disconnects any unconnected and/or broken strings during operation from PWM loop to prevent VOUT from over voltage. The 1.5% matched LED currents on all channels are simply programmed with a resistor. A very high contrast ratio true digital PWM dimming can be achieved by driving the PWM pin with a PWM signal. When an abnormal situation (open/short/thermal) occurs, a status signal will be sent to the system to shut down the IC. Applications The RT8566 is available in a TSSOP-28 (Exposed Pad) package. Ordering Information RT8566 Package Type CP : TSSOP-28 (Exposed Pad-Option 1) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Marking Information LCD TV, Monitor Display Backlight LED Driver Application General Purpose Constant Current Source Pin Configurations (TOP VIEW) OVP/UVP RISET NC PWM NC STATUS NC RT VC SS EN SEN PGND DRV 28 2 27 3 26 4 25 5 24 6 23 7 8 GND 22 21 9 20 10 19 11 18 12 13 14 17 29 16 15 GND GND GND GND LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8 VCC CREG TSSOP-28 (Exposed Pad) RT8566GCP : Product Number RT8566 GCPYMDNN YMDNN : Date Code Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8566 Typical Application Circuit L1 10µH VIN 9 to 28V D1 CIN 47µF CVCC 1µF RSENSE 100m RF2 0 RT8566 LED1 12 SEN LED8 CF 1nF PWM Signal 24 17 RSTATUS 100k 14 DRV 1k RISET 4 PWM RT Chip Enable : : : …… : : : : : STATUS 6 RDRV 5 1k 11 EN RC 560 COUT 4.7µF x 6 …… RF1 100 ROVP1 82k …… MSW ROVP2 3.6M OVP/UVP 1 16 VCC VOUT 45V 9 CC 0.22µF 2 RISET 4.53k 8 RRT 56k SS 10 CREG VC PGND 13 15 VIN FLT CSS 0.1µF CREG 1µF GND 25, 26, 27, 28, 29 (Exposed Pad) Figure 1. General Application FLT VIN 9 to 28V L1 10µH D1 CIN 47µF CVCC 1µF RSENSE 100m RF2 0 RT8566 LED1 12 SEN CF 1nF Chip Enable : : : …… : : : : : 24 17 RSTATUS 100k STATUS 6 RDRV 5 PWM Signal LED8 14 DRV 1k 4 PWM 1k 11 EN RC 560 CC 0.22µF 9 VC PGND 13 RISET RT RISET 4.53k 8 RRT 56k 15 VIN FLT 2 SS 10 CREG COUT 4.7µF x 6 …… RF1 100 ROVP1 82k …… MSW OVP/UVP 1 16 VCC VOUT 45V ROVP2 3.6M CSS 0.1µF CREG 1µF GND 25, 26, 27, 28, 29 (Exposed Pad) Figure 2. External P-MOSFET Isolation Application Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8566-03 November 2013 RT8566 Functional Pin Description Pin No. Pin Name Pin Function NC Over Voltage and Under Voltage Protection. PWM boost converter turns off when VOVP or VUVP goes higher than 1.2V or lower than 0.6V, respectively. LED Current Set Pin. A resistor or a current from DAC on this pin programs the full LED current. No Internal Connection. 4 PWM Dimming Control Input. 6 STATUS Boost Converter Operation Status Output. 8 RT Switching Frequency Set. Connect a resistor between RT and GND to set the boost converter switching frequency. 9 VC 10 SS 11 EN 12 SEN 13 PGND 14 DRV 15 CREG 16 VCC 1 OVP/UVP 2 RISET 3, 5, 7 17 to 24 LED8 to LED1 25, 26, 27, 28 GND 29 (Exposed pad) PWM Boost Converter Loop Compensation Node. Soft-Start Pin. Place a capacitor of at least 10nF from this pin to GND to set the soft-start time period. Chip Enable. When EN is pulled low, chip will be in shutdown mode. Current Sense Input. During normal operation, this pin senses the voltage across the external inductor current sensing resistor for peak current mode control and also to limit the inductor current during every switching cycle. Boost Converter Power Ground. Boost Converter Power Switch Gate Output. This pin drives the external power N-MOSFET device. 1F capacitor should be placed on this pin to stabilize the 5V output of the internal regulator. This regulator is for chip internal use only. Power Supply of the Chip. For good bypass, a low ESR capacitor close to the pin is required. Channel 8 to Channel 1 LED Current Sink. Leave the pins unconnected if not used. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8566 Function Block Diagram DRV SEN OSC RT VCC STATUS OVP - UVLO UVP OTP S + R OVP/UVP + - 0.6V + R LED Short LED1 UVP + - EN - 5V LDO VC Shutdown + CREG + - 1.2V ………………… 1.2V LED8 VOUT Regulation Unit + 5V - 6µA SS PWM GND PGND + - RISET Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8566-03 November 2013 RT8566 Absolute Maximum Ratings (Note 1) Supply Voltage, VCC , STATUS ----------------------------------------------------------------------------------------LED1 to LED8 --------------------------------------------------------------------------------------------------------------PWM, EN, DRV, SEN, SS, VC, RT, CREG, OVP/UVP, RISET ------------------------------------------------Power Dissipation, PD @ TA = 25°C TSSOP-28 (Exposed Pad) ----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSSOP-28 (Exposed Pad), θJA -----------------------------------------------------------------------------------------TSSOP-28 (Exposed Pad), θJC ----------------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions 33V 50V 5.5V 3.571W 28°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Voltage, VCC ------------------------------------------------------------------------------------------------------LED1 to LED8 --------------------------------------------------------------------------------------------------------------Junction Temperature Range --------------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------------- 9V to 28V 45V −40°C to 125°C −40°C to 85°C Electrical Characteristics (VCC = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Voltage Supply Current IVCC Switching Off -- 5 -- mA Shutdown Current ISHDN VEN 0.7V -- -- 10 A VDD LDO Output VCREG -- 5 -- V VDD LDO Capability ICREG 30 -- -- mA VCC UVLO Threshold VUVLO EN Input Threshold Voltage VCC Rising -- -- 8 Hysteresis -- 1.4 -- V Logic-High VENH 1.5 -- -- V Logic-Low VENL -- -- 0.8 V 114 120 126 mA -- 1.5 3 % -- 0.6 -- V LED Current Programming LED Current Accuracy LED Current Matching RISET = 4.53k, V PWM 1.2V RISET = 4.53k, V PWM 1.2V I(MAX) I(MIN) 2 I(Avg) LED1 to LED8 Regulation Voltage Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 100% ILED = 120mA is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 ® RT8566 Parameter Symbol VLED Threshold Test Conditions No Connection RISET Pin Voltage Dimming PWM Input Threshold Voltage Min Typ Max Unit -- 0.1 -- V -- 1.2 -- V Logic-High VPW MH 1.2 -- -- Logic-Low VPW ML -- -- 0.4 RRT = 24k -- 1 -- MHz RRT = Open -- 100 -- kHz V PWM Boost Controller Switching Frequency fSW Minimum On Time tON -- 100 -- ns Maximum Duty Cycle Dmax 80 -- -- % -- 0.5 -- V Gate Driver Source -- 2.5 -- A Gate Driver Sink -- 3 -- A SEN Current Sense Limit Input Current Limit OVP, UVP, SCP, OTP and Soft-Start OVP Threshold VOVP 1.1 1.2 1.3 V UVP Threshold VUVP 0.57 0.6 0.63 V SCP Threshold VSCP LED1 to LED8 -- 4.3 -- V Soft-Start Current ISS VSS 2.5V -- 6 -- A Thermal Shutdown Temperature TSD Lockout Temperature Point -- 150 -- C Thermal Shutdown Hysteresis TSD Resume Temperature Point -- 20 -- C STATUS Low Voltage VSTATUS Open Drain at 10mA -- -- 0.5 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. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 6 ® RT8566 Typical Operating Characteristics LED Current vs. Input Voltage LED Current vs. PWM Duty Cycle 120 100 140 LED Current (mA) LED Current (mA) 160 120 LED1 LED2 LED3 LED4 LED5 LED6 LED7 LED8 100 80 80 PWM = 200Hz PWM = 1kHz PWM = 10kHz 60 40 20 96LEDs, RISET = 4.3kΩ VIN = 12V, 96LEDs, RISET = 4.3kΩ 0 60 8 10 12 14 16 18 20 22 24 26 0 28 10 20 30 40 50 60 70 Input Voltage (V) PWM Duty Cycle (%) Efficiency vs. Input Voltage Power On from VIN 80 90 100 100 Efficiency (%) 95 90 VIN (5V/Div) 85 DRV (5V/Div) 80 75 96LEDs, RISET = 4.3kΩ 70 8 10 12 14 16 18 20 22 24 26 I IN (1A/Div) VIN = 12V, CSS = 0.1μF, 96LEDs, RISET = 9.1kΩ Time (5ms/Div) 28 Input Voltage (V) Power On from EN Power On from PWM VEN (2V/Div) PWM (2V/Div) DRV (5V/Div) DRV (5V/Div) I IN (1A/Div) VIN = 12V, CSS = 0.1μF, 96LEDs, RISET = 9.1kΩ Time (5ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 I IN (1A/Div) VIN = 12V, CSS = 0.1μF, 96LEDs, RISET = 9.1kΩ Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8566 Application information The RT8566 is an 8-CH driver controller that delivers well matched LED current to each channel of LED strings. The external N-MOSFET current source will accommodate the power dissipation difference among channels resulting from the forward voltage difference between the LED strings. With high speed current source N-MOSFET drivers, the RT8566 features highly accurate current matching, while also providing very fast turn-on and turn-off times. This allows a very narrow minimum on or off pulse. The RT8566 integrates adjustable switching frequency and soft-start and provides circuitry for over temperature, over voltage, under voltage and current limit protection. Soft-Start The RT8566 employs a soft-start feature to limit the inrush current. The soft-start circuit prevents excessive inrush current and input voltage droop. The soft-start time is determined by a capacitor, CSS, connected between SS and GND and charged with a 6μA constant current as shown in the following equation. tSS (max) = CSS x 4.8 x 105 (s) The value of capacitor CSS is user-defined to satisfy the designer' requirement. Compensation Setting and Regulation of LED current The LED current can be calculated by the following equation : 543.6 ILED RISET where RISET is the resistor between the RISET pin and GND. This setting is the reference for the LED current at pin LEDx and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Over Voltage and Under Voltage Protection The RT8566 integrates Over Voltage Protection (OVP) and Under Voltage Protection (UVP). When the voltage at the OVP/UVP pin rises above the threshold voltage of approximately 1.2V or falls below the threshold voltage of approximately 0.6V, the internal switch will be turned off and STATUS pin will be pulled high. The internal switch will be turned on again once the voltage at the OVP/UVP pin returns to normal range. The output voltage can be clamped at a certain voltage level and can be calculated by the following equations : R VOUT(OVP) = VOVP x 1 + OVP2 R OVP1 R VOUT(UVP) = VUVP x 1 + OVP2 R OVP1 The regulator loop can be compensated by adjusting the external components connected to the VC pin. The VC pin is the output of the internal error amplifier. The compensation capacitor will adjust the integrator zero to maintain stability and the resistor value will adjust the frequency integrator gain for fast transient response. Typical values of the compensation components are RC = 560Ω, CC = 0.22μF. where ROVP1 and ROVP2 are the resistors in the resistive voltage divider connected to the OVP/UVP 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 strings in normal operation. Suggested value for ROVP2 is up to 3MΩ to prevent loading effect. LED Connection LED Short Circuit Protection The RT8566 equips 8-CH LED drivers and each channel supports up to 15 LEDs. The LED strings are connected from the output of the boost converter to pin LEDx (x = 1 to 8) respectively. If one of the LED channel is not in use, the LED pin should be opened directly. The RT8566 integrates LED Short Circuit Protection (SCP). If one of the LED1 to LED8 pin voltages exceeds a threshold of approximately 4.3V during normal operation, the STATUS pin will be pulled high for a fault signal. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8566-03 November 2013 RT8566 STATUS Over Temperature Protection After the IC is enable. STATUS will output logic high if LED Short/OVP/UVP/OTP conditions exist. STATUS will be reset after VIN or EN is re-applied. The RT8566 has over temperature protection function to prevent the IC from overheating due to excessive power dissipation. The IC will shut down and the STATUS pin will be pulled high when junction temperature exceeds 150°C. Main converter starts switching after junction temperature cools down by approximately 20°C. Setting the Switching Frequency The RT8566 switching frequency is programmable from 100kHz to 1MHz by adjusting the oscillator resistor, RRT. The switching frequency can be calculated by the following equation : 21.6 x 109 fSW 100k + RRT Current Limit Protection Brightness Control The RT8566 features a digital dimming control scheme. A very high contrast ratio true digital PWM dimming is achieved by driving the PWM pin with a PWM signal. The recommended PWM frequency is 200Hz to 10kHz, but the LED current cannot be 100% proportional to duty cycle, especially for high frequency and low duty ratio. Table 1. Dimming Frequency (Hz) Duty (Min.) Duty (Max.) 200 < f PWM 500 0.2% 100% 500 < fPWM 1k 0.4% 100% 1k < fPWM 2k 0.7% 100% 2k < fPWM 5k 1.4% 100% 5k < fPWM 10k 3.3% 100% Note : The minimum duty in Table 1 is based on the application circuit and does not consider the deviation of current linearity. Copyright © 2013 Richtek Technology Corporation. All rights reserved. November 2013 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) : 2 The RT8566 can sense the RSENSE voltage between the SEN pin and GND to achieve over current protection. The boost converter senses the inductor current during the on period. The duty cycle depends on the current signal and internal slope compensation compared with the error signal. The external switch will be turned off when the current signal is larger than the internal slope compensation. In the off period, the inductor current will decrease until the internal switch is turned on by the oscillator. The current limit value can be calculated by the following equation : 0.5V Current Limit (A) RSENSE DS8566-03 Inductor Selection L= D x 1 D x VOUT 2 x f x IOUT The duty cycle can be calculated as the following equation : D= VOUT VIN VOUT where VOUT is the maximum output voltage, VIN is the minimum input voltage, f is the operating frequency, and IOUT is the sum of current from all LED strings. The boost converter operates in DCM over the entire input voltage range when the inductor value is less than this value, L. With an inductance 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 as provided by the following equation : IPEAK = VOUT x IIOUT VIN x D x T η x VIN 2xL where η is the efficiency of the power converter. Diode Selection Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. Power dissipation, reverse voltage rating, and pulsating peak current are important parameters for consideration when making a Schottky diode selection. Make sure that the diode's peak current rating exceeds IPEAK and reverse voltage rating exceeds the maximum output voltage. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8566 The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For general applications, six 4.7μF ceramic capacitors are 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. The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. For the RT8566 packages, the derating curve in Figure 3 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Maximum Power Dissipation (W) Capacitor Selection 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 calculated by the following equation : COUT = IOUT x D VOUT x f where ΔVOUT is the peak-to-peak ripple voltage at the output. PD(MAX) = (TJ (MAX) − TA) / θJA where TJ (MAX) is the maximum junction temperature, TA is the ambient temperature, and θJAis the junction to ambient thermal resistance. For recommended operating condition specifications of the RT8566, the maximum junction temperature is 125°C and TA is the ambient temperature. The junction to ambient thermal resistance, θJA, is layout dependent. For TSSOP28 (Exposed Pad) 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 : 3.2 2.8 2.4 2.0 1.6 1.2 0.8 0.4 0.0 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 : Four-Layer PCB 3.6 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curve for RT8566 Packages Layout Considerations Careful PCB layout is very important for designing switching power converter circuits. The following layout guidelines should be strictly followed for best performance of the RT8566. The power components L1, D1, CIN, COUT must be placed as close as possible to the IC to reduce current loop. The PCB trace between power components must 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, RC and CC, as close as possible to pin 9. The exposed pad of the chip should be connected to ground plane for thermal consideration. PD(MAX) = (125°C − 25°C / (28°C/W) = 3.571W for TSSOP-28 (Exposed Pad) package Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8566-03 November 2013 RT8566 OVP/UVP The compensation RISET circuit should be kept NC away from the power PWM loops and shielded NC with a ground trace to prevent any noise STATUS NC coupling. RT VC SS GND CC RC EN SEN PGND VOUT DRV D1 27 3 26 4 25 5 24 6 23 7 8 22 GND 21 9 20 10 19 11 18 17 12 29 13 16 15 14 L1 COUT RDRV VIN CIN VIN RF1 CF GND + MSW RF2 GND GND GND GND LED1 LED2 LED3 LED4 LED5 LED6 LED7 Locate CVCC as close LED8 to VCC as possible. VCC CREG CVCC 28 2 RSENSE PGND Place the power components as close as possible to the IC. The traces should be wide and short especially for the high-current loop. Figure 4. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8566-03 November 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8566 Outline Dimension Dimensions In Millimeters Sym bol Dimensions In Inches Min Max Min Max A 1.000 1.200 0.039 0.047 A1 0.000 0.150 0.000 0.006 A2 0.800 1.050 0.031 0.041 b 0.190 0.300 0.007 0.012 D 9.600 9.800 0.378 0.386 e 0.650 0.026 E 6.300 6.500 0.248 0.256 E1 4.300 4.500 0.169 0.177 L 0.450 0.750 0.018 0.030 U 4.410 5.510 0.174 0.217 V 2.400 3.000 0.094 0.118 U 5.500 6.170 0.217 0.243 V 1.600 2.210 0.063 0.087 Option 1 Option 2 28-Lead TSSOP (Exposed Pad) Plastic 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. www.richtek.com 12 DS8566-03 November 2013