® RT8543A 6-String 43V White LED Driver with Boost Regulator General Description Features The RT8543A is a high efficiency white LED driver. It is designed for LCD panel that employs an LED array as the lighting source. An integrated switch current mode Boost controller drives six strings in parallel and supports up to 10 pieces of LEDs per string. The internal current sinks support maximum ±2% current matching for excellent brightness uniformity in each LED string. To provide enough headroom for the operating of current sink, Boost controller monitors the minimum voltage of feedback pins and regulates an optimized output voltage for power efficiency. Wide Input Voltage : VIN 2.5V to 24V High Output Voltage : VOUT up to 43V Current Mode Boost Regulator 600kHz to 1.2MHz Switching Frequency Up to 85% High Frequency Adjustable Full Channel Current from 5mA to 50mA and Matched to 2% Channel Current Regulation with ±3% Accuracy Dimming Controls Direct PWM Dimming up to 20kHz and Minimum On-Time to 500ns PWM to Analog Dimming up to 20kHz with 8 bit resolution Built-In Soft-Start to Prevent Inrush Current without External Capacitor Disconnects LED in Shutdown Protection Strings Open Detection Current Limit Protection Adjustable Over-Voltage Protection Over-Temperature Protection 20-Lead WQFN Package RoHS Compliant and Halogen Free The RT8543A has wide input voltage range from 2.5V to 24V and provides adjustable 5mA to 50mA LED current. The internal 200mΩ, 43V power switch with current-mode control provides cycle-by-cycle over-current protection. The RT8543A also integrates PWM and analog dimming functions for accurate LED current control. The input PWM dimming frequency can operate from 100Hz to 20kHz without inducing any inrush current in LED or inductor. The RT8543A is available in thin WQFN-20L 4x4 package. Applications UMPC and Notebook Computer Backlight Simplified Application Circuit D1 L1 VIN VOUT COUT CIN LX VIN Enable RT8543A OVP EN ROVP1 PWM PWM Signal COMP CC RCOMP CCOMP ISET FREQ RISET RFSW December 2015 : : : : : : : : : : : : : : : : : : LED1 LED2 LED3 LED4 LED5 LED6 AGND PGND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 ROVP2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8543A Ordering Information Pin Configurations RT8543A COMP VIN VDC PWM LX (TOP VIEW) Package Type QW : WQFN-20L 4x4 (W-Type) (Exposed Pad-Option 1) 20 19 18 17 16 EN FREQ ISET MODE AGND Lead Plating System G : Green (Halogen Free and Pb Free) Note : 1 15 2 14 4 13 12 11 7 8 9 10 LED6 LED5 LED4 LED3 LED2 6 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. 21 5 Richtek products are : GND 3 LX PGND PGND OVP LED1 WQFN-20L 4x4 Suitable for use in SnPb or Pb-free soldering processes. Marking Information 45= : Product Code 45=YM DNN YMDNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function Enable Control Input (Active High). There is an internal 400k pull-low resistor connected to AGND. 1 EN 2 FREQ 3 ISET 4 MODE Mode Selection Pin. Floating the MODE pin for PWM dimming mode. Connecting the MODE pin to GND for mixed mode. Connecting the MODE pin to VDC for pure DC mode. 5 AGND Analog Ground of LED Driver. LED6 to LED1 Current Sink for LED String. (Leav e the pin floating or short to GND, if not used.) OVP Over-Voltage Protection for Boost Converter. The detecting threshold is 1.2V. 13, 14 PGND Power Ground of Boost Converter. 15, 16 LX The Switching for Boost Converter. 17 PWM PWM Dimming Control Input. 18 VDC Internal Regulator Voltage. Connect a capacitor to ground or floating. 19 VIN Power Supply Input for LED Driver. 20 COMP Compensation Node for Boost Converter. Connect a compensation network to ground. GND The Exposed Pad must be Soldered to a Large PCB and Connected to GND for Maximum Power Dissipation. 6, 7, 8, 9, 10, 11 12 21 (Exposed Pad) Switching Frequency of Boost Converter Setting Input. Connect a resistor to ground. LED Current Setting. LED current is set by the value of the resistor RISET connected from the ISET pin to ground. VISET is typically 1V. ILED mA 1000 RISET k Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Function Block Diagram VIN VDC OVP FREQ + 1.2V - OSC EN LDO Q R Q OCP + + PWM Controller OTP PGND + COMP PWMO Generator PWM-to-DC MUX PWM S LX GND 0.5V 6 Mini LED Selection LED Open Detection MODE LED1 LED2 …… DAC LED6 + - + + - - …… + - ISET AGND Operation Enable Control When VIN is higher than the UVLO voltage and the EN pin input voltage is higher than rising threshold, the VDC will be regulated around 3.8V if VIN is higher than 3.8V. OSC The switching frequency is adjustable by the external resistor connected between the FREQ pin and GND. the LX N-MOSFET will be turned off until the temperature is lower than the 120°C (typically). OVP When the OVP pin voltage is higher than 1.2V, the LX N-MOSFET is turned off immediately to protect the LX N-MOSFET. Minimum LED Selection PWM Controller This controller includes some logic circuit to control LX N-MOSFET on/off. This block controls the minimum ontime and max duty of LX. This block detects all LEDx voltage and select a minimum voltage to EA (Error Amplifier). This function can guarantee the lowest of the LED pin voltage is around 600mV and Vout can be Boost to the highest forward voltage of LED strings. 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. That OCP > 2.5A and keeps 2ms, IC will be shutdown. When the junction temperature is higher than 150°C (typically), Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 LED Open Detection If the voltage at LEDx pin is lower than 100mV, this channel is defined as open channel and the Minimum LED Selection function will discard it to regulate other used channels in proper voltage. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8543A Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN to GND -----------------------------------------------------------------------------------EN, PWM, ISET, COMP, MODE, FREQ to GND -----------------------------------------------------------------LX, OVP, LED1 to LED6 to GND --------------------------------------------------------------------------------------VDC to GND ---------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 26.5V −0.3V to 26.5V −0.3V to 48V −0.3V to 7V WQFN−20L 4x4 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN−20L 4x4, θJA -----------------------------------------------------------------------------------------------------WQFN−20L 4x4, θJC -----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- 3.57W Recommended Operating Conditions 28°C/W 7°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.5V to 24V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 5V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max IVIN PWM = COMP = 0V, Not Switching -- 3 -- IVIN_SW PWM = COMP = 2V, Switching -- 4 -- VIN Shutdown Current ISHDN VIN = 4.5V, EN = 0V -- -- 10 VIN Under-Voltage Lockout Threshold VUVLO VIN Rising 2.1 2.3 2.5 Hysteresis 0.1 0.2 0.3 Logic-High VIH VIN = 2.5V to 24V 1.3 -- -- Logic-Low VIN = 2.5V to 24V -- -- 0.7 RfSW = Open -- 0.6 -- RfSW = 110k -- 0.8 -- RfSW = 59k -- 1 -- RfSW = 38.2k -- 1.2 -- VIN > 4.5V -- 0.2 -- VIN Quiescent Current Unit mA A V Control Input EN, PWM, MODE Input Voltage VIL V Boost Converter Switching Frequency LX On-Resistance (N-MOSFET) fSW RLX Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 MHz is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Parameter Symbol Test Conditions Min Typ Max Unit Minimum On-Time TMON f SW = 1MHz -- 80 -- ns Maximum Duty DMAX f SW = 600kHz 88 91 96 % LX Current Limit ILIM 2.2 2.5 2.8 A Regulated VLEDx VLEDx Highest LED String, ILED = 20mA -- 0.5 -- V ISET = 20mA, MODE = PWM Mode 3 -- 3 % ISET = 20mA, MODE = Mixed Mode, PWM Duty < 25% ISET = 20mA, MODE = Mixed Mode, PWM Duty = 25% to 100% MODE = Pure DC Mode PWM Duty = 15% to 100% ISET = 20mA, MODE = Pure DC Mode PWM Duty = 5% to 15% 8 -- 8 % 5 -- 5 % 8 -- 8 % ISET = 20mA, MODE = Pure DC Mode PWM Duty = 1% to 5% 10 -- 10 % ISET = 20mA, MODE = PWM Mode 2 -- 2 % ISET = 20mA, MODE = Mixed Mode, PWM Duty < 25% 2 -- 2 % ISET = 20mA, MODE = Mixed Mode & Pure DC Mode, PWM Duty = 25% to 100% 2 -- 2 % ISET = 20mA, MODE = Pure DC Mode, PWM Duty = 5% to 25% 2 -- 2 % ISET = 20mA, MODE = Pure DC Mode, PWM Duty = 1% to 5% 5 -- 5 % VISET -- 1 -- V OVP Threshold VOVP 1.16 1.2 1.24 V OVP Fault Threshold VOVPF -- 50 -- mV Thermal Shutdown Temperature TSD -- 150 -- C LED Pin Under-Voltage Threshold VLSD -- 0.1 -- V LED Current Programming LED Current Accuracy (ILEDx ISET) / ISET x 100% Current Balance Between CSx (ICSx IAVG) / IAVG x 100% ISET Pin Voltage ILEDA ILEDM Fault Protection Un-Connection 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 © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8543A Typical Application Circuit L1 10µH VIN 5V to 24V CIN 4.7µF C1 1µF CEN 10nF RT8543A OVP 12 17 CC VDC PWM LED1 LED2 LED3 LED4 LED5 LED6 3 ISET 2 FREQ RISET 49.9k COVP 47pF EN 20 COMP RCOMP 5.1k CCOMP 22nF ROVP2 1M ROVP1 MODE CPWM 10nF PWM Signal 15, 16 LX 19 VIN 1 RPWM 10k VOUT 43V MAX COUT 4.7µF R1 100 REN 10k Enable D1 SS26 RFSW NC 4 : : : : : : : : : : : : : : : : : : CDC 1µF 18 11 10 9 8 7 6 AGND PGND GND 5 13, 14 21 (Exposed Pad) Figure 1. For General Application Circuit L1 10µH VIN 2.5V to 24V D1 SS14 R1 100 VAVDD 5V 19 VIN C1 1µF Enable 1 CEN 10nF RT8543A OVP 12 EN MODE RPWM 10k VDC 17 CPWM 10nF PWM Signal 15, 16 LX PWM 20 COMP CC RCOMP 5.1k CCOMP 22nF RISET 49.9k ROVP2 1M ROVP1 REN 10k 3 ISET 2 FREQ RFSW NC VOUT 25V MAX (VOUT depends on DMAX) COUT 4.7µF CIN 4.7µF LED1 LED2 LED3 LED4 LED5 LED6 4 18 COVP 47pF : : : : : : : : : : : : : : : : : : CDC 1µF 11 10 9 8 7 6 AGND PGND GND 5 13, 14 21 (Exposed Pad) Figure 2. For Low Input Voltage Application Circuit Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Typical Operating Characteristics LED Driver Efficiency LED Current vs. Input Voltage 100 22 CH1 CH2 CH3 CH4 CH5 CH6 LED Current (mA) Efficiency (%) 80 60 40 21 20 19 20 VIN = 12V, LEDs = 10S6P, RISET = 49.9kΩ VIN = 12V, RISET = 49.9kΩ 0 18 0 10 20 30 40 50 60 70 80 90 100 4 8 Dimming Duty (%) LED Current vs. PWM Duty Cycle 20 24 OVP Threshold Voltage vs. Input Voltage OVP Threshold Voltage (V) 1.5 16 PWM = 100Hz PWM = 1kHz PWM = 10kHz PWM = 20kHz 12 8 4 1.4 1.3 1.2 1.1 VIN = 12V, RISET = 49.9kΩ VIN = 12V, RISET = 49.9kΩ 0 1.0 0 20 40 60 80 100 4 8 PWM Duty Cycle (%) 12 16 20 24 Input Voltage (V) Quiescent Current vs. Input Voltage LED Current vs. Temperature 2.5 Quiescent Current (mA) 22 LED Current (mA) 16 Input Voltage VIN (V) 20 LED Current (mA) 12 21 20 19 2.3 2.0 1.8 No Switching VIN = 12V, RISET = 49.9kΩ 1.5 18 -50 -25 0 25 50 75 100 Temperature (C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 125 2.5 7.0 11.5 16.0 20.5 25.0 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8543A Power On from EN LED Line Transient Response EN (5V/Div) VIN (5V/Div) VLED (20V/Div) I LED (10mA/Div) LX (20V/Div) I IN (500mA/Div) VIN = 5V to 13V, RISET = 49.9kΩ Time (50ms/Div) Time (5ms/Div) Power On PWM Mode Power On Mixed Mode1 VIN (10V/Div) EN (5V/Div) PWM (5V/Div) VIN (10V/Div) EN (5V/Div) I LED (50mA/Div) I LED (100mA/Div) PWM (5V/Div) VIN = 12V, 60 LEDs, RISET = 49.9kΩ VIN = 12V, 60 LEDs, RISET = 49.9kΩ Time (10ms/Div) Time (10ms/Div) Power On Mixed Mode2 Power On Mixed Mode3 VIN (10V/Div) EN (5V/Div) VIN (10V/Div) EN (5V/Div) PWM (5V/Div) PWM (5V/Div) I LED (100mA/Div) I LED (100mA/Div) VIN = 12V, 60 LEDs, RISET = 49.9kΩ Time (10ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, 60 LEDs, RISET = 49.9kΩ VIN = 12V, 60 LEDs, RISET = 49.9kΩ Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Application Information The RT8543A is a general purpose 6-CH LED driver capable of delivering an adjustable 5mA to 50mA LED current. The IC is a current mode Boost converter integrated with a 43V/2.5A power switch and can cover a wide VIN range from 2.5V to 24V. The part integrates built-in soft-start with PWM dimming control provides over voltage, over temperature and current limit protection features. It also integrates PWM and mixed mode dimming function for accurate LED current control. The PWM dimming frequency can operate from 100Hz to 20kHz without inducing any inrush current in LED or inductor. LED Driver Inductor Selection LED Power Soft-Start Function IOUT is the sum of current from all LED strings. The period from EN is enabled to LED current rises, is several tens of milliseconds according to the brightness dimming mode (PWM Mode or Mixed Mode). The LED current starts up after VIN, PWM and EN signals are all ready. The RT8543A supports soft-start function to reduce inrush current, and the soft-start inrush peak current must be less than 2.5A. The LED Boost converter operates in DCM over the entire input voltage range when the inductor value L1 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 saturation current rating greater than the peak current calculated by the following equation : VOUT IOUT VIN TSW VOUT VIN IPEAK VIN 2 L VOUT LED Driver 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, CC and CCOMP, will adjust the zero and pole respectively to maintain stability. Moreover, the resistor, RCOMP, will adjust the mid-band gain for fast transient response. Setting and Regulation of LED Current The LED current can be calculated by the following equation : ILED 1000 (mA) RISET where, RISET is the resistor between the ISET pin and GND. This setting is the reference for the LED current at LED1 to LED6 and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 The value of the inductor (L) calculated by the following equation determines the criteria of the transition from DCM to CCM mode : L VOUT VIN VIN2 2 IOUT fSW VOUT 2 where, VOUT is the maximum output voltage. VIN is the minimum input voltage. fSW is the switching frequency. LED Driver Diode Selection 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. LED Driver Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most applications, a 4.7μF 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 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8543A capacitor based on the output voltage ripple requirements. The minimum value of the output capacitor, COUT, can be calculated by the following equation : COUT 100% 50% PWM Mode / Mixed Mode and Pure DC Mode Brightness Dimming The RT8543A allows three ways of LED brightness control. T OA Figure 3. LED Current Control Using PWM Dimming Mode (MODE = Floating) Duty = 100% Duty = 90% Duty = 10% Duty = 50% Duty = 100% Duty = 50% PWM 100% ISET 100% ISET 90% ISET 50% ISET 50% ISET IOUT 25% ISET Figure 4. LED Current Control Using Mixed Dimming Mode (MODE = GND) (b) PWM Duty < 25%, the DC dimming will translate to DC-PWM dimming to control the LED current. In this state, the LED current is fixed at 0.25 x ISET, and the dimming duty is 4 x PWM duties. The minimum D/A converter is 512 steps resolution for ISET regulation. T IOUT (a) When 25% ≤ PWM duty ≤ 100%, the current source outputs are DC dimming, and the PWM duty cycle modulates the amplitude of the currents. Pure DC Mode Dimming : If the MODE pin is set to VDC, the PWM and IOUT will delay by two periods. First cycle delay is required for the period, while the second cycle delay is for the duty rate calculation. 12.5% ISET PWM Mode Dimming : When the MODE pin is set to float, the dimming mode operates in PWM Mode (Figure 3). During the PWM dimming, the current source turn-on/ off is synchronized with the PWM signal. The LED current frequency is equivalent to PWM input frequency. Mixed Mode Dimming : If the MODE pin is set to GND, the dimming mode operates in Mixed Mode (Figure 4). In this mode, the PWM and IOUT dimming cycle will delay by two periods. First cycle delay is required for the period, while the second cycle delay is for the duty rate calculation. 25% PWM VOUT VIN IOUT VRIPPLE VOUT fSW 30% Duty = 100% Duty = 90% Duty = 10% Duty = 50% Duty = 100% Duty = 50% PWM 100% ISET 100% ISET 90% ISET 50% ISET 50% ISET IOUT 10% ISET Figure 5. LED Current Control Using Pure DC Dimming Mode (MODE = VDC) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Brightness Control The RT8543A features the digital dimming control scheme. A very high contrast ratio true digital PWM dimming can be achieved by driving PWM pin with a the PWM signal and the recommended PWM frequency is 100Hz to 10kHz. Dimming frequency can be sufficiently adjusted from 100Hz to 20kHz. However, LED current cannot be 100% proportional to duty cycle especially for high frequency and low duty ratio because of physical limitation caused by inductor rising time. Please refer to below Table. VIN 2.3V UVLO 2.1V EN Soft-Start VOUT IOUT Figure 6. LED UVLO Function Table. Input PWM Dimming Frequency vs Minimum Duty ( Mixed, PWM and DC Dimming Mode) VIN PWM Input Dimming Frequency Duty (Min) Duty (Max) 120Hz to 8kHz 0.6% 100% 8.1kHz to 11kHz 0.7% 100% 11.1kHz to 14kHz 0.8% 100% 14.1kHz to 17kHz 0.9% 100% 17.1kHz to 20kHz 1% 100% Note : The minimum duty in Table is based on the application circuit and does not consider the deviation of current linearity when fPWM > 10kHz, ILED may not achieve setting current in duty (min.) due to different VOUT / VIN ratio at VIN = 12V. LED Driver Under Voltage Lockout (UVLO) The UVLO circuit compares the LED driver input voltage at VIN with the UVLO threshold (2.3V rising, typ.) to ensure the input voltage is high enough for reliable operation. The 200mV (typ.) hysteresis prevents supply transients from causing a shutdown. Once VIN exceeds the UVLO rising threshold, the LED soft-start will begin after a delay time around several milliseconds. When VIN falls below the UVLO falling threshold, the controller turns off all LED driver functions. EN PWM VOUT IOUT Figure 7. LED Driver Power On Sequence (PWM Mode) VIN PWM EN Soft-Start VOUT ISET x Duty IOUT Figure 8. LED Driver Power On Sequence (Mixed Mode) VIN PWM 20ms EN Soft-Start VOUT ISET Duty x ISET IOUT Figure 9. LED Driver Power On Sequence (Mixed Mode; Duty = 100%) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8543A If at least one channel is in normal operation, the LED driver will automatically ignore the open channels and continue to regulate current for the channels in normal operation. LED Driver Over Voltage Protection The LED driver equips an Over Voltage Protection (OVP) function. When the voltage at the OVP pin reaches a threshold of approximately 1.2V, the driver will turn off. The drivers turn on again once the voltage at OVP drops below the threshold voltage. Thus, the output voltage can be clamped at a certain voltage level. This voltage level can be calculated by the following equation : R VOUT, OVP VOVP 1 OVP2 ROVP1 where ROVP1 and ROVP2 are the resistors in the voltage divider connected to close to the OVP pin. It is suggested to use 400kΩ to1MΩ for ROVP2 to reduce loading effect. Over Temperature Protection The RT8543A includes an Over Temperature Protection (OTP) feature to prevent overheating due to excessive power dissipation from damaging the device. The OTP function will shut down LED driver when the junction temperature exceeds 150°C. It will reactivate the device when powered on again. To maintain continuous operation, the junction temperature should be kept below 125°C. Thermal Considerations For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-20L 4x4 package, 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-20L 4x4 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 10 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Maximum Power Dissipation (W)1 LED Channel Open Circuit Protection Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 10. Derating Curve of Maximum Power Dissipation 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS8543A-01 December 2015 RT8543A Layout Considerations PCB layout is very important to design power switching converter circuits. The following layout guide lines should be strictly followed for best performance of the RT8543A. The power components L1, D1, CIN and COUT must be placed as close as possible to reduce the ac current loop. The PCB trace between power components must be short and wide as possible due to large current flow through these trace during operation. Place L1 and D1 connected to LX pins as close as possible. The trace should be short and wide as possible. It is recommend to place C1 close to VIN pin. Pin 20 is the compensation point to adjust system stability. Place the compensation components to pin 20 as close as possible. Place the power components as close as possible. The traces should be wide and short especially for the high-current loop. Locate the C1 as close to VIN as possible. VIN GND CIN GND L1 D1 CCOMP RCOMP 20 19 18 17 COMP VIN VDC PWM C1 Locate the RISET as close to ISET as possible. 1 16 COUT EN LX 15 PGND 14 2 FREQ GND RISET 3 GND ISET PGND 13 LED2 LED1 11 LED3 5 AGND LED4 OVP 12 LED5 4 MODE LED6 GND VOUT R1 LX The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. 6 7 8 9 10 Figure 11. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS8543A-01 December 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8543A 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 D2 E2 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 0.300 0.006 0.012 D 3.900 4.100 0.154 0.161 Option 1 2.650 2.750 0.104 0.108 Option 2 2.100 2.200 0.083 0.087 E 3.900 4.100 0.154 0.161 Option 1 2.650 2.750 0.104 0.108 Option 2 2.100 2.200 0.083 0.087 e 0.500 L 0.350 0.020 0.450 0.014 0.018 W-Type 20L QFN 4x4 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 14 DS8543A-01 December 2015