® RT8576A High Voltage 4-CH LED Driver with PWM Dimming General Description Features The RT8576A is an 4-CH LED driver capable of delivering 120mA for each channel. The RT8576A 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. z Wide Input Supply Voltage Range : 9V to 28V z Adjustable Boost Controller Switching Frequency from 100kHz to 1MHz Programmable Channel Current up to 180mA Channel Current Matching : 1.5% External Dimming Control Boost MOSFET Over-Current Protection Automatic LED Open/Short Protection VIN Under-Voltage Lockout Adjustable Over-Voltage Protection Thermal Shutdown Protection Abnormal State Indicator for OVP/Short/Thermal Condition RoHS Compliant and Halogen Free The PWM output voltage loop selects and regulates the LED strings with the highest voltage, hence, it allows voltage mismatches between LED strings. The RT8576A automatically detects and disconnects any unconnected and/or broken strings during operation from PWM loop to prevent VOUT from over voltage. z z z z z z z z z The 1.5% matched LED currents on all channels are simply programmed with a resistor. PWM dimming is implemented with external PWM input signal. When an abnormal situation (OVP/short/thermal) occurs, a state signal will be sent to the system to shut down the IC. z Applications z z z LCD TV, Monitor Display Backlight LED Driver Application General Purpose Constant Current Source Simplified Application Circuit L1 VIN 9V to 28V CIN D1 ROVP2 R1 OVP VIN CVIN RLDR MSW RF External/Internal PWM Enable RT8576A ISW RPWM RENA ROVP1 LDR CF RSENSE PWM ENA GND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 VOUT(MAX) 55V ISEN1 ISEN2 ISEN3 ISEN4 STATUS ISET RT RISET COUT : : : : : : : : : : : : : : : : FLT RRT is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8576A Ordering Information Pin Configurations (TOP VIEW) RT8576A Package Type CP : TSSOP-16 (Exposed Pad) S : SOP-16 SP : SOP-16 (Exposed Pad) N : DIP-16 Lead Plating System G : Green (Halogen Free and Pb Free) Note : 15 3 14 4 GND 5 6 17 13 12 11 7 10 8 9 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` PWM SSTCMP STATUS VIN VREF LDR ISW ENA 16 2 TSSOP-16 (Exposed Pad) Richtek products are : ` ISEN1 ISEN2 GND ISEN3 ISEN4 ISET OVP RT Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT8576AGCP ISEN4 ISET OVP RT ENA ISW LDR VREF 15 3 14 4 13 5 12 6 11 7 10 8 9 RT8576AGCP : Product Number RT8576A GCPYMDNN RT8576AGS : Product Number RT8576A GSYMDNN SOP-16 YMDNN : Date Code RT8576AGS YMDNN : Date Code ISEN3 GND ISEN2 ISEN1 PWM SSTCMP STATUS VIN 16 2 ISEN4 ISET OVP RT ENA ISW LDR VREF ISEN3 GND ISEN2 ISEN1 PWM SSTCMP STATUS VIN 16 2 15 3 14 4 5 GND 13 12 6 17 11 7 10 8 9 SOP-16 (Exposed Pad) RT8576AGSP RT8576AGSP : Product Number RT8576A GSPYMDNN YMDNN : Date Code RT8576AGN RichTek RT8576A GNYMDNN RT8576AGN : Product Number YMDNN : Date Code ISEN4 16 ISEN3 OVP 2 15 GND ISET 3 14 ISEN2 RT 4 13 ISEN1 ENA 5 12 PWM ISW 6 11 SSTCMP LDR 7 10 STATUS VREF 8 9 VIN DIP-16 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Functional Pin Description Pin No. Pin Name TSSOP-16 SOP-16 SOP-16 DIP-16 (Exposed Pad) (Exposed Pad) Pin Function 1 13 13 13 ISEN1 LED1 Current Sink. Leave the pin unconnected if it is not used. 2 14 14 14 ISEN2 LED2 Current Sink. Leave the pin unconnected if it is not used. 3, 17 (Exposed Pad) 15 15, 17 (Exposed Pad) 15 GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation. 4 16 16 16 ISEN3 LED3 Current Sink. Leave the pin unconnected if it is not used. 5 1 1 1 ISEN4 LED4 Current Sink. Leave the pin unconnected if it is not used. 6 2 2 3 ISET A resistor or a current from DAC on this pin programs the full LED current. 7 3 3 2 OVP Over-Voltage Protection. PWM Boost converter turns off when VOVP goes higher than 2V. 8 4 4 4 RT Switching Frequency Setting. Connect a resistor between RT and GND to set the Boost converter switching frequency. 9 5 5 5 ENA Enable Control Input. When pulled low, chip is in shutdown mode. 10 6 6 6 ISW 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 ev ery switching cycle. 11 7 7 7 LDR Boost Conv erter Power Switch Gate Output. This pin drives the external power N-MOSFET device. 12 8 8 8 VREF 1μF capacitor should be placed on this pin to stabilize the 5V output of the internal regulator. This regulator is for chip internal use only. 13 9 9 9 VIN Power Supply of the Chip. For good bypass, a low ESR capacitor is required. 14 10 10 10 STATUS Boost Converter Operation Status Output. 15 11 11 11 SSTCMP PWM Boost Conv erter Loop Compensation Node. 16 12 12 12 PWM Dimming Control. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8576A Function Block Diagram STATUS LDR ISW RT OSC VIN - 8V OVP OTP S + R OVP + 2V - SSTCMP + VREF Shutdown + - 1.2V ISEN1 + 5V LDO 5V ………………… ENA LED Short R - ISEN4 VOUT Regulation Unit + - + - GND PWM ISET Operation The RT8576A integrated a current-mode Boost PWM controller and 4 LED drivers. When ENA and PWM are high and VIN is higher than the UVLO threshold voltage, the controller starts operation. In normal operation, the LDR pin turns high when the gate driver is set by the oscillator and the LDR pin turns low when the gate driver is reset by the current comparator. When the LDR pin turns high to turn on the external MOSFET, the inductor current will rise up. Once the ISW pin voltage reaches the level of the SSTCMP pin, the current comparator will reset the gate driver and turn off the MOSFET. The LDR pin is then set to high again by OSC and repeats in the next switching cycle. The oscillator frequency can be set by an external resistor at the RT pin. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 The output voltage of the Boost converter supports LED current and regulation voltage at the ISENx pin. The LED current is set by an external resistor at the ISET pin. A PWM dimming function is provided to control the LED brightness through the PWM pin. If OVP, OTP or shorted LED happens, the STATUS pin will be pulled to low as a fault indicator. is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Absolute Maximum Ratings z z z z z z z z z (Note 1) Supply Voltage, VIN, STATUS -----------------------------------------------------------------------------------------ISEN1 to ISEN4 ----------------------------------------------------------------------------------------------------------PWM, ENA, LDP, ISW, SSTCMP, RT, VREF, OVP, ISET ------------------------------------------------------Power Dissipation, PD @ TA = 25°C TSSOP-16 (Exposed Pad) ---------------------------------------------------------------------------------------------SOP-16 ---------------------------------------------------------------------------------------------------------------------SOP-16 (Exposed Pad) -------------------------------------------------------------------------------------------------DIP-16 -----------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSSOP-16 (Exposed Pad), θJA ----------------------------------------------------------------------------------------TSSOP-16 (Exposed Pad), θJC ---------------------------------------------------------------------------------------SOP-16, θJA ----------------------------------------------------------------------------------------------------------------SOP-16, θJC ---------------------------------------------------------------------------------------------------------------SOP-16 (Exposed Pad), θJA -------------------------------------------------------------------------------------------SOP-16 (Exposed Pad), θJC -------------------------------------------------------------------------------------------DIP-16, θJA -----------------------------------------------------------------------------------------------------------------DIP-16, 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 z z z z z z 33V 60V 5.5V 3.39W 0.92W 3.38W 1.68W 29.5°C/W 7.4°C/W 108.6°C/W 27.1°C/W 29.5°C/W 2.9°C/W 59.6°C/W 7.6°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Voltage, VIN -----------------------------------------------------------------------------------------------------ISEN1 to ISEN4 ----------------------------------------------------------------------------------------------------------IISEN1 to IISEN4 --------------------------------------------------------------------------------------------------------------Switching Frequency Range -------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------------Ambient Temperature Range -------------------------------------------------------------------------------------------- 9V to 28V 55V 20mA to 120mA 100kHz to 1MHz −40°C to 125°C −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Voltage Supply Current IVIN Switching Off -- 2 5 mA Shutdown Current ISHDN VENA = 0V -- 4.5 10 μA VDD LDO Output VREF 4.5 5 5.5 V VDD LDO Source Current IREF -- -- 30 mA Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8576A Parameter VIN UVLO Threshold ENA Input Voltage Symbol VUVLO Test Conditions Min Typ Max VIN Rising -- 6.5 8 Hysteresis 0.8 1.4 1.8 Unit V Logic-High VENAH 1.5 -- -- Logic-Low VENAL -- -- 0.8 57 60 63 mA -- ±1.5 ±3 % V LED Current Programming LED Current Accuracy RISET = 20kΩ, VPWM = 3.3V LED Current Matching Δ=± ISEN1 to ISEN4 Regulation Voltage ILED = 60mA 0.76 0.86 0.96 V VLED Threshold No Connection 0.08 0.14 0.2 V ILED(MAX) − ILED(MIN) 2 × ILED(AVG) × 100% Dimming PWM Input Voltage Logic-High VPWMH 1.2 -- -- Logic-Low VPWML -- -- 0.4 160 200 240 kHz V PWM Boost Controller Switching Frequency fOSC Minimum On Time tON -- 100 -- ns Maximum Duty Cycle Dmax 80 -- -- % 0.35 0.45 0.6 V Gate Driver Source 1 2.5 -- A Gate Driver Sink 1 3.3 -- A 1.9 2 2.1 V 6.2 7 7.9 V ISW Current Sense Limit RRT = 215k Input Current Limit OVP, SCP, OTP OVP Threshold VOVP SCP Threshold VSCP ISEN1 to ISEN4 Thermal Shutdown Temperature TSD Lockout Temperature Point -- 150 -- °C Thermal Shutdown Hysteresis ΔTSD 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. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Typical Application Circuit L1 22µH VIN 9V to 28V CIN 20µF D1 R1 10 OVP VIN CVIN 1µF MSW LDR RF 100 RSENSE 100m External/Internal PWM Enable RENA 1k RSSTCMP 560 CSSTCMP 0.22µF : : : : : : : : : : : : ISEN1 ISEN3 ISEN4 RSTATUS 100k STATUS VIN FLT PWM ENA ISET RT GND RISET 20k RRT 56k RREF 10k SSTCMP Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 : : : : COUT 4.7µF x 6 ISEN2 ISW CF 1nF RPWM 1k ROVP2 3.6M ROVP1 130k RT8576A RLDR 5 VOUT(MAX) 55V VREF CREF 1µF is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8576A Typical Operating Characteristics LED Current vs. Input Voltage Efficiency vs. Input Voltage 100 80 75 LED Current (mA) Efficiency (%) 90 80 70 60 70 65 60 ISEN1 ISEN2 ISEN3 ISEN4 55 50 16LEDs per-channel, PWM = 3.3V, RISET = 20kΩ, fOSC = 500kHz 45 16S4P, PWM = 3.3V, ILEDx = 60mA, fOSC = 500kHz 50 40 9 11 13 15 17 19 21 23 25 27 29 9 11 13 15 Input Voltage (V) 75 6.5 70 6.0 65 5.5 VREF (V) LED Current (mA) 7.0 60 ISEN1 ISEN2 ISEN3 ISEN4 50 16S4P, VIN = 12V, PWM = 3.3V, RISET = 20kΩ, fOSC = 500kHz 23 25 27 29 5.0 4.5 3.5 -20 0 20 40 60 80 VIN = 12V 3.0 40 -50 100 -25 0 25 50 75 100 125 Temperature (°C) Temperature (°C) LED Current vs. Dimming Duty OVP Threshold vs. Input Voltage 60 3.0 2.8 OVP Threshold (V) 50 LED Current (mA) 21 4.0 45 -40 19 VREF vs. Temperature LED Current vs. Temperature 80 55 17 Input Voltage (V) 200Hz 1kHz 10kHz 40 30 20 10 16S4P, VIN = 12V, fOSC = 1MHz 0 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0 20 40 60 80 Dimming Duty (%) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 100 9 11 13 15 17 19 21 23 25 27 29 Input Voltage ( V ) is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Quiescent Current vs. Input Voltage Quiescent Current vs. Temperature 4.0 3.5 2.35 Quiescent Current (mA) Quiescent Current (mA) 2.40 2.30 2.25 2.20 2.15 3.0 2.5 2.0 1.5 1.0 0.5 VIN = 12V 2.10 VIN = 12V 0.0 9 11 13 15 17 19 21 23 25 27 29 -50 Input Voltage (V) -25 0 25 50 75 100 125 Temperature (°C) fOSC vs. RRT Line Transient Response 1000 900 800 f OSC (kHz) 700 VIN (10V/Div) 600 500 IOUT (1A/Div) 400 300 200 VIN = 10.8V to 13.2V, WM = 3.3V, RISET = 20kΩ, fOSC = 500kHz 100 0 0 50 100 150 200 250 300 350 Time (10ms/Div) RRT (kΩ) Power On from PWM Power On from EN VIN = 12V, fOSC = 500kHz VOUT (50V/Div) VOUT (50V/Div) VPWM (5V/Div) VEN (5V/Div) VLX (50V/Div) VLX (50V/Div) I LED (50mA/Div) I LED (50mA/Div) Dimming Duty = 50%, fDimming = 200Hz Time (5ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 VIN = 12V, PWM = 3.3V, fOSC = 500kHz Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8576A Application information The RT8576A is an 4-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 RT8576A 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 RT8576A integrates adjustable switching frequency and provides circuitry for over-temperature, LED short-circuit, overvoltage and current limit protection. VREF Capacitor Selection The RT8576A equips a built-in LDO linear regulator to provide the internal gate driver of IC power. The output of LDO is the pin out of VREF. The VREF pin is recommended to connect at least a 1μF/25V ceramic capacitor. The VREF capacitor should be X5R or X7R type for stable operating voltage range and temperature range. Compensation The regulator loop can be compensated by adjusting the external components connected to the SSTCMP pin. The SSTCMP pin is the output of the internal error amplifier. The compensation capacitor will adjust the zero to maintain stability and the resistor value will adjust the compensator gain for fast transient response. Typical values of the compensation components are RSSTCMP = 560Ω, CSSTCMP = 0.22μF. where RISET is the resistor between the ISET pin and GND. This setting is the reference for the LED current at pin ISENx and represents the sensed LED current for each string. The DC/DC converter regulates the LED current according to the setting. Over-Voltage Protection The RT8576A integrates Over-Voltage Protection (OVP). When the voltage at the OVP pin rises above the threshold voltage of approximately 2V, the internal switch will be turned on and the STATUS pin will be pulled low. The internal switch will be turned on again once the voltage at the OVP 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 × ⎜ 1 + OVP2 ⎟ ROVP1 ⎠ ⎝ where ROVP1 and ROVP2 are the resistors in the resistive 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 strings in normal operation. Suggested value for ROVP2 is up to 3MΩ to prevent loading effect. LED Short-Circuit Protection The RT8576A integrates LED Short-Circuit Protection (SCP). If one of the ISEN1 to ISEN4 pin voltages exceeds a threshold of approximately 7V during normal operation, the STATUS pin will be pulled to low for a fault signal. LED Connection STATUS The RT8576A equips 4-CH LED drivers and each channel supports up to 18 LEDs. The LED strings are connected from the output of the Boost converter to pin ISENx (x = 1 to 4) respectively. If one of the LED channel is not in use, the ISENx pin should be opened directly. The STATUS is pulled to high at normal state. After the IC is enabled, STATUS will output logic low if LED short/ OVP/OTP conditions exist. STATUS will be reset after VIN or ENA is re-applied. Setting and Regulation of LED current The RT8576A switching frequency is programmable from 100kHz to 1MHz by adjusting the oscillator resistor, RRT. The LED current can be calculated by the following equation : ILED ≅ 1200 RISET Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Setting the Switching Frequency The switching frequency can be calculated by the following equation : 21.6 × 109 fSW ≅ 100k + RRT is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Current Limit Protection Brightness Control The RT8576A can sense the RSENSE voltage between the ISW pin and GND to achieve over-current protection. The Boost converter senses the inductor current during the on period. When the peak current value of inductor current is larger than the current limit value, the internal switch (LDR) will be closed. In the off-period, the inductor current will decrease until the internal gate driver is turned on by the oscillator. The current limit value can be calculated by the following equation : 0.45V Current Limit (A) ≅ RSENSE The RT8576A 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. Power on/off Sequence LED driver is without power sequence concern. Mode1, Mode2 and Mode3 are different power sequences respectively. There is no concern in the above condition. VIN Over-Temperature Protection The RT8576A 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 low when junction temperature exceeds 150°C. Main converter starts switching after junction temperature cools down by approximately 20°C. VIN VOUT VOUT EN EN PWM PWM Power On Mode1 Power Off Mode1 VIN VIN VOUT VOUT EN EN PWM PWM Power On Mode2 Power Off Mode2 VIN VIN UVLO UVLO VOUT VOUT EN EN PWM PWM Power On Mode3 Power Off Mode3 Figure 1. Power On/Off Sequence Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8576A Inductor Selection Input Capacitor 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) : Low ESR ceramic capacitors are recommended for input capacitor applications. Low ESR will effectively reduce the input voltage ripple caused by switching operation. Two to four 10μF/50V is sufficient for most applications. Nevertheless, this value can be decreased for lower output current requirement. Another consideration is the voltage rating of the input capacitor must be greater than the maximum input voltage. 2 L= D × (1 − D ) × VOUT 2 × fSW × 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, fSW is the switching 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 × IIOUT VIN × D × T + η × VIN 2×L 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. Output Capacitor Selection Output ripple voltage is an important index for estimating the performance. This portion consists of two parts, one is the ESR voltage of output capacitor, another part is formed by charging and discharging process of output capacitor. Refer to Figure 2, evaluate ΔVOUT1 by ideal energy equalization. According to the definition of Q, the Q value can be calculated as the following equation : ⎡ ⎤ Q = 1 × ⎢⎛⎜ IIN + 1 ΔIL − IOUT ⎞⎟ + ⎛⎜ IIN − 1 ΔIL − IOUT ⎞⎟ ⎥ 2 ⎣⎝ 2 2 ⎠ ⎝ ⎠⎦ V × IN × 1 = COUT × ΔVOUT1 VOUT fOSC where fOSC is the switching frequency, and ΔIL is the inductor ripple current. Move COUT to the left side to estimate the value of ΔVOUT1 as the following equation : ΔVOUT1 = D × IOUT η × COUT × fOSC Then, take the ESR into consideration, the ESR voltage can be determined as the following equation : I V × D × TOSC ⎞ ΔVESR = ⎛⎜ OUT + IN ⎟ × RESR 2L ⎝ 1− D ⎠ Finally, the total output ripple ΔVOUT is combined from the ΔVOUT1 and ΔVESR. In the general application, the output capacitor is recommended to use a 47μF/63V electrolytic capacitor. Power MOSFET Selection For the applications of operating at high output voltage, switching losses dominate the overall power loss. Therefore, the selection of N-MOSFET power switch must consider the parameters : Drain to Source voltage rating, RDS(ON), and low gate charge. The RT8576A provides a 5V LDR voltage for N-MOSFET switch gate driver. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be ΔIL PD(MAX) = (125°C − 25°C) / (29.5°C/W) = 3.39W for TSSOP-16 (Exposed Pad) package Inductor Current PD(MAX) = (125°C − 25°C) / (108.6°C/W) = 0.92W for SOP-16 package Output Current Time (1-D)TS Output Ripple Voltage (ac) Time ΔVOUT1 Figure 2. The Output Ripple Voltage without the Contribution of ESR 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. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For SOP-16 (Exposed Pad) package, the thermal resistance, θJA, is 29.5°C/W on a standard JEDEC 51-7 four-layer thermal test board. For SOP-16 package, the thermal resistance, θJA, is 108.6°C/W on a standard JEDEC 51-7 four-layer thermal test board. For SOP-16 (Exposed Pad) package, the thermal resistance, θJA, is 29.5°C/W on a standard JEDEC 51-7 four-layer thermal test board. For DIP-16 package, the thermal resistance, θJA, is 59.6°C/ Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 PD(MAX) = (125°C − 25°C) / (29.5°C/W) = 3.38W for SOP-16 (Exposed Pad) package PD(MAX) = (125°C − 25°C) / (59.6°C/W) = 1.68W for DIP-16 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 3 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Maximum Power Dissipation (W)1 Input Current calculated by the following formulas : Four-Layer PCB 3.5 TSSOP-16 (Exposed Pad) SOP-16 (Exposed Pad) 3.0 2.5 2.0 DIP-16 1.5 SOP-16 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 3. Derating Curve of Maximum Power Dissipation is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8576A 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 RT8576A. ` ` 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, RSSTCMP and CSSTCMP, as close as possible to pin 11. ISEN4 ISET OVP RT ENA ISW LDR VREF RISET RRT CREF The compensation circuit should be kept away from the power loops and should be shielded with a ground trace to prevent any noise coupling. ISEN3 GND ISEN2 ISEN1 PWM RSSTCMP SSTCMP CSSTCMP STATUS 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 VIN R1 L1 RLDR CIN COUT RF1 CF VIN Msw D1 RSENSE CVIN Locate the CVIN VIN as close to VIN as possible. VOUT GND Place the power components as close as possible. The traces should be wide and short especially for the highcurrent loop. Figure 4. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Outline Dimension D L U EXPOSED THERMAL PAD (Bottom of Package) E V E1 e A2 A A1 b Symbol Dimensions In Millimeters 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 4.900 5.100 0.193 0.201 e 0.65 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 2.000 3.000 0.079 0.118 V 2.000 3.000 0.079 0.118 16-Lead TSSOP (Exposed Pad) Plastic Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8576A H A M B J F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 9.804 10.008 0.386 0.394 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 16–Lead SOP Plastic Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS8576A-01 March 2013 RT8576A Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 9.804 10.008 0.386 0.394 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.270 0.050 A1 3.658 4.572 0.144 0.180 B1 1.930 2.413 0.076 0.095 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 16-Lead SOP (Exposed Pad) Plastic Package Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8576A-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT8576A Dimensions In Millimeters Symbol Dimensions In Inches Min Max Min Max A 3.700 4.320 0.146 0.170 A1 0.381 0.710 0.015 0.028 A2 3.200 3.600 0.126 0.142 b 0.360 0.560 0.014 0.022 b1 1.143 1.778 0.045 0.070 D 18.800 19.300 0.740 0.760 E 6.200 6.600 0.244 0.260 E1 7.620 8.255 0.300 0.325 e L 2.540 3.000 0.100 3.600 0.118 0.142 16-Lead DIP Plastic Package Richtek Technology Corporation 5F, No. 20, Taiyuen 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 18 DS8576A-01 March 2013