RT8462ZQW

® RT8462 High Voltage High Current LED Driver Controller for Buck, Boost or Buck-Boost Topology General Description Features The RT8462 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. With a current sense amplifier threshold of 190mV, the LED current is programmable with one external current sense resistor. With the maximum operating input voltage of 36V and output voltage up to 60V, the RT8462 is ideal for buck, boost or buck-boost operation.  With the switching frequency programmable over 100kHz to 1MHz, the external inductor and capacitors can be small while maintaining high efficiency. Dimming can be done by either analog or digital. The builtin clamping comparator and filter allow easy low noise analog dimming conversion from digital signal with only one external capacitor. The RT8462 is available in SOP-14 and WQFN-16L 3x3 packages.        High Voltage Capability : VIN Up to 36V, LED Sensing Threshold Common Mode Voltage Up to 60V Buck, Boost or Buck-Boost Operation Programmable Switching Frequency Easy Dimming Control : Analog or Digital Converting to Analog with One External Capacitor Programmable Soft-Start to Avoid Inrush Current Programmable Over Voltage Protection VIN Under Voltage Lockout and Thermal Shutdown RoHS Compliant and Halogen Free Applications     General Industrial High Power LED Lighting Desk Lights and Room Lighting Building and Street Lighting Industrial Display Backlight Pin Configuration (TOP VIEW) Ordering Information RT8462 Package Type S : SOP-14 QW : WQFN-16L 3x3 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Z : ECO (Ecological Element with Halogen Free and Pb free) RSET ISW ISP ISN VC ACTL DCTL  RoHS compliant and compatible with the current requireSuitable for use in SnPb or Pb-free soldering processes. 3 12 4 11 5 10 6 9 7 8 NC NC GATE GBIAS Richtek products are : ments of IPC/JEDEC J-STD-020. 13 SOP-14 Note :  GATE GBIAS GND VCC OVP EN SS 14 2 16 15 14 13 RSET ISW ISP ISN 1 12 2 11 GND 3 10 17 4 6 7 9 8 VC ACTL DCTL SS 5 GND VCC OVP EN WQFN-16L 3x3 Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8462 Marking Information RT8462ZQW RT8462GS RT8462GS : Product Number RT8462 GSYMDNN 82 : Product Code YMDNN : Date Code 82 YM DNN YMDNN : Date Code Typical Application Circuit L1 22µH VIN 6V to 36V CIN 10µF RT8462 VCC 9 EN 5V Analog Dimming 5 VC 8 SS 13 GBIAS RVC 10k CVC 3.3nF CSS 0.1µF LEDs RSW 0.05 ISW 2 3 ISP 4 ISN 10 OVP 1 RSET 6 ACTL 7 DCTL VOUT 60V (Max.) COUT 1µF M1 GATE 14 11 RSENSE 0.47 D1 R1 VOUT R2 GND 12 RRSET 30k CB 1µF Figure 1. Analog Dimming in Boost Configuration D1 COUT 1µF VIN2 60V (Max.) CIN2 VIN1 6V to 36V C IN1 10µF RSENSE 0.47 RT8462 11 9 EN 5V Analog Dimming 6 ACTL 7 DCTL RVC 10k CVC 3.3nF VCC CSS 0.1µF 5 VC 8 SS 13 GBIAS CB 1µF LEDs L1 22µH ISP 3 ISN 4 GATE M1 14 RSW 0.05 ISW 2 1 RSET OVP 10 GND 12 RRSET Figure 2. Analog Dimming in Buck Configuration Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 VIN2 60V (max) VIN1 6V to 36V CIN1 10µF RT8462 11 GATE VCC 9 EN 5V Analog Dimming 6 ACTL 7 DCTL 5 RVC 10k CVC 3.3nF CSS 0.1µF CIN2 VC 8 SS 13 GBIAS 14 ISW 2 4 ISN 3 ISP 10 OVP 1 RSET L1 22µH D1 VOUT COUT 1µF M1 RSW 0.05 LEDs RSENSE 0.47 R1 RRSET VOUT R2 GND 12 CB 1µF Figure 3. Analog Dimming in Buck-Boost Configuration Functional Pin Description Pin No. Pin Name Pin Function SOP-14 WQFN-16L 3x3 1 1 RSET Switch frequency set pin. Connect a resistor from RSET to GND. RRSET = 30k will set fSW = 370kHz. 2 2 ISW External MOSFET switch current sense. Connect the current sense resistor between external N-MOSFET switch and the ground. 3 3 ISP LED Current sense amplifier positive input with common mode up to 60V. 4 4 ISN LED current sense amplifier negative input. Voltage threshold between ISP and ISN is 190mV with common mode voltage up to 60V. 5 5 VC PWM Control loop compensation. 6 6 ACTL Analog dimming control. The effective programming voltage range of the pin is between 0.2V and 1.2V. 7 7 DCTL By adding a 0.47F filtering capacitor on ACTL pin, the PWM dimming signal on DCTL pin can be averaged and converted into analog dimming signal on the ACTL pin. 8 8 SS Soft-start. a capacitor of at least 10nF is required for proper soft-start. 9 9 EN 10 10 OVP 11 11 VCC 12 13 14 -- 12, GND 17 (Exposed Pad) 13 GBIAS 14 GATE 15, 16 NC Chip enable (Active High). When this pin voltage is low, the chip is in shutdown mode. Over voltage protection. The PWM converter turns off when the voltage of the pin goes to higher than 1.18V. Power supply pin of the chip. For good bypass, a low ESR capacitor is required. Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND for Maximum Power Dissipation. Internal gate driver bias. A good bypass capacitor is required. External MOSFET switch gate driver output. No internal connection. Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8462 Functional Block Diagram VOC 8.5V EN RSET VCC + 1.4V + - Shutdown - GBIAS OSC S - 5V (typ.) GATE Q + R OVP 1.18V + R - R + - - 110mV + VC ISW ISN GM + 6µA ISP SS 1.2V DCTL 1.2V + + - - GND ACTL VISP – VISN (mV) V 190 0 0.2 1.2 VACTL (V) Figure 4 Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 Absolute Maximum Ratings             (Note 1) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------GBIAS, GATE -------------------------------------------------------------------------------------------------------ISW --------------------------------------------------------------------------------------------------------------------ISP, ISN ---------------------------------------------------------------------------------------------------------------DCTL, ACTL, OVP -------------------------------------------------------------------------------------------------EN ----------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-14 ---------------------------------------------------------------------------------------------------------------WQFN-16L 3x3 -----------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 3) SOP-14, θJA ----------------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJA ------------------------------------------------------------------------------------------------WQFN-16L 3x3, θJC -----------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 4) HBM (Human Body Model) ---------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------- Recommended Operating Conditions   −0.3 to 38V −0.3 to 10V −0.3 to 1V −0.3 to 66V −0.3 to 8V (Note 2) −0.3 to 20V 1.0W 1.471W 100°C/W 68°C/W 7.5°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 5) Supply Input Voltage Range, VCC ------------------------------------------------------------------------------- 6V to 36V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VCC = 24V, No Load on any Output, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Overall Supply Current IVCC VVC  0.4V (Switching off) -- 6 7.2 mA Shutdown Current ISHDN VEN  0.7V -- 12 -- A Logic-High VIH 2 -- -- Logic-Low -- -- 0.5 -- -- 1.2 182 190 198 -- 188 -- -- 140 -- A EN Threshold Voltage VIL VEN  3V EN Input Current V A Current Sense Amplifier ISP Input Current IISP VACTL  1.25V, 12V  common mode  60V (Note 7) 1.25V  VACTL  1.2V, 12V  common mode  60V 6V  VISP  60V ISN Input Current IISN 6V  VISN  60V -- 60 -- A VC Output Current VC Threshold for PWM Switch Off IVC 0.5V  VC  2.4V -- 20 -- A -- 0.7 -- V Input Threshold (VISP  VISN) Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 mV is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8462 Parameter Symbol Test Conditions Min Typ Max Unit VACTL = 1.2V -- 1 -- VACTL = 0.2V -- 10 -- VACTL_On -- 1.3 -- V VACTL_Off -- 0.3 -- V -- 0.5 A LED Dimming Analog Dimming ACTL Pin Input Current LED Current OnThreshold at ACTL LED Current Off Threshold at ACTL DCTL Input Current DCTL Threshold Voltage IACTL A IDCTL 0.3V  VDCTL  5V -- VDCTL_H (Note 6) 2 VDCTL_L (Note 6) f SW RRSET = 30k 280 370 450 kHz RRSET = 30k -- 250 -- ns IGBIAS = 20mA 7.8 8.5 9.2 V IGATE = 50mA 6 7.2 7.8 IGATE = 100A 7.5 7.8 7.9 IGATE = 10mA -- 0.5 1 IGATE= 100A -- 0.1 0.9 1nF Load at GATE -- 20 100 ns 80 110 145 mV -- 1.18 -- V 0.3 V PWM Control Switching Frequency Minimum Off-Time Switch Gate Driver GBIAS Voltage VGBIAS GATE Voltage High VGATE_H GATE Voltage Low VGATE_L GATE Drive Rise and Fall Time PWM Switch Current Limit ISW_LIM Threshold OVP and Soft-Start V V OVP Threshold VOVP_th OVP Input Current IOVP 0.7V  VOVP  1.5V -- -- 0.1 A Soft-Start Pin Current ISS VSS  2V -- 6 -- A Thermal Shutdown Protection TSD -- 145 -- Thermal Shutdown Hysteresis TSD -- 10 -- C Note 1. Stresses beyond those listed under “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. If connected with a 20kΩ serial resistor, ACTL and DCTL can go up to 36V. Note 3. For WQFN-16L 3x3, θJA is measured in natural convection at TA = 25°C on a high-effective thermal conductivity test board of JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the package. For SOP-14, θJA is measured in natural convection at TA = 25°C on a low-effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 4. Devices are ESD sensitive. Handling precaution is recommended. Note 5. The device is not guaranteed to function outside its operating conditions. Note 6. Guaranteed by design, not subjected to production test. Note 7. The ACTL dimming curve is saturating when VACTL ≥ 1.2V. Please refer to typical operation characteristics curve of ILED vs. VACTL. This item is not subjected to production test. Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 Typical Operating Characteristics Efficiency vs. Input Voltage Efficiency vs. Input Voltage 100 Boost 95 95 90 90 Efficiency (%) Efficiency (%) 100 85 80 75 Buck − Boost 85 80 75 VOUT = 40V, IOUT = 410mA, L = 22μH 70 VOUT = 20V, IOUT = 410mA, L = 22μH 70 12 15 18 21 24 27 30 12 15 Efficiency vs. Input Voltage 100 24 27 30 Switching Frequency vs. Input Voltage Buck Switching Frequency (kHz)1 Efficiency (%) 21 400 95 90 85 80 75 380 360 340 320 VOUT = 10V, IOUT = 410mA, L = 22μH 70 300 12 15 18 21 24 27 30 6 11 Supply Current vs. Input Voltage 9 18 Shutdown Current (μA)1 20 8 7 6 5 4 3 2 6 11 16 21 26 31 Input Voltage (V) Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 26 31 36 16 14 12 10 8 6 4 2 VIN = 6V to 36V 0 21 Shutdown Current vs. Input Voltage 10 1 16 Input Voltage (V) Input Voltage (V) Supply Current (mA) 18 Input Voltage (V) Input Voltage (V) VIN = 6V to 36V, VEN = 0V 0 36 6 11 16 21 26 31 36 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8462 VISP – VISN Threshold vs. Temperature VISP – VISN Threshold vs. Input Voltage 200 VISP – VISN Threshold (mV) VISP – VISN Threshold (mV) 200 195 190 185 195 190 185 180 180 6 11 16 21 26 31 -50 36 -25 Input Voltage (V) 50 75 100 125 LED Current vs. ACTL Voltage ACTL Off Threshold vs. Input Voltage 450 0.27 400 0.26 LED Current (mA) ACTL Off Threshold (V) 25 Temperature (°C) 0.28 0.25 0.24 0.23 0.22 350 300 250 200 150 100 0.21 50 0 0.20 6 11 16 21 26 31 0.2 36 0.4 Input Voltage (V) 400 140 350 130 ISW Threshold (mV) 150 300 250 200 150 100 f = 10kHz 0 0.8 1 1.2 1.4 ISW Threshold vs. Input Voltage 450 50 0.6 ACTL Voltage (V) LED Current vs. DCTL PWM Duty LED Current (mA) 0 120 110 100 90 80 70 60 50 0 20 40 60 80 DCTL PWM Duty (%) Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 100 6 11 16 21 26 31 36 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 OVP vs. Input Voltage GATE Voltage vs. Input Voltage 1.20 8 1.19 OVP_H 1.18 OVP (V) GATE Voltage (V) GATE_Hi 1.17 OVP_L 1.16 6 4 2 1.15 No Load GATE_Lo 1.14 0 6 11 16 21 26 31 36 6 16 21 26 Input Voltage (V) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (20V/Div) VOUT (20V/Div) GATE (10V/Div) GATE (10V/Div) IOUT (500mA/Div) IOUT (500mA/Div) Time (2.5ms/Div) Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 11 Input Voltage (V) 31 36 Time (100μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8462 Applications Information The RT8462 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. The LED current can be programmed by an external resistor. The input voltage range of the RT8462 can be up to 36V and the output voltage can be up to 60V. The RT8462 provides analog and PWM dimming to achieve LED current control. GBIAS Regulator and Bypass Capacitor The GBIAS pin requires a capacitor for stable operation and to store the charge for the large GATE switching currents. Choose a 25V rated low ESR, X7R or X5R ceramic capacitor for best performance. The value of a 1μF capacitor will be adequate for many applications. Place the capacitor close to the IC to minimize the trace length to the GBIAS pin and also to the IC ground. An internal current limit on the GBIAS output protects the RT8462 from excessive on-chip power dissipation. The GBIAS pin has its own under voltage disable (UVLO) set to 4.3V(typical) to protect the external FETs from excessive power dissipation caused by not being fully enhanced. If the input voltage, VIN, will not exceed 8V, then the GBIAS pin should be connected to the input supply. Be aware if GBIAS supply is used to drive extra circuits besides RT8462, typically the extra GBIAS load should be limited to less than 10mA. Loop Compensation The RT8462 uses an internal error amplifier whose compensation pin (VC) allowing the loop response optimized for specific application. The external inductor, output capacitor and the compensation resistor and capacitor determine the loop stability. The inductor and output capacitor are chosen based on performance, size and cost. The compensation resistor and capacitor at VC are selected to optimize control loop response and stability. For typical LED applications, a 3.3nF compensation capacitor at VC is adequate, and a series resistor should always be used to increase the slew rate on the VC pin to maintain tighter regulation of LED current during fast transients on the input supply to the converter an external resistor in series with a capacitor is connected Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 from the VC pin to GND to provide a pole and a zero for proper loop compensation. The typical compensation for the RT8462 is 10kΩ and 3.3nF. Soft-Start The soft-start of the RT8462 can be achieved by connecting a capacitor from SS pin to GND. The built-in soft-start circuit reduces the start-up current spike and output voltage overshoot. The soft-start time is determined by the external capacitor charged by an internal 6μA constant charging current. The SS pin directly limits the rate of voltage rise on the VC pin, which in turn limits the peak switch current. The soft-start interval is set by the soft-start capacitor selection according to the equation : 2.4V tSS  CSS  6μA A typical value for the soft-start capacitor is 0.1μF. The soft-start capacitor is discharged when EN/UVLO falls below its threshold, during an over temperature event or during an GBIAS under voltage event. LED Current Setting The LED current is programmed by placing an appropriate value current sense resistor between the ISP and ISN pins. Typically, sensing of the current should be done at the top of the LED string. The ACTL pin should be tied to a voltage higher than 1.2V to get the full-scale 190mV (typical) threshold across the sense resistor. The ACTL pin can also be used to dim the LED current to zero, although relative accuracy decreases with the decreasing voltage sense threshold. When the ACTL pin voltage is less than 1.2V, the LED current is : (VACTL  0.2)  0.19 ILED  RSENSE Where, RSENSE is the resistor between ISP and ISN. When the voltage of ACTL is higher than 1.2V, the LED current is regulated to : ILED(MAX)  190mV RSENSE is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 The amplitude of this signal is increased by high LED load current, low switching frequency and/or a smaller value output filter capacitor. The compensation capacitor on the VC pin filters the signal so the average difference between ISP and ISN is regulated on the user-programmed value. Frequency vs. RRSET 1000 900 800 Frequency (kHz)1 The ACTL pin can also be used in conjunction with a thermistor to provide over temperature protection for the LED load, or with a voltage divider to VIN to reduce output power and switching current when VIN is low. The presence of a time varying differential voltage signal (ripple) across ISP and ISN at the switching frequency is expected. 700 600 500 400 300 200 100 0 0 Programmable Switching Frequency The RSET frequency adjust pin allows the user to program the switching frequency from 100kHz to 1MHz for optimized efficiency and performance or external component size. Higher frequency operation allows for smaller component size but increases switching losses and gate driving current, and may not allow sufficiently high or low duty cycle operation. Lower frequency operation gives better performance but with larger external component size. For an appropriate RRSET resistor value see Table 1 or Figure 5. An external resistor from the RSET pin to GND is required-do not leave this pin open. Table 1. Switching Frequency vs. RRSET Value (1% Resistors) 15 30 45 60 75 90 105 120 135 R RRSET (kΩ) RSET (kΩ) Figure 5. Switching Frequency vs. RRSET Output Over Voltage Setting The RT8462 is equipped with Over Voltage Protection (OVP) function. When the voltage at OVP pin exceeds a threshold of approximately 1.18V, the power switch is turned off. The power switch can be turned on again once the voltage at OVP pin drops below 1.18V. For the Boost and Buck-Boost application, the output voltage could be clamped at a certain voltage level. The OVP voltage can be set by the following equation : R1   VOUT, OVP  1.18   1   R2   Where, fOSC (kHZ) RRSET (k) 1000 8.34 800 11.41 600 16.68 500 20.9 Over Temperature Protection 300 38.04 200 60.35 100 130 The RT8462 has Over Temperature Protection (OTP) function to prevent the excessive power dissipation from overheating. The OTP function will shut down switching operation when the die junction temperature exceeds 145°C. The chip will automatically start to switch again when the die junction temperature cools off. Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 R1 and R2 are the voltage divider from VOUT to GND with the divider center node connected to OVP pin. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8462 Inductor Selection The converter operates in discontinuous conduction mode when the inductance value is less than the value LBCM. With an inductance greater than LBCM, the converter operates in Continuous Conduction Mode (CCM). The inductance LBCM is determined by the following equations. For Buck application : LBCM  VOUT  VIN  VOUT    2  IOUT  f  VIN  For Boost application :  VOUT  VIN  VIN2 LBCM     2  IOUT  f  VOUT 2  For Buck-Boost application : VIN2 VOUT LBCM   2  IOUT  f  VIN  VOUT 2 where For Buck-Boost application : VIN2 VOUT L=  2  0.3  IOUT  f  VIN  VOUT 2 The inductor must also be selected with a saturation current rating greater than the maximum inductor current during normal operation. The maximum inductor current can be calculated by the following equations. For Buck application : VOUT  VIN  VOUT    2  L  f  VIN  For Boost application : IPEAK = IOUT + VOUT VOUT  VIN  VIN   IOUT +   VIN   2 f L  VOUT  For Buck-Boost application : 2 IPEAK = IPEAK = VOUT  VIN   VOUT  VIN   IOUT +  VIN   2  f  L  VIN  VOUT  VOUT = output voltage. where VIN = input voltage. η is the efficiency of the power converter. f = operating frequency. IOUT = LED current. Choose an inductance based on the operating frequency, input voltage and output voltage to provide a current mode ramp signal during the MOSFET on period for PWM control loop regulation. The inductance also determines the inductor ripple current. Operating the converter in CCM is recommended, which will have the smaller inductor ripple current and hence the less conduction losses from all converter components. As a design example, to design the peak to peak inductor ripple to be ±30% of the output current, the following equations can be used to estimate the size of the needed inductance : For Buck application : L= VOUT  VIN  VOUT    2  0.3  IOUT  f  VIN  For Boost application : L=  VOUT  VIN  VIN2    2  0.3  IOUT  f  VOUT 2  Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 Power MOSFET Selection For applications operating at high input or output voltages, the power N-MOS FET switch is typically chosen for drain voltage VDS rating and low gate charge. Consideration of switch on-resistance, R DS(ON), is usually secondary because switching losses dominate power loss. The GBIAS regulator on the RT8462 has a fixed current limit to protect the IC from excessive power dissipation at high VIN, so the N-MOSFET should be chosen so that the product of Qg at 5V and switching frequency does not exceed the GBIAS current limit. Moreover, to obtain better conversion efficiency, GATE high level must be higher than the gate threshold voltage Vgs(th) of the power N-MOSFET. If GATE high level is lower, an external totem pole circuit has to be added. ISW Sense Resistor Selection The resistor, RSW, between the Source of the external NMOSFET and GND should be selected to provide adequate switch current to drive the application without exceeding the current limit threshold set by the ISW pin sense threshold of RT8462. The ISW sense resistor value can be calculated according to the formula below : is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 2 RT8462 RSW  Current Limlit Threshold Minimum Value IOCP where IOCP is about 1.33 to 1.5 times of inductor peak current IPEAK. The placement of RSW should be close to the source of the N-MOSFET and the IC GND of the RT8462. The ISW pin input to RT8462 should be a Kelvin sense connection to the positive terminal of RSW. Schottky Diode Selection The Schottky diode, with their low forward voltage drop and fast switching speed, is necessary for the RT8462 applications. In addition, power dissipation, reverse voltage rating and pulsating peak current are the important parameters for the Schottky diode selection. Choose a suitable Schottky diode whose reverse voltage rating is greater than maximum output voltage. The diode’s average current rating must exceed the average output current. The diode conducts current only when the power switch is turned off (typically less than 50% duty cycle). If using the PWM feature for dimming, it is important to consider diode leakage, which increases with the temperature, from the output during the PWM low interval. Therefore, choose the Schottky diode with sufficiently low leakage current. Capacitor Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. For most the RT8462 applications, a 10μF ceramic capacitor is sufficient. A value higher or lower may be used depending on the noise level from the input supply and the input current to the converter. In Boost application, the output capacitor is typically a ceramic capacitor and is selected based on the output voltage ripple requirements. The minimum value of the output capacitor COUT is approximately given by the following equation : COUT  For LED applications, the equivalent resistance of the LED is typically low and the output filter capacitor should be sized to attenuate the current ripple. Use of X7R type ceramic capacitors is recommended. Lower operating frequencies will require proportionately higher capacitor values. 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 WQFN-16L 3x3 packages, the thermal resistance, θJA, is 68°C/W on a standard JEDEC 51-7 four-layer thermal test board. For SOP-14 packages, the thermal resistance, θJA, is 100°C/W on a standard JEDEC 51-3 single-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (68°C/W) = 1.471W for WQFN-16L 3x3 package P D(MAX) = (125°C − 25°C) / (100°C/W) = 1.0W for SOP-14 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curves in Figure 6 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. IOUT  VOUT VIN  VRIPPLE  fSW Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8462 Layout Consideration Maximum Power Dissipation (W)1 1.60 1.40 PCB layout is very important to design power switching converter circuits. The layout guidelines are suggested as follows : WQFN-16L 3x3 (Four-Layer PCB) 1.20 1.00  The power components L1, D1, CIN, M1 and COUT must be placed as close to each other as possible to reduce the ac current loop area. The PCB trace between power components must be as short and wide as possible due to large current flow through these traces during operation. 125  The input capacitor CVCC must be placed as close to VCC pin as possible. Figure 6. Derating Curve of Maximum Power Dissipation  Place the compensation components to VC pin as close as possible to avoid noise pick up.  Connect GND pin and Exposed Pad to a large ground plane for maximum power dissipation and noise reduction. 0.80 0.60 SOP-14 (Single-Layer PCB) 0.40 0.20 0.00 0 25 50 75 100 Ambient Temperature (°C) Place these components as close as possible D1 L1 VIN M1 COUT GND RSW GND RSENSE RSET ISW ISP ISN VC ACTL DCTL 14 2 13 3 12 4 11 5 10 6 9 7 8 GATE GBIAS GND VCC OVP EN SS CIN CVCC RVC CSS CVC GND Figure 7. PCB Layout Guide Copyright © 2019 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8462-09 April 2019 RT8462 Outline Dimension H A M J B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 8.534 8.738 0.336 0.344 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 14–Lead SOP Plastic Package Copyright © 2019 Richtek Technology Corporation. All rights reserved. DS8462-09 April 2019 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8462 D SEE DETAIL A D2 L 1 E E2 e b A A1 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 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 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 1.300 1.750 0.051 0.069 E 2.950 3.050 0.116 0.120 E2 1.300 1.750 0.051 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 16L QFN 3x3 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 16 DS8462-09 April 2019