® RT6242A/B 12A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter General Description Features The RT6242A/B is a synchronous step-down converter with Advanced Constant On-Time (ACOTTM) mode control. 4.5V to 18V Input Voltage Range 12A Output Current Ω 12mΩ Ω Internal High-Side N-MOSFET and 5.4mΩ Internal Low-Side N-MOSFET Advanced Constant On-Time Control Fast Transient Response Support All Ceramic Capacitors Up to 95% Efficiency Adjustable Switching Frequency from 300kHz to 700kHz Adjustable Output Voltage from 0.7V to 8V Adjustable Soft-Start Pre-bias Start-Up Adjustable Current Limit from 6A to 16A Cycle-by-Cycle Over Current Protection Power Good Output Input Under-Voltage Lockout Hiccup Mode Under-Voltage Protection Thermal Shutdown Protection TM The ACOT provides a very fast transient response with few external components. The low impedance internal MOSFET supports high efficiency operation with wide input voltage range from 4.5V to 18V. The proprietary circuit of the RT6242A/B enables to support all ceramic capacitors. The output voltage can be adjustable between 0.7V and 8V. The soft-start is adjustable by an external capacitor. Ordering Information RT6242A/B Package Type QUF : UQFN-16JL 3x3 (U-Type) (FC) Lead Plating System G : Green (Halogen Free and Pb Free) UVP Option H : Hiccup Mode UVP L : Latched OVP & UVP A : PSM B : PWM Applications Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Note : Suitable for use in SnPb or Pb-free soldering processes. Industrial and Commercial Low Power Systems Computer Peripherals LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs Simplified Application Circuit VIN RT6242A/B SW VIN VOUT BOOT EN Signal Power Good EN Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 FB RT PGOOD RLIM PVCC SS GND is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6242A/B Pin Configurations Marking Information RT6242AHGQUF RLIM EN SW SW (TOP VIEW) 16 15 14 13 7D= : Product Code SW PVCC 3 10 SW RT 4 9 BOOT 5 6 7 8 PGOOD SW 11 GND 12 2 SS 1 FB VIN AGND UQFN-16JL 3x3 (FC) 7D=YM DNN YMDNN : Date Code RT6242ALGQUF 7C= : Product Code 7C=YM DNN YMDNN : Date Code RT6242BHGQUF 78= : Product Code 78=YM DNN YMDNN : Date Code RT6242BLGQUF 75= : Product Code 75=YM DNN YMDNN : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 AGND Analog Ground. 2 FB Feedback Voltage Input. It is used to regulate the output of the converter to a set value via an external resistive voltage divider. The feedback reference voltage is 0.7V typically. 3 PVCC Internal Regulator Output. Connect a 1F capacitor to GND to stabilize output voltage. 4 RT An External Timing Resistor Adjusts the Switching Frequency of the Device. 5 SS Soft-Start Time Setting. An external capacitor should be connected between this pin and GND. 6 VIN Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a suitably large (10F x 2) ceramic capacitor. 7 GND Ground. 8 PGOOD Power Good Indicator Open-Drain Output. 9 BOOT Bootstrap. This capacitor is needed to drive the power switch's gate above the supply voltage. It is connected between SW and BOOT pins to form a floating supply across the power switch driver. A 0.1F capacitor is recommended for use. 10 to 14 SW Switch Node. Connect this pin to an external L-C filter. 15 EN 16 RLIM Enable Control Input. A logic-high enables the converter; a logic-low forces the IC into shutdown mode reducing the supply current to less than 10A. An External Resistor Adjusts the Current Limit of the Device. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Function Block Diagram BOOT PVCC EN POR & Reg VBIAS Min. Off-Time PVCC VIN VREF OC UGATE Control Driver SW LGATE UV & OV PVCC 6µA SS GND Ripple Gen. FB VIN + + Comparator ZC 0.9 VREF FB Comparator + PGOOD - On-Time Operation The RT6242A/B is a synchronous step-down converter with advanced Constant On-Time control mode. Using the ACOTTM control mode can reduce the output capacitance and fast transient response. It can minimize the component size without additional external compensation network. Current Protection The inductor current is monitored via the internal switches cycle-by-cycle. Once the output voltage drops under UV threshold, the RT6242A/B will enter hiccup mode. UVLO Protection Power Good After soft-start has finished, the power good function will be activated. The PGOOD pin is an open-drain output. If the FB voltage is lower than 85% VREF, the PGOOD pin will be pulled low. To protect the chip from operating at insufficient supply voltage, the UVLO is needed. When the input voltage of VIN is lower than the UVLO falling threshold voltage, the device will be lockout. Thermal Shutdown PVCC The regulator provides 5V power to supply the internal control circuit. 1μF ceramic capacitor for decoupling and stability is required. Soft-Start When the junction temperature exceeds the OTP threshold value, the IC will shut down the switching operation. Once the junction temperature cools down and is lower than the OTP lower threshold, the converter will autocratically resume switching. In order to prevent the converter output voltage from overshooting during the startup period, the soft-start function is necessary. The soft-start time is adjustable by an external capacitor. Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6242A/B Absolute Maximum Ratings (Note 1) Supply Voltage, VIN -----------------------------------------------------------------------------------------------Switch Voltage, SW -----------------------------------------------------------------------------------------------BOOT to SW --------------------------------------------------------------------------------------------------------EN to GND ------------------------------------------------------------------------------------------------------------Other Pins Voltage -------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C UQFN-16JL 3x3 (FC) ----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) UQFN-16JL 3x3 (FC), θJA -----------------------------------------------------------------------------------------UQFN-16JL 3x3 (FC), θJC ----------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ---------------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 20V −0.3V to (VIN + 0.3V) −0.3V to 6V −0.3V to 6V −0.3V to 6V 3.623W 27.6°C/W 5.6°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Voltage, VIN ------------------------------------------------------------------------------------------------ 4.5V to 18V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Current Shutdown Current ISHDN VEN = 0V -- 1.5 10 A Quiescent Current IQ VEN = 2V, VFB = 1V -- 0.8 1.2 mA Logic-High 1.1 1.2 1.3 Hysteresis -- 0.2 -- Logic Threshold EN Voltage V VREF Voltage Feedback Threshold Voltage VREF 4.5V VIN 18V 0.693 0.7 0.707 V Feedback Input Current IFB VFB = 0.71V 0.1 -- 0.1 A VPVCC 6V VIN 18V, 0 < IPVCC 5mA -- 5 -- V Line Regulation 6V VIN 18V, IPVCC = 5mA -- -- 20 mV Load Regulation 0 IPVCC 5mA -- -- 100 mV VIN = 6V, VPVCC = 4V -- 150 -- mA PVCC Output PVCC Output Voltage Output Current IPVCC RDS(ON) Switch On-Resistance High-Side RDS(ON)_H -- 12 -- Low-Side RDS(ON)_L -- 5.4 -- Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 m is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Parameter Symbol Test Conditions Min Typ Max Unit 13 16 -- A -- 150 -- C -- 200 -- ns Current Limit Current Limit ILIM RLIM = 66k Thermal Shutdown Thermal Shutdown Threshold TSD On-Time Timer Control VIN = 12V, VOUT = 1.05V, RRT = 150k On-Time tON Minimum On-Time tON(MIN) -- 60 -- ns Minimum Off-Time tOFF(MIN) -- 230 -- ns VSS = 0V 5 6 7 A Wake Up VIN 4 4.2 4.4 -- 0.5 -- FB Rising 85 90 95 FB Falling -- 80 -- PGOOD = 0.1V 10 20 -- mA 115 120 125 % OVP Propogation Delay -- 10 -- s UVP Threshold 55 60 65 % UVP Hysteresis -- 17 -- % UVP Propogation Delay -- 250 -- s RRT = 106k 600 700 800 RRT = 150k 430 500 570 RRT = 250k 250 300 350 Soft-Start SS Charge Current UVLO UVLO Threshold Hysteresis V Power Good PGOOD Threshold PGOOD Sink Current % OVP and UVP Protection OVP Threshold Switching Frequency f SW kHz 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. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6242A/B Typical Application Circuit VIN C1 10µF x 2 C2 0.1µF BOOT 8 PGOOD 15 Enable 5 C5 10nF C6 0.1µF 9 EN FB 2 SS PVCC 3 16 RLIM RLIM L1 1µH RT6242A/B 10 to 14 6 VIN SW C4 1µF VOUT 1.4V/12A R1 20k C3 C7 22µF x 3 R2 20k VPVCC RT 4 AGND 1 GND 7 RT RLIM = 172k, OCP typical 6A RLIM = 94k, OCP typical 11.4A RLIM = 80k, OCP typical 13.3A RLIM = 66k, OCP typical 16A Table 1. Suggested Component Values VOUT (V) R1 (k) R2 (k) C3 (pF) L1 (H) C7 (F) 1 8.66 20 -- 1 66 1.4 20 20 -- 1 66 1.8 31.6 20 10 1 66 2.5 51.1 20 10 1.2 66 5 124 20 22 1.5 66 Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Typical Operating Characteristics Efficiency vs. Output Current 98 94 94 90 90 VOUT VOUT VOUT VOUT VOUT VOUT VOUT 86 82 78 74 = = = = = = = Efficiency (%) Efficiency (%) Efficiency vs. Output Current 98 1V 1.1V 1.2V 1.5V 1.8V 3.3V 5V 0 2 4 82 78 74 RT6242A : PSM, VIN = 12V, fSW = 500kHz 70 VOUT VOUT VOUT VOUT VOUT VOUT VOUT 86 6 8 10 0 2 4 Output Current (A) 94 94 86 82 = = = = = = 1V 1.1V 1.2V 1.5V 1.8V 3.3V 78 74 10 12 90 VOUT VOUT VOUT VOUT VOUT VOUT 86 82 = = = = = = 1V 1.1V 1.2V 1.5V 1.8V 3.3V 78 74 RT6242A : PSM, VIN = 5V, fSW = 500kHz 70 RT6242B : PWM, VIN = 5V, fSW = 500kHz 70 0 2 4 6 8 10 12 0 2 4 Output Current (A) 8 10 12 Output Voltage vs. Input Voltage 1.30 RT6242A 1.28 6 Output Current (A) Output Voltage vs. Input Voltage 1.30 RT6242B 1.28 1.26 Output Voltage (V) 1.26 Output Voltage (V) 8 Efficiency vs. Output Current 98 Efficiency (%) Efficiency (%) Efficiency vs. Output Current VOUT VOUT VOUT VOUT VOUT VOUT 6 Output Current (A) 98 90 1V 1.1V 1.2V 1.5V 1.8V 3.3V 5V RT6242B : PWM, VIN = 12V, fSW = 500kHz 70 12 = = = = = = = 1.24 1.22 IOUT = 0A IOUT = 6A IOUT = 9A 1.20 1.18 1.16 1.14 1.24 1.22 1.20 IOUT = 0A IOUT = 6A IOUT = 9A 1.18 1.16 1.14 1.12 VOUT = 1.2V 1.10 1.12 VOUT = 1.2V 1.10 4 6 8 10 12 14 16 Input Voltage (V) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 18 4 6 8 10 12 14 16 18 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6242A/B Output Voltage vs. Output Current Output Voltage vs. Output Current 1.30 1.30 RT6242A 1.28 1.26 Output Voltage (V) 1.26 Output Voltage (V) RT6242B 1.28 1.24 1.22 VIN = 17V VIN = 12V VIN = 6V 1.20 1.18 1.16 1.24 1.22 1.20 VIN = 17V VIN = 12V VIN = 6V 1.18 1.16 1.14 1.14 1.12 1.12 VOUT = 1.2V 1.10 0 1 2 3 4 5 6 7 8 9 VOUT = 1.2V 1.10 0 10 1 2 3 5 Frequency vs. Input Voltage 7 8 9 10 Frequency vs. Temperature 700 650 650 600 600 Frequency (kHz)1 700 550 500 450 400 350 550 500 450 400 350 VIN = 12V, VOUT = 1.2V VOUT = 1.2V 300 300 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 -50 -25 Input Voltage (V) 0 25 50 75 100 125 Temperature (°C) Feedback Threshold vs. Temperature Frequency vs. RRT Resistor 0.707 0.706 0.705 700 0.704 0.703 0.702 0.701 0.700 0.699 0.698 0.697 0.696 0.695 0.694 600 650 Frequency (kHz)1 Feedback Threshold (V) 6 Output Current (A) Output Current (A) Frequency (kHz)1 4 VIN = 17V VIN = 12V VIN = 4.5V 550 500 450 400 350 VIN = 12V 300 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 125 100 115 130 145 160 175 190 205 220 235 250 RRT (k Ω) is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Load Transient Response Load Transient Response RT6242A RT6242B VOUT (50mV/Div) VOUT (50mV/Div) IOUT (5A/Div) IOUT (5A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 0.1A to 12A VIN = 12V, VOUT = 1.2V, IOUT = 0.1A to 12A Time (100μs/Div) Time (100μs/Div) Load Transient Response Load Transient Response RT6242B RT6242A VOUT (50mV/Div) VOUT (50mV/Div) IOUT (5A/Div) IOUT (5A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 6A to 12A RT6242A VIN = 12V, VOUT = 1.2V, IOUT = 6A to 12A Time (100μs/Div) Time (100μs/Div) Output Ripple Voltage Output Ripple Voltage VIN = 12V, VOUT = 1.2V, IOUT = 50mA VOUT (50mV/Div) VIN = 12V, VOUT = 1.2V, IOUT = 50mA VOUT (10mV/Div) VLX (10V/Div) VLX (10V/Div) ILX (2A/Div) ILX (5A/Div) Time (50μs/Div) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 RT6242B Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6242A/B Output Ripple Voltage Output Ripple Voltage RT6242A RT6242B VOUT (10mV/Div) VOUT (10mV/Div) VLX (10V/Div) VLX (10V/Div) ILX (5A/Div) ILX (5A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 12A Time (1μs/Div) Time (1μs/Div) Power On from EN Power Off from EN RT6242A RT6242A VEN (5V/Div) VEN (5V/Div) VOUT (1V/Div) VOUT (1V/Div) VLX (10V/Div) VIN = 12V, VOUT = 1.2V, IOUT = 0.1A VLX (10V/Div) ILX (2A/Div) ILX (2A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 0.1A Time (2ms/Div) Time (2ms/Div) Power On from EN Power Off from EN VEN (5V/Div) RT6242B VEN (5V/Div) RT6242B VOUT (1V/Div) VOUT (1V/Div) VLX (10V/Div) VIN = 12V, VOUT = 1.2V, IOUT = 12A VLX (10V/Div) VIN = 12V, VOUT = 1.2V, IOUT = 10A ILX (10A/Div) Time (4ms/Div) Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 ILX (10A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 10A Time (4ms/Div) is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B UVP Short (Latch Mode) VIN (5V/Div) VOUT (1V/Div) UVP Short (Hiccup Mode) VIN (5V/Div) VIN = 12V, VOUT = 1.2V, IOUT = Short VIN = 12V, VOUT = 1.2V, IOUT = Short VOUT (500mV/Div) VLX (10V/Div) VLX (10V/Div) ILX (10A/Div) ILX (10A/Div) Time (2ms/Div) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6242A/B Application Information Inductor Selection Selecting an inductor involves specifying its inductance and also its required peak current. The exact inductor value is generally flexible and is ultimately chosen to obtain the best mix of cost, physical size, and circuit efficiency. Lower inductor values benefit from reduced size and cost and they can improve the circuit's transient response, but they increase the inductor ripple current and output voltage ripple and reduce the efficiency due to the resulting higher peak currents. Conversely, higher inductor values increase efficiency, but the inductor will either be physically larger or have higher resistance since more turns of wire are required and transient response will be slower since more time is required to change current (up or down) in the inductor. A good compromise between size, efficiency, and transient response is to use a ripple current (ΔIL) about 15% to 40% of the desired full output load current. Calculate the approximate inductor value by selecting the input and output voltages, the switching frequency (fSW), the maximum output current (IOUT(MAX)) and estimating a ΔIL as some percentage of that current. L= VOUT VIN VOUT VIN fSW IL Once an inductor value is chosen, the ripple current (ΔIL) is calculated to determine the required peak inductor current. VOUT VIN VOUT IL = VIN fSW L I IL(PEAK) = IOUT(MAX) L 2 I IL(VALLY) = IOUT(MAX) L 2 Inductor saturation current should be chosen over IC's current limit. Input Capacitor Selection The input filter capacitors are needed to smooth out the switched current drawn from the input power source and to reduce voltage ripple on the input. The actual capacitance value is less important than the RMS current rating (and voltage rating, of course). The RMS input ripple current (IRMS) is a function of the input voltage, output voltage, and load current : Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 V IRMS = IOUT(MAX) OUT VIN VIN 1 VOUT Ceramic capacitors are most often used because of their low cost, small size, high RMS current ratings, and robust surge current capabilities. However, take care when these capacitors are used at the input of circuits supplied by a wall adapter or other supply connected through long, thin wires. Current surges through the inductive wires can induce ringing at the RT6242A/B input which could potentially cause large, damaging voltage spikes at VIN. If this phenomenon is observed, some bulk input capacitance may be required. Ceramic capacitors (to meet the RMS current requirement) can be placed in parallel with other types such as tantalum, electrolytic, or polymer (to reduce ringing and overshoot). Choose capacitors rated at higher temperatures than required. Several ceramic capacitors may be paralleled to meet the RMS current, size, and height requirements of the application. The typical operating circuit uses two 10μF and one 0.1μF low ESR ceramic capacitors on the input. Output Capacitor Selection The RT6242A/B are optimized for ceramic output capacitors and best performance will be obtained using them. The total output capacitance value is usually determined by the desired output voltage ripple level and transient response requirements for sag (undershoot on positive load steps) and soar (overshoot on negative load steps). Output Ripple Output ripple at the switching frequency is caused by the inductor current ripple and its effect on the output capacitor's ESR and stored charge. These two ripple components are called ESR ripple and capacitive ripple. Since ceramic capacitors have extremely low ESR and relatively little capacitance, both components are similar in amplitude and both should be considered if ripple is critical. is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B VRIPPLE = VRIPPLE(ESR) VRIPPLE(C) Soft-Start (SS) VRIPPLE(ESR) = IL RESR IL VRIPPLE(C) = 8 COUT fSW The RT6242A/B soft-start uses an external capacitor at SS to adjust the soft-start timing according to the following equation : Feed-forward Capacitor (Cff) t ms The RT6242A/B are optimized for ceramic output capacitors and for low duty cycle applications. However for high-output voltages, with high feedback attenuation, the circuit's response becomes over-damped and transient response can be slowed. In high-output voltage circuits (VOUT > 3.3V) transient response is improved by adding a small “feed-forward” capacitor (Cff) across the upper FB divider resistor (Figure 1), to increase the circuit's Q and reduce damping to speed up the transient response without affecting the steady-state stability of the circuit. Choose a suitable capacitor value that following below step. Get the BW the quickest method to do transient response form no load to full load. Confirm the damping frequency. The damping frequency is BW. VOUT Cff FB RT6242A/B Following below equation to get the minimum capacitance range in order to avoid UV occur. COUT VOUT 0.6 1.2 (ILIM Load Current) 0.8 T 6μA CSS VREF T Do not leave SS unconnected. Enable Operation (EN) For automatic start-up, the low-voltage EN pin must be connected to VIN with a 100kΩ resistor. EN can be externally pulled to VIN by adding a resistor-capacitor delay (REN and CEN in Figure 2). Calculate the delay time using EN's internal threshold where switching operation begins (1.2V, typical). EN VIN R2 GND Figure 1. Cff Capacitor Setting ISS μA An external MOSFET can be added to implement digital control of EN (Figure 3). In this case, a 100kΩ pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. To prevent enabling circuit when VIN is smaller than the VOUT target value or some other desired voltage level, a resistive voltage divider can be placed between the input voltage and ground and connected to EN to create an additional input under voltage lockout threshold (Figure 4). BW R1 CSS nF 0.7 REN CEN EN RT6242A/B GND Figure 2. External Timing Control Cff can be calculated base on below equation : Cff 1 2 3.1412 R1 BW 0.8 Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT6242A/B VIN REN 100k External BOOT Bootstrap Diode EN Q1 Enable RT6242A/B GND Figure 3. Digital Enable Control Circuit VIN REN1 External BOOT Capacitor Series Resistance EN REN2 RT6242A/B GND Figure 4. Resistor Divider for Lockout Threshold Setting Output Voltage Setting Set the desired output voltage using a resistive divider from the output to ground with the midpoint connected to FB. The output voltage is set according to the following equation : VOUT = 0.7 x (1 + R1 / R2) VOUT R1 FB RT6242A/B When the input voltage is lower than 5.5V it is recommended to add an external bootstrap diode between VIN (or VINR) and the BOOT pin to improve enhancement of the internal MOSFET switch and improve efficiency. The bootstrap diode can be a low cost one such as 1N4148 or BAT54. R2 GND The internal power MOSFET switch gate driver is optimized to turn the switch on fast enough for low power loss and good efficiency, but also slow enough to reduce EMI. Switch turn-on is when most EMI occurs since VSW rises rapidly. During switch turn-off, SW is discharged relatively slowly by the inductor current during the dead time between high-side and low-side switch on-times. In some cases it is desirable to reduce EMI further, at the expense of some additional power dissipation. The switch turn-on can be slowed by placing a small (<47Ω) resistance between BOOT and the external bootstrap capacitor. This will slow the high-side switch turn-on and VSW's rise. To remove the resistor from the capacitor charging path (avoiding poor enhancement due to undercharging the BOOT capacitor), use the external diode shown in Figure 6 to charge the BOOT capacitor and place the resistance between BOOT and the capacitor/diode connection. 5V Figure 5. Output Voltage Setting BOOT Place the FB resistors within 5mm of the FB pin. Choose R2 between 10kΩ and 100kΩ to minimize power consumption without excessive noise pick-up and calculate R1 as follows : R2 (VOUT 0.7) R1 0.7 For output voltage accuracy, use divider resistors with 1% or better tolerance. Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 RT6242A/B 0.1µF SW Figure 6. External Bootstrap Diode PVCC Capacitor Selection Decouple PVCC to GND with a 1μF ceramic capacitor. High grade dielectric (X7R, or X5R) ceramic capacitors are recommended for their stable temperature and bias voltage characteristics. is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Hiccup Mode The RT6242AH/RT6242BH provides Hiccup Mode UnderVoltage Protection (UVP). When the FB voltage drops below 70% of the feedback reference voltage, the output voltage drops below the UVP trip threshold for longer than 250μs (typical) then IC's UVP is triggered. UVP function will be triggered to shut down switching operation. If the UVP condition remains for a period, the RT6242 will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period. Latch Mode For the RT6242AL/RT6242BL, it provides Latch-Off Mode Under Voltage Protection (UVP). When the FB voltage drops below 70% of the feedback reference voltage, the output voltage drops below the UVP trip threshold for longer than 250μs (typical) then IC's UVP is triggered. UVP function will be triggered to shut down switching operation. In shutdown condition, the RT6242 can be reset by EN pin or power input VIN. Current Limit The RT6242 current limit is a cycle-by-cycle “valley” type, measuring the inductor current through the synchronous rectifier during the off-time while the inductor current ramps down. The current is determined by measuring the voltage between source and drain of the synchronous rectifier. If the inductor current exceeds the current limit, the ontime one-shot is inhibited (Mask high side signal) until the inductor current ramps down below the current limit. Thus, only when the inductor current is well below the current limit is another on time permitted. This arrangement prevents the average output current from greatly exceeding the guaranteed current limit value, as typically occurs with other valley-type current limits. If the output current exceeds the available inductor current (controlled by the current limit mechanism), the output voltage will drop. If it drops below the output under-voltage protection level, the IC will enter UVP protection. The current limit of low side MOSFET is adjustable by an external resistor connected to the RLIM pin. The current Through extra resister RLIM connect to RLIM pin to setting the current limit value as Figure 7, below offer approximate formula equation for design reference : RLIM = 1 ILIM 106 5.588 107 Current Limit vs. RLIM 16 15 Current Limit (A) Output Under-Voltage Protection 14 13 12 11 10 65 70 75 80 85 90 95 100 105 RLIM (kΩ) Figure 7. Current Limit vs. RLIM Output Over-Voltage Protection If the output voltage VOUT rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on. For RT6242BL, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. If the output voltage still remains high, then IC's switches remain that the synchronous rectifier turns on and high-side MOS keeps off to operate at typical 500kHz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. If the output voltage exceeds the OVP trip threshold (1.2 times regulation level) for longer than 5μs (typical), then IC's output Over-Voltage Protection (OVP) is triggered. RT6242BL chip enters latch mode. For RT6242AL, if the output voltage VOUT rises above the regulation level and lower 1.2 times regulation level, the high-side switch naturally remains off and the synchronous rectifier turns on until the inductor current reaches zero current. If the output voltage remains high, then IC's switches remain off. If the output voltage exceeds the OVP limit range is from 6A to 16A. Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT6242A/B trip threshold (1.2 times regulation level) for longer than 5μs (typical), the IC's OVP is triggered. RT6242AL chip enters latch mode. For RT6242BH, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches the low side current limit. If the output voltage still remains high, the synchronous rectifier turns on and high-side MOSFET keeps off to operate at typical 500kHz switching protection, again if inductor current reaches low side current limit, the synchronous rectifier will turn off until next protection clock. RT6242BH is without OVP latch function and recover when OV condition release. For RT6242AH, if the output voltage remains high, the synchronous rectifier remains on until the inductor current reaches zero current. If the output voltage still remains high, then IC's switches remain off. RT6242AH is without OVP latch function and recover when OV condition release. Switching Frequency Setting The switching frequency can be set by using extra resister RRT. Switching frequency range is from 300kHz to 700kHz. Through extra resister RRT connect to RT pin to setting the switching frequency fSW as Figure 8, below offer approximate formula equation : Setting Frequency = fSW (kHz) 6 10 fSW 1.374 10 5 1.541 10 4 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 UQFN-16JL 3x3 (FC) package, the thermal resistance, θJA, is 27.6°C/W on a standard four-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) / (27.6°C/W) = 3.623W for UQFN-16JL 3x3 (FC) 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 9 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Frequency vs. RRT Resistor 700 650 Frequency (kHz)1 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 : 600 550 500 450 400 Maximum Power Dissipation (W)1 RRT = Thermal Considerations Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 350 0 300 100 115 130 145 160 175 190 205 220 235 250 RRT (k Ω) 25 50 75 100 125 Ambient Temperature (°C) Figure 9. Derating Curve of Maximum Power Dissipation Figure 8. Frequency vs. RRT Resistor Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Layout Consideration Follow the PCB layout guidelines for optimal performance of the device. Keep the traces of the main current paths as short and wide as possible. Put the input capacitor as close as possible to VIN and VIN pins. SW node is with high frequency voltage swing and should be kept at small area. Keep analog components away from the SW node to prevent stray capacitive noise pickup. Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the device. Connect all analog grounds to common node and then connect the common node to the power ground behind the output capacitors. An example of PCB layout guide is shown in Figure 10 and Figure 11 for reference. Internal Regulator Output. Connect a 1µF capacitor to GND to stabilize output voltage. The RRT resistor must be connected as close to the device as possible. Keep sensitive components away. The feedback components must be connected as close to the device as possible. R2 R1 VOUT CSS AGND FB RLIM 15 EN 14 SW 13 SW REN The RLIM resistor must be connected as close to the device as possible. Keep sensitive components away. VIN 7 GND RLIM 16 1 2 3 6 GND PVCC 5 VIN 4 VIN CIN RT SS Input capacitor must be placed as close to the IC as possible. AGND must be connected clear ground. 10 11 12 BOOT SW SW SW RPGOOD 9 8 PGOOD 5V SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace . CBOOT L COUT VOUT Power Good Indicator Open-Drain Output. The REN component must be connected. Connect IC Pin Trace as wide as possible for thermal consideration Add via for thermal consideration Keep sensitive components away from this CBOOT . Top Layer Figure 10. PCB Layout Guide (Top Layer) Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT6242A/B VIN GND Add via for thermal consideration Bottom Layer Figure 11. PCB Layout Guide (Bottom Layer) Suggested Inductors for Typical Application Circuit Component Supplier Part No. Inductance (H) DCR (m) Dimensions (mm) WE 7443320100 1 1.85 12.1 x 11.4 x 9.5 WE 744325120 1.2 1.8 10.2 x 10.2 x 4.7 CYNTEC CMMB104T-1R5MS 1.5 3.8 10.3 x 11.5 x 4 Recommended component selection for Typical Application. Component Supplier Part No. Capacitance (F) Case Size MURATA GRM31CR61E106K 10 1206 TDK C3225X5R1E106K 10 1206 TAIYO YUDEN TMK316BJ106ML 10 1206 MURATA GRM31CR60J476M 47 1206 TDK C3225X5R0J476M 47 1210 TAIYO YUDEN EMK325BJ476MM 47 1210 MURATA GRM32ER71C226M 22 1210 TDK C3225X5R1C226M 22 1210 Copyright © 2016 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 is a registered trademark of Richtek Technology Corporation. DS6242A/B-05 April 2016 RT6242A/B Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 0.500 0.600 0.020 0.024 A1 0.000 0.050 0.000 0.002 A3 0.100 0.175 0.004 0.007 D 2.900 3.100 0.114 0.122 E 2.900 3.100 0.114 0.122 b 0.320 0.420 0.013 0.017 b1 0.458 0.558 0.018 0.022 b2 0.200 0.300 0.008 0.012 L 2.325 2.425 0.092 0.095 L1 1.300 1.400 0.051 0.055 L2 0.325 0.425 0.013 0.017 L3 1.350 1.450 0.053 0.057 L4 0.350 0.450 0.014 0.018 e 0.500 0.020 K 0.325 0.013 K1 1.224 0.048 K2 2.175 0.086 K3 2.675 0.105 K4 0.785 0.031 K5 1.675 0.066 K6 2.175 0.086 K7 2.675 0.105 U-Type 16JL QFN 3x3 (FC) Package Copyright © 2016 Richtek Technology Corporation. All rights reserved. DS6242A/B-05 April 2016 is a registered trademark of Richtek Technology Corporation. www.richtek.com 19 RT6242A/B Footprint Information Package UQFN3*3 -16J(FC) Footprint Dimension (mm) Number Tolerance of Pin P 16 0.500 P1 P2 P3 Ay 0.951 0.899 0.890 3.800 By Ax C*12 2.200 3.800 0.800 C1 C2 2.775 1.750 C3*2 D*15 1.800 0.300 D1 K 0.508 0.675 K1 K2 0.715 0.250 ±0.050 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 20 DS6242A/B-05 April 2016