® RT7273 3-CH, 18V, Synchronous Step-Down Converter General Description The RT7273 features three synchronous wide input range high efficiency Buck converters. The converters are designed to simplify its application while giving the designer the option to optimize their usage according to the target application. The RT7273 also features a low power mode enabled by an external signal, which allows for a reduction on the input power supplied to the system when the host processor is in stand-by (low activity) mode. The converters can operate in 5V, 9V or 12V systems and have integrated power transistors. The output voltage can be set externally using a resistor divider to any value between 0.8V and the input supply minus 1V. Each converter features an enable pin that allows a delayed start-up for sequencing purposes, a soft-start pin that allows adjustable soft-start time by choosing the softstart capacitor, and a current limit pin (RLIMx) to adjust current limit by selecting an external resistor. The COMP pin allows optimizing transient versus dc accuracy response with a simple RC compensation. Features The switching frequency of the converters can either be set with an external resistor connected to ROSC pin or be synchronized to an external clock connected to SYNC pin if needed. The switching converters are designed to operate from 300kHz to 2.2MHz. The converters operate with 180° phase between CH 1 and CH 2, CH 3 (CH 2 and CH 3 ran in phase) to minimize the input filter requirements. Wide Input Supply Voltage Range : 4.5V to 18V Output Range : 0.8V to (VIN − 1V) Fully Integrated Triple-Buck Maximum Current 3.5A/2.5A/2.5A Continuous Operation 3A/2A/2A High Efficiency Switching Frequency 300kHz to 2.2MHz Set by External Resistor External Synchronization Pin for Oscillator External Enable/Sequencing Pins Adjustable Cycle-By-Cycle Current Limit Set by External Resistor Soft-Start Current Mode Control with Simple Compensation Circuit Power Good Indicator Discontinuous Operating Mode at Light Load when LOWP = High RoHS Compliant and Halogen Free Simplified Application Circuit VIN VINx VINR LX1 RT7273 ENx SYNC PGOOD LOWP SSx RLIMx VOUT1 FB1 LX2 VOUT2 FB2 LX3 VOUT3 ROSC GND Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 FB3 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7273 Applications Marking Information RT7273GQW : Product Number Set Top Boxes Blu-ray DVD DVR DTV Car Audio/Video Security Camera RT7273 GQW YMDNN YMDNN : Date Code Pin Configurations (TOP VIEW) EN3 BOOT3 VIN3 LX3 LX3 GND VINR VINR VINR GND Ordering Information RT7273 Package Type QW : WQFN-40L 6x6 (W-Type) (Exposed Pad-Option 2) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. 1 30 2 29 3 28 4 27 5 26 GND 6 25 7 24 8 41 9 10 23 22 21 GND VCC PVCC PGOOD GND LOWP FB2 COMP2 SS2 RLIM2 11 12 13 14 15 16 17 18 19 20 Suitable for use in SnPb or Pb-free soldering processes. EN1 BOOT1 VIN1 LX1 LX1 LX2 LX2 VIN2 BOOT2 EN2 40 39 38 37 36 35 34 33 32 31 RLIM3 SS3 COMP3 FB3 SYNC ROSC FB1 COMP1 SS1 RLIM1 WQFN-40L 6x6 Functional Pin Description Pin No. Pin Name Pin Function 1 RLIM3 Current Limit Setting for CH 3. Connect a resistor from RLIM3 to GND to set the peak current limit on the output inductor. 2 SS3 Soft-Start Time Setting for CH 3. Connect a capacitor to this pin and GND for soft-start time setting. 3 COMP3 Compensation Node for CH 3. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. 4 FB3 Feedback Voltage Input for CH 3. 5 SYNC Synchronous Clock Input. Connect to GND if not used. 6 ROSC Oscillator Setting. Connect a resistor from ROSC to GND to set the switching frequency. 7 FB1 Feedback Voltage Input for CH 1. 8 COMP1 Compensation Node for CH 1. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. 9 SS1 Soft-Start Time Setting for CH 1. Connect a capacitor to this pin and GND for soft-start time setting. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Pin No. Pin Name Pin Function 10 RLIM1 Current Limit Setting for CH 1. Connect a resistor from RLIM to GND to set the peak current limit on the output inductor. 11 EN1 Enable Control Input for CH 1. A low level signal on this pin disables it. If this pin is left open, a weak internal pull-up to VCC will allow automatic enables. 12 BOOT1 Bootstrap Supply for High-Side Gate Driver of CH 1. Connect a 0.1F ceramic capacitor from this pin to LX1. 13 VIN1 Power Input for CH 1 and Connected to High-Side MOSFET Drain. Place a 10F ceramic capacitor close to this pin. 14, 15 LX1 Switch Node of CH 1. 16, 17 LX2 Switch Node of CH 2. 18 VIN2 Power Input for CH 2. Place a 10F ceramic capacitor close to this pin. 19 BOOT2 Bootstrap Supply for High-Side Gate Driver of CH 2. Connect a 0.1F ceramic capacitor from this pin to LX2. 20 EN2 Enable Control Input for CH 2. A low level signal on this pin disables it. If this pin is left open, a weak internal pull-up to VCC will allow automatic enables. 21 RLIM2 22 SS2 23 COMP2 Compensation Node for CH 2. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. 24 FB2 Feedback Voltage Input for CH 2. 25 LOWP Discontinuous Operation Mode Input (Active High). GND Ground. The exposed pad must be connected to GND and soldered to a large PCB copper plane for maximum power dissipation. 27 PGOOD Power Good Indicator Output with Open-Drain. 28 PVCC 5V Power Supply Output. Connect a capacitor 10F between this pin and GND. 29 VCC 4.6V Power Supply Output. Connect a capacitor 3.3F between this pin and GND. 32, 33, 34 VINR Supply Voltage Input for Internal Control Circuit. 36, 37 LX3 Switch Output for CH 3. 38 VIN3 Power Input for CH 3. Place a 10F ceramic capacitor close to this pin. 39 BOOT3 Bootstrap Supply for High-Side Gate Driver of CH 3. Connect a 0.1F ceramic capacitor from this pin to LX3. 40 EN3 Enable Control Input for CH 3. A low level signal on this pin disables it. If this pin is left open, a weak internal pull-up to VCC will allow automatic enables. 26, 30, 31, 35, 41 (Exposed Pad) Current Limit Setting for CH 2. Connect a resistor from RLIM2 to GND to set the peak current limit on the output inductor. Soft-Start Time Setting for CH 2. Connect a capacitor to this pin and GND for soft-start time setting. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7273 Function Block Diagram Whole Chip Function Block Diagram Internal Regulator VINR PVCC VCC BOOT1 VIN1 EN1 RLIM1 SS1 CH 1 Step-Down Converter LX1 FB1 COMP1 ROSC SYNC VCC PVCC OSC BOOT2 VIN2 EN2 RLIM2 SS2 CH 2 Step-Down Converter LOWP VCC PVCC LX2 FB2 COMP2 GND BOOT3 CH 3 Step-Down Converter VIN3 EN3 RLIM3 SS3 PGOOD LX3 FB3 COMP3 Power Good Each Channel Function Block Diagram VCC VIN Slope Comp + Oscillator - RSENSE PVCC + 0.872V PGOOD Comparator 0.72V VCC SS 0.8V VCC Switch Controller + UV & PGOOD Comparator 6µA BOOT + +EA - SW + GND Current Comparator 1.5µA EN OC 5k + 3V 1.4V - Enable Comparator FB Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 COMP RLIM is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Operation Overall Oscillator The RT7273 is a 3-CH synchronous high voltage Buck Converter that can support the input voltage range from 4.5V to 18V and the output current up to 3A/2A/2A separately. The RT7273 uses an adjustable constant frequency, current-mode architecture. In normal operation, the high-side N-MOSFET is turned on when the Switch Controller is set by the Oscillator and is turned off when the current comparator resets the Switch Controller. While the high-side N-MOSFET is turned off, the low-side N-MOSFET is turned on. The frequency of internal oscillator can be adjusted by the external resistor at ROSC pin in the range between 300kHz and 2.2MHz. It can also be synchronized by an external clock in the range between 200kHz and 2.2MHz from SYNC pin. High-side N-MOSFET peak current is measured by internal RSENSE. The Current Signal is where Slope Compensator works together with sensing voltage of RSENSE. The error amplifier EA adjusts COMP voltage by comparing the feedback signal from the output voltage with the internal 0.8V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference, the COMP voltage then rises to allow higher inductor current to match the load current. UV and PGOOD Comparator If the feedback voltage (VFB) is higher than 0.72V and lower than 0.872V, the two comparators' output will go low and trigger Switch Controller to generate PGOOD signal for this channel. However, the whole chip PGOOD signal will go high only if all three channels' PGOOD conditions are established. If VFB is lower than UV threshold, the UV comparator's output will go high and the Switch Controller will turn off the high-side N-MOSFET. The output undervoltage protection is designed to operate in hiccup mode. This function is only available after soft-start finished. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 Enable Comparator The internal 1.5μA pull-up current to EN pin can be used to set the power sequence of each channel by connecting a capacitor to EN pin. Internal 5kΩ resistor and Zener diode are used to clamp the input signal to 3V. Thus, the EN pin can also be connected to VIN through a 100kΩ resistor. Soft-Start An internal current source (6μA) charges an external capacitor connected to SS pin to build the soft-start ramp voltage. The VFB voltage will track the soft-start ramp voltage during soft-start interval. The typical soft-start time is 2ms. Over-Current Limit Each channel can set its own over-current limit by external resistor. It is recommended that the over-current limit level should be 1.5 times larger than the maximum loading current. is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7273 Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN1, VIN2, VIN3, VINR ----------------------------------------------------------- −0.3V to 21V Switch Node Voltage, LX1, LX2, LX3 ------------------------------------------------------------------------ −0.3V to (VINx + 0.3V) < 10ns --------------------------------------------------------------------------------------------------------------- −5V to 25V BOOTx to LXx ----------------------------------------------------------------------------------------------------- −0.3V to 6V Other Pins --------------------------------------------------------------------------------------------------------- −0.3V to 6V Power Dissipation, PD @ TA = 25°C WQFN-40L 6x6 --------------------------------------------------------------------------------------------------- 3.52W Package Thermal Resistance (Note 2) WQFN-40L 6x6, θJA ---------------------------------------------------------------------------------------------- 28.4°C/W WQFN-40L 6x6, θJC --------------------------------------------------------------------------------------------- 5.3°C/W Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------- 260°C Junction Temperature -------------------------------------------------------------------------------------------- 150°C Storage Temperature Range ----------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------------------- 2kV Recommended Operating Conditions (Note 4) Supply Input Voltage -------------------------------------------------------------------------------------------- 4.5V to 18V Junction Temperature Range ----------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ----------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, fS = 800kHz, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Input Supply UVLO and Internal Supply Voltage Supply Current (Shutdown) IQ_SDN VEN = 0V for All CHs -- 1.3 -- mA Supply Current (Quiescent) IQ Converters enabled, Buck1 = 3.3V, Buck2 = 2.5V, Buck3 = 7.5V -- 20 -- mA Supply Current (LOWP enabled) IQ_LOWP Converters enabled, Buck1 = 3.3V, Buck2 = 2.5V, Buck3 = 7.5V -- 1.5 -- mA VIN Under-Voltage Lockout VVIN_UVLO VIN Rising -- 4.2 -- V VIN Falling -- 200 -- mV -- 100 -- s VIN Under-Voltage Lockout Hysteresis VIN Under-Voltage Lockout Deglitch Internal Biasing Supply VPVCC -- 5 -- V Internal Biasing Supply VVCC -- 4.6 -- V PVCC Under-Voltage Lockout VPVCC_UVLO -- 3.8 -- V -- 250 -- mV PVCC Rising PVCC Under-Voltage Lockout Hysteresis Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Parameter Symbol Test Conditions PVCC Under-Voltage Lockout Deglitch Min Typ Max Unit -- 100 -- s Enable Circuit, Soft-Start, Sync Circuit, Low Power Mode and Switching Frequency Logic-High VEN_H 1.6 -- -- Logic-Low VEN_L -- -- 1.2 ENx Pull-Up Current IEN -- 1.5 -- A Soft-Start Current Source ISS -- 6 -- A Converter Switching Frequency Range fSW 0.3 -- 2.2 MHz Frequency Setting Resistor ROSC 50 -- 600 k Internal Oscillator Accuracy fSW_TOL 10 -- 10 % Enable Input Voltage fSW = 800kHz V Logic-High VSYNC_H 1.6 -- -- Logic-Low VSYNC_L -- -- 1.2 fSW_SYNC 0.2 -- 2.2 MHz SYNC Signal Minimum Duty Cycle 10 -- -- % SYNC Signal Maximum Duty Cycle -- -- 90 % SYNC External Clock Input Voltage Synchronization Range Low Power Mode Input Voltage Logic-High VLOWP_H 1.6 -- -- Logic-Low VLOWP_L -- -- 1.2 0.792 0.8 0.808 0.784 0.8 0.816 V V Feedback V Feedback Reference Voltage VREF Minimum On-Time tON(MIN) -- 100 -- ns Minimum Off-Time tOFF(MIN) -- 100 -- ns RDS(ON)1_H -- 95 -- RDS(ON)1_L -- 50 -- RDS(ON)2_H -- 120 -- RDS(ON)2_L -- 80 -- RDS(ON)3_H -- 120 -- RDS(ON)3_L -- 80 -- IOC_CH1 2 -- 6 A 2 -- 5 A 4.5V VIN 18V CH 1 On-Resistance Switch On-Resistance m CH 2 On-Resistance Switch On-Resistance m CH 3 On-Resistance Switch On-Resistance m Current Limit Current Limit CH 1 Current Limit CH 2, CH 3 Range IOC_CH2, CH3_Range Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7273 Parameter Current Limit CH 1 Current Limit CH 2, CH 3 Symbol IOC_CH1 IOC_CH2, CH3 Test Conditions Min Typ Max RLIM1 = 37k 2.4 3 -- RLIM1 = 50k 3.4 4 -- RLIM1 = 63k 4.25 5 -- RLIM2, LIM3 = 44k 1.6 2 -- RLIM2, LIM3 = 69k 2.55 3 -- RLIM2, LIM3 = 94k 3.4 4 -- Unit A A Regulation Line Regulation VIN = 4.5V to 18V, IOUT = 1000mA -- 0.5 -- %VOUT Load Regulation IOUT = 10% to 90%, IOUT_MAX -- 0.5 -- %VOUT /A Error Amplifier Error Amplifier Transconductance GEA -- 250 -- A/V Comp to Current Sense Transconductance GCS -- 4 -- A/V Output Falling (device will be disabled after tON_HICCUP) -- 85 -- Output Rising (PGOOD will be asserted) -- 90 -- Power Good Reset Generator Under-Voltage Threshold VUV_CHx % Under-Voltage Deglitch Time tUV_DEGLITCH Each Channel Buck -- 10 -- ms Hiccup Mode On-Time tON_HICCUP VUV_CHx asserted -- 10 -- ms Hiccup Mode Off-Time tOFF_HICCUP All Bucks disable during tOFF_HICCUP before re-start is attempted. -- 15 -- ms Power Good tPGOOD Power good delay time after all bucks power-up successfully -- 640 -- ms Thermal Shutdown Thermal Shutdown Threshold TSD -- 150 -- °C Thermal Shutdown Hysteresis T SD -- 20 -- °C 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 © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Typical Application Circuit 32, 33, 34 VIN 12V C33 10µF C23 22µF 13 C10 10µF 18 C17 10µF R5 20k C2 4.7nF R17 20k C28 4.7nF R3 20k C1 4.7nF C19 NC C20 NC C14 NC R1 51k R16 75k R4 82k C4 4.7nF C25 4.7nF C3 4.7nF VIN1 RT7273 LX1 VIN2 14, 15 28 PVCC 29 VCC LX2 C27 3.3µF 8 COMP1 10 RLIM1 9 SS1 11 EN1 LX3 C24 100nF L2 4.7µH 36, 37 C31 100nF L3 4.7µH 27 C13 470pF R12 80.8k C18 22µF C3 22µF VOUT2 1.8V/2A C32 470pF R15 32.4k R20 40.2k C21 22µF C16 22µF VOUT3 3.3V/2A C15 470pF C22 22µF C11 22µF R13 12.7k VCC PGOOD VOUT1 1.2V/3A R1 40.2k FB3 4 3 COMP3 1 RLIM3 2 SS3 40 EN3 C6 4.7nF 16, 17 FB2 24 BOOT3 39 C5 4.7nF 23 COMP2 21 RLIM2 22 SS2 20 EN2 C29 4.7nF C7 100nF L1 4.7µH R9 40.2k FB1 7 BOOT2 19 38 VIN3 C9 10µF C26 10µF BOOT1 12 VINR R18 100k PGOOD SYNC 5 LOWP 25 Input Signal ROSC 6 GND 26, 30, 31, 35, 41 (Exposed Pad) R7 383k Table 1. Suggested Component Values for CH1 (VIN = 12V, fS = 500kHz) VOUT (V) R9 (k) R12 (k) C13 (pF) R5 (k) C2 (nF) L1 (H) C3 (F) 1.2 40.2 80.8 470 20 4.7 4.7 44 1.8 40.2 32.4 470 20 4.7 4.7 44 3.3 40.2 12.7 470 20 4.7 4.7 44 5 40.2 7.6 470 24 5.6 6.8 44 7 40.2 5.2 470 24 5.6 6.8 44 Note 5. The suggested component values can be applied to CH 2 and CH 3 as well. Note 6. Above values are fully tested for stable operation. When making changes to output capacitors or switching frequency, please follow the guidelines in the application section. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7273 Typical Operating Characteristics Buck 1 Efficiency vs. Load Current 100 Output Voltage vs. Load Current 1.210 LOWP = 0 90 1.205 Output Voltage (V) 80 Efficiency (%) LOWP = 0 70 60 VIN = 5V VIN = 12V VIN = 17V 50 40 30 1.200 1.195 1.190 20 VIN = 17V VIN = 12V VIN = 5V 1.185 10 VOUT = 1.2V, L = 4.7μH, fS = 500kHz VOUT = 1.2V, L = 4.7μH, fS = 500kHz 0 1.180 0 0.5 1 1.5 2 2.5 3 0 0.5 1 Load Current (A) 2.5 3 Output Voltage vs. Input Voltage Output Voltage vs. Temperature 1.21 Output Voltage (V) 1.21 1.20 1.19 VIN = 17V VIN = 12V VIN = 5V 1.18 1.20 1.19 1.18 VOUT = 1.2V, IOUT = 1A VOUT = 1.2V, IOUT = 0A 1.17 1.17 -50 -25 0 25 50 75 100 125 5 7 9 11 13 15 17 Input Voltage (V) Temperature (°C) Current Limit vs. Input Voltage Current Limit vs. Temperature 5.5 5.5 5.0 5.0 Current Limit (A) Current Limit (A) 2 Load Current (A) 1.22 Output Voltage (V) 1.5 4.5 4.0 VIN = 5V VIN = 12V VIN = 17V 4.5 4.0 VOUT = 0V, RLIM1 = 68kΩ 3.5 VOUT = 0V, RLIM1 = 68kΩ 3.5 5 7 9 11 13 15 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 17 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Power On from VIN Power Off from VIN VIN (20V/Div) VIN (20V/Div) VOUT (1V/Div) VOUT (1V/Div) VLX1 (10V/Div) VLX1 (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 3A VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (4ms/Div) Time (4ms/Div) Power On from EN Power Off from EN VEN (10V/Div) VEN (10V/Div) VOUT (1V/Div) VOUT (1V/Div) VLX1 (10V/Div) VLX1 (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 3A VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (4ms/Div) Time (4ms/Div) Load Transient Response Output Ripple LOWP = 0 VOUT (500mV/Div) VLX1 (10V/Div) VOUT (10mV/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 0 to 3A Time (100μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7273 Buck 2 Efficiency vs. Load Current 100 Output Voltage vs. Load Current 1.800 LOWP = 0 90 Output Voltage (V) Efficiency (%) 80 70 60 VIN = 5V VIN = 12V VIN = 17V 50 40 30 20 10 LOWP = 0 1.795 VIN = 5V VIN = 12V VIN = 17V 1.790 1.785 VOUT = 1.8V VOUT = 1.8V, L = 4.7μH, fS = 500kHz 0 1.780 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 0.75 Load Current (A) Reference Voltage vs. Temperature 0.805 1.80 0.800 VIN = 17V VIN = 12V VIN = 5V 1.75 2 1.79 1.78 VOUT = 1.8V, IOUT = 0A VOUT = 1.8V, IOUT = 1A 0.790 1.77 -50 -25 0 25 50 75 100 125 5 7 Temperature (°C) 9 11 13 15 17 Input Voltage (V) Current Limit vs. Input Voltage Current Limit vs. Temperature 4.0 4.5 3.5 4.0 Current Limit (A) Current Limit (A) 1.5 Output Voltage vs. Input Voltage 1.81 Output Voltage (V) Reference Voltage (V) 1.25 Load Current (A) 0.810 0.795 1 3.0 2.5 3.5 VIN = 5V VIN = 12V VIN = 17V 3.0 VOUT = 0V, RLIM2 = 82kΩ VOUT = 0V, RLIM2 = 82kΩ 2.0 2.5 5 7 9 11 13 15 Input voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 17 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Power On from VIN Power Off from VIN VIN (20V/Div) VIN (20V/Div) VOUT (2V/Div) VOUT (2V/Div) VLX2 (10V/Div) VLX2 (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.8V, IOUT = 2A VIN = 12V, VOUT = 1.8V, IOUT = 2A Time (4ms/Div) Time (4ms/Div) Power On from EN Power Off from EN VEN (10V/Div) VEN (10V/Div) VOUT (2V/Div) VOUT (2V/Div) VLX2 (10V/Div) VLX2 (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.8V, IOUT = 2A VIN = 12V, VOUT = 1.8V, IOUT = 2A Time (4ms/Div) Time (4ms/Div) Load Transient Response Output Ripple LOWP = 0 VOUT (500mV/Div) VLX2 (10V/Div) VOUT (10mV/Div) IOUT (2A/Div) VIN = 12V, VOUT = 1.8V, IOUT = 0 to 2A Time (100μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 VIN = 12V, VOUT = 1.8V, IOUT = 2A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT7273 Buck 3 Efficiency vs. Load Current Output Voltage vs. Load Current 100 3.350 LOWP = 0 90 LOWP = 0 Output Voltage (V) Efficiency (%) 80 70 60 VIN = 5V VIN = 12V VIN = 17V 50 40 30 20 10 3.345 VIN = 17V VIN = 12V VIN = 5V 3.340 3.335 VOUT = 3.3V, L = 4.7μH, fS = 500kHz VOUT = 3.3V 0 3.330 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 0 0.25 0.5 Load Current (A) 1 1.25 1.5 1.75 2 Load Current (A) Reference Voltage vs. Temperature Output Voltage vs. Input Voltage 0.810 3.350 3.345 0.805 Output Voltage (V) Reference Voltage (V) 0.75 0.800 VIN = 17V VIN = 12V VIN = 5V 0.795 3.340 3.335 3.330 3.325 VOUT = 3.3V, IOUT = 0A 0.790 VOUT = 3.3V, IOUT = 1A 3.320 -50 -25 0 25 50 75 100 5 125 7 9 Temperature (°C) 3.5 4.0 3.0 2.5 VOUT = 0V, RLIM3 = 82kΩ 5 7 9 11 13 15 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 13 15 17 Currrent Limit vs. Temperature 4.5 Currrent Limit (A) Current Limit (A) Current Limit vs. Input Voltage 4.0 2.0 11 Input Voltage (V) 17 3.5 VIN = 17V VIN = 12V VIN = 5V 3.0 VOUT = 0V, RLIM3 = 82kΩ 2.5 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Power Off from VIN Power On from VIN VIN (20V/Div) VIN (20V/Div) VOUT (2V/Div) VOUT (2V/Div) VLX3 (10V/Div) VLX3 (10V/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (4ms/Div) Time (4ms/Div) Power On from EN Power Off from EN VEN (10V/Div) VEN (10V/Div) VOUT (2V/Div) VOUT (2V/Div) VLX3 (10V/Div) VLX3 (10V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (4ms/Div) Time (4ms/Div) Load Transient Response Output Ripple LOWP = 0 VOUT (500mV/Div) VLX3 (10V/Div) VOUT (10mV/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0 to 2A Time (100μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT7273 Overall Quiescent Current vs. Temperature UVLO vs. Temperature 4.3 Rising 4.2 27 VIN = 17V VIN = 12V VIN = 5V UVLO (V) Quiescent Current (mA) 31 23 19 4.1 Falling 4.0 3.9 VOUT = 1.2V 15 VIN = 12V, VOUT = 1.2V 3.8 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 125 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Application Information Adjustable Switching Frequency To select the internal switching frequency connect a resistor from ROSC to ground. Figure 1 shows the required can be higher or lower than the external clock signal. When synchronization is not applied, the SYNC pin should be connected to ground. resistance for a given switching frequency. Out-of-Phase Operation 1100 CH 1 has a low conduction resistance compared to CH 2 and 3. Normally CH 1 is used to drive higher system loads. CH 2 and 3 are used to drive some peripheral loads like I/ O and line drivers. The combination of CH 2 and 3's loads may be on par with CH 1's. In order to reduce input ripple current, CH 2 operates in phase with CH 3; CH 1 and CH 2 operate 180 degrees out-of-phase as shown in Figure 2. This enables the system to have less input ripple, lower component cost, save board space and reduce EMI. 1000 900 ROSC (kΩ) 800 700 600 500 400 300 200 100 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Out-of-Phase Operation Switching Frequency (MHz) Figure 1. ROSC vs. Switching Frequency ROSC (k) = 174 f 1.122 VLX1 (10V/Div) For operation at 500kHz a 383kΩ resistor is required. Generally, 500kHz switching frequency is a good value to achieve both small solution size and high efficiency operation. Higher frequency allows even smaller components, but the drawback is that it lowers system efficiency due to higher switch losses. Minimum on-time must also be considered : minimum duty cycle is given by tON(MIN) x fSW, so at higher frequency, very low output voltages may not be possible due to duty cycle limit. When increasing switching frequency, inductor value can be reduced in the same ratio, keeping current ripple constant. Higher frequency operation with smaller inductors will also require a lower value of compensation resistor. Synchronization The status of the SYNC pin will be ignored during start-up and the RT7273's control will only synchronize to an external signal after the PGOOD signal is asserted. The RT7273 can be easily synchronized to an external clock signal by applying a 200kHz to 2.2MHz square-wave signal to the SYNC input. After external synchronization is applied, the internal oscillator setting will be ignored. It Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 VLX2 (10V/Div) VLX3 (10V/Div) VIN = 12V, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 3.3V, IOUT = 1A Time (1μs/Div) Figure 2. Switching Signals for Each Channel Soft-Start Time The device has an internal pull-up current source of 6μA that charges an external slow start capacitor to implement a slow start time. The equation shows how to select a slow-start capacitor based on an expected slow start time. The voltage reference (VREF) is 0.8V and the slow start charge current (ISS) is 6μA. The soft-start circuit requires 1nF per 133μs to be connected at the SS pin. A 0.625ms soft-start time is implemented for all converters fitting 4.7nF to the relevant pins. C (nF) TSS (ms) = VREF (V) SS ISS (μA) is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT7273 Adjusting the Output Voltage Power Good The output voltage is set with a resistor divider from the output node to the FB pin as shown in Figure 3. It is recommended to use 1% tolerance or better divider resistors. In order to improve efficiency at light load, start with 40.2kΩ for the R1 resistor and use the equation to calculate R2. 0.8V R2 = R1 ( ) VOUT 0.8V The PGOOD pin is an open-drain output. The PGOOD pin is pulled low when any Buck converter is pulled below 85% of the nominal output voltage. The PGOOD is pulled up when all three Buck converters' outputs are more than 90% of its nominal output voltage and reset time of 1 second elapses. VOUT RT7273 R1 FB R2 Over-Current Limit The RT7273 current limit trip is set as shown in Figure 4 and Figure 5. 6.0 - 0.8V 5.5 + Figure 3. Voltage Divider Circuit Bootstrap Capacitor The device adopts three bootstrap power supply with a small ceramic capacitor between the BST and LX pins to provide the gate drive voltage for the high-side MOSFET. The value of the ceramic capacitor should be 0.1μF. A ceramic capacitor with an X7R or X5R grade dielectric is recommended because of the stable characteristics over temperature and voltage. Current Limit (A) 5.0 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 4.0 3.5 3.0 2.5 2.0 1.5 20 30 40 50 60 70 80 RLIM ) (kΩ) LIM (k Figure 4. Channel 1 Current Limit vs. RLIM 6.0 Output Capacitor Selection 5.0 Current Limit (A) For the output capacitors, ceramic capacitors are recommended due to their small size and low ESR. Recommended output capacitance for all Buck channels is 44μF (two 22μF ceramic capacitors in parallel) which provides sufficiently low voltage ripple for most applications. When using different output capacitance, it is important to realize that system stability will be influenced. As a general guideline, when reducing output capacitance of a certain channel, the compensation resistor of that channel must be reduced in same ratio to maintain stable operation. As an example, when using 22μF instead of 44μF output capacitance for CH 1, the compensation resistor R5 must be reduced from 20kΩ to 10kΩ. 4.5 4.0 3.0 2.0 1.0 30 40 50 60 70 80 90 100 110 120 R ) RLIM (kΩ) LIM (k Figure 5. Channel 2 and Channel 3 Current Limit vs. RLIM is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Example : CH 1, 12V input, 1.2V output and 500kHz application, using 4.7μH inductor, and max load current is 3.1A. V V Inductor ripple current = IL = OUT 1 OUT = f L VIN 0.46A , so half of the ripple = 0.23A Power Dissipation For recommended operating condition specifications, the maximum junction temperature inside RT7273 is 125°C. The maximum power dissipation depends on the thermal resistance of the IC package and the PCB layout, the rate of surrounding airflow and the ambient temperature. The following procedure can be used to calculate the junction temperature of RT7273 under continuous loading at switching frequency of 500kHz. Define the desired output and input voltage for each converter. Define the maximum continuous loading on each converter, not exceeding the maximum continuous loading. Find the expected losses (W) in each converter inside the RT7273 from the graphs below. Max inductor peak current = 3.1 + 0.23 = 3.33A Current limit should be at least 15% higher than 3.33A, so ILIM = 4A is recommended. According to Figure 4, a 50kΩ resistor RLIM is required. All converters operate in hiccup mode under voltage protection. When an over-current or short circuit occurs lasting more than 10ms in any of the converters, all converters will be disable for 10ms. Once hiccup mode off time elapses, the start-up sequence will be tried again. A normal start-up will resume as soon as the overload or short circuit is removed. If any of the converters sees another over-current or short circuit event, the hiccup mode protection will be triggered until the failure is cleared. No global hiccup mode will occur if an over-current or short circuit event occurs less than 10ms. Only the relevant converter affected will be protected by the cycle-by-cycle current limit during the event. Power Sequence via Capacitor on Enable Pins Connecting a capacitor to the EN pin of a channel will add a start-up delay for this channel. A specific start-up power sequence of Channel 1/2/3 can be achieved by using different values of capacitors on the EN1/EN2/EN3 pins. The channel start-up delay is around 1.4ms per nF capacitance on the EN pin. The losses depend on the input supply, output voltage, switching frequency and the chosen converter. The junction temperature inside the RT7273 can be calculated by the following formula: TJ = TA + PD x θJA where TJ is the junction temperature, TA is the ambient temperature, PD is the sum of losses in all converters and θJA is the junction to ambient thermal resistance. 1.8 1.6 1.4 1.2 Loss (W) The current limit value set by the RLIM resistors refers to the peak current in the inductor. Output load current is the average value of the inductor current. So when setting a current limit of a Buck channel to meet a certain max load requirement, the current limit must be set sufficiently high to include at least 50% of the inductor current ripple and 15% tolerance on the current limit. 1.0 VIN = 17V VIN = 12V VIN = 5V 0.8 0.6 0.4 0.2 VOUT = 1.2V, fS = 500kHz 0.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 Load Current (A) Figure 6. Channel 1 Loss vs. Load Current Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 19 RT7273 1.8 Thermal Considerations 1.6 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 : 1.4 VIN = 17V VIN = 12V VIN = 5V 1.0 0.8 0.6 0.4 0.2 PD(MAX) = (TJ(MAX) − TA) / θJA VOUT = 1.8V, fS = 500kHz 0.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 Load Current (A) Figure 7. Channel 2 Loss vs. Load Current For recommended operating condition specifications, the maximum junction temperature is 125°C . The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-40L 6x6 package, the thermal resistance, θJA, is 1.8 1.6 1.4 28.4°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : Loss (W) 1.2 VIN = 17V VIN = 12V VIN = 5V 1.0 0.8 where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. PD(MAX) = (125°C − 25°C) / (28.4°C/W) = 3.52W for WQFN-40L 6x6 package 0.6 0.4 0.2 VOUT = 3.3V, fS = 500kHz 0.0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 Load Current (A) Figure 8. Channel 3 Loss vs. Load Current Thermal Shutdown The RT7273 includes an over temperature protection (OTP) circuitry to prevent overheating due to excessive power dissipation. The OTP will shut down switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by 20°C the IC will resume normal operation with a complete soft-start. For continuous operation, provide adequate cooling so that the junction temperature does not exceed 150°C. 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 Maximum Power Dissipation (W)1 Loss (W) 1.2 Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 9. Derating Curve of Maximum Power Dissipation Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 20 is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 Layout Consideration GND Place the input and output capacitors as close to the IC as possible. CIN3 COUT3 CIN VOUT3 LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. L3 EN3 BOOT3 VIN3 LX3 LX3 GND VINR VINR VINR GND LX3 CBOOT3 RLIM3 40 39 38 37 36 35 34 33 32 31 CC3 R C3 VOUT3 R20 Place the feedback GND as close to the IC as possible for better R9 regulation. VOUT1 GND R13 ROSC R12 CC1 RC1 CSS1 RLIM1 RLIM3 SS3 COMP3 FB3 SYNC ROSC FB1 COMP1 SS1 RLIM1 1 30 2 29 3 28 4 27 5 26 GND 6 25 7 24 8 23 41 9 22 10 21 GND VCC PVCC PGOOD GND LOWP FB2 COMP2 SS2 RLIM2 11 12 13 14 15 16 17 18 19 20 LX1 CBOOT2 CBOOT1 CIN1 L1 CVCC CPVCC R15 R1 RC2 CSS2 CC2 Place the feedback as close to the IC as possible for better regulation. VOUT2 GND RLIM2 EN1 BOOT1 VIN1 LX1 LX1 LX2 LX2 VIN2 BOOT2 EN2 CSS3 GND LX2 L2 VOUT1 VOUT2 COUT1 C CIN2 OUT2 GND Place the input and output capacitors as close to the IC as possible. Figure 10. PCB Layout Guide Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS7273-04 October 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 21 RT7273 Outline Dimension 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches 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 5.950 6.050 0.234 0.238 Option1 4.000 4.750 0.157 0.187 Option2 3.470 3.570 0.137 0.141 5.950 6.050 0.234 0.238 Option1 4.000 4.750 0.157 0.187 Option2 2.570 2.670 0.101 0.105 D2 E E2 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 40L QFN 6x6 Package Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 22 is a registered trademark of Richtek Technology Corporation. DS7273-04 October 2014 RT7273 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. DS7273-04 October 2014 www.richtek.com 23