Selection Guide SG002–Oct 2015 ACOT™ (Advanced Constant-On Time) Synchronous Step-Down Converters Introducing our new cost-effective, high performance ACOT Buck converters for Set Top Boxes, Industrial and commercial low power systems, computer peripherals and LCD Monitors and TVs. ACOT Key Features The proprietary ACOT control scheme not only features ultra-fast transient response but also improves upon legacy constant on-time architectures, achieving constant average frequency over line, load and output ranges to minimize interference and noise problems. The ACOT Buck converters are stable with and optimized for ceramic output capacitors without external ripple injection scheme. The ACOT family includes latch-off, hiccup and constant current protection modes. Richtek ACOT™ (Advanced Constant On Time) Synchronous Step-Down Converter Constant Frequency MLCC Suitable Frequency Locked Loop (FLL) Pulse Shaping Regulators (PSR™) provides constant average frequency supports MLCC-only operation with over line & load. lowest component count. Ultrafast Transient Response T-on control with ‘’instant on’’ response provides ultrafast transient response. SG002-00 OCT 2015 © 2015 Richtek Technology Corporation 1 Selection Guide Comparison Table of Richtek Buck Topologies Topology CMCOT Current Mode Constant-On-Time Current Mode ACOT Advanced Constant-On-Time Response to Load Steps moderate fast extremely fast Current Sense current sense limits min. ON time low side current sense not required Min. ON Time larger, limits the min. achievable duty-cycle small min. On time allows small duty-cycles small min. On time allows small duty-cycles Frequency stable fixed f SW constant average f SW constant average fSW Stable with MLCC √ √ √ Slope Compensation √ not required not required Synchronized to ext. Clock √ x x used for applications with steady load conditions. (some CM buck converters can be synchronized to an external clock) used in applications with moderate load transients, or applications that require small minimum ON times (i.e. high switching frequency in combination with larger step-down ratios) applications with severe fast load transients , such as DDR, Core SoC, FPGA and ASIC supplies Applications Which Buck topology is most suitable for your application? Input voltage, output voltage and nature of the load will in most cases determine which topology is most suitable. Systems with steady load conditions can use CM buck converter. To avoid sensitive frequency bands, some CM buck converters can be synchronized to an external clock. Applications with severe fast load transients (such as seen in Core and DDR rails), should be driven by ACOT buck converters. Note that switching frequency can deviate considerably during dynamic loads. CMCOT buck converter performance lies in between CM and ACOT buck converters, so it can be used in applications with moderate load transients, or applications that require small minimum ON times (i.e. high switching frequency in combination with larger step-down ratios). The dynamic frequency deviation during load transients is less than ACOT. For more information, please read the application notes ’’Comparing Buck converter topologies’’ and ’’Choosing the optimal Buck converter for your application’’. SG002-00 OCT 2015 © 2015 Richtek Technology Corporation 2 Selection Guide Example of ACOT™ Product Overview: RT7275 & RT7276 3A, 4.5V to 18V VIN, 700kHz ACOT™ Synchronous Step-Down Converter RT7275/76 datasheet download (PDF, 356KB) Simplified Application Circuit Ultra Fast Transient Response RT7275: Steady 700kHz Switching Frequency at all loads RT7276: Steady 700kHz Switching Frequency in continuous conduction mode Internal 90mΩ Switch and 60mΩ Synchronous Rectifier 0.765V to 8V Adjustable Output Voltage Optional Output Discharge Function(TSSOP-14 only) Power Good Indication Externally-adjustable, Pre-biased compatible Soft-Start Cycle-by-cycle current limit Current Limit with Latch-off Mode Under-Voltage Protection(TSSOP-14); Current Limit with Hiccup Mode Under-Voltage Protection (DFN-10L 3x3) Output Over-Voltage Protection Pin Configurations EN FB PVCC SS PGOOD 1 2 3 4 5 PGND Features 11 10 9 8 7 9 Datasheet VIN VIN BOOT SW SW WDFN-10L 3x3 SG002-00 OCT 2015 © 2015 Richtek Technology Corporation VOUT FB PVCC SS GND PGOOD EN 14 2 13 3 4 12 PGND 5 6 7 11 10 15 9 8 VINR VIN BOOT SW SW PGND PGND TSSOP-14 (Exposed Pad) 3 Selection Guide ACOT™ Product Family and Sample Ordering Information VIN range up to 6.0V, IOUT up to 2A Key features: Power Good, low quiescent current, and ±2% VREF VIN Current rating Package f SW Over current behaviour IQ P/N PSM/PWM Force-PWM For enhanced light load efficiency 2.5V-6.0V 2A EN FB AGND VOUT 1 8 2 7 3 6 4 5 1.5MHz PGOOD VIN LX PGND Cycle-by-cycle Current limit 22µA *Coming soon *Coming soon RT5784A RT5784B RT5785A*Coming soon RT5785B*Coming soon RT5795A - AGND 7 6 5 2 3 4 PGND VIN LX VOUT FB 8 PGOOD EN WDFN-8JL 2x1.5 (FC) 2.5V-5.5V EN PGND AGND FB PGND TSOT-23-8 (FC) 1 2 3 4 VIN LX PGOOD VOS 8 7 6 5 9 2.7MHz 30µA WDFN-8SL 2x2 VIN rangeup to 18.0V, IOUT up to 3A in SOT-23 and WDFN 2x3 small packages Key features: simple and easy low BOM cost design with excellent FCOL thermal performance, 500kHz f SW and ±1.5% VREF EN PGOOD 8 7 6 5 2 3 4 Over current behaviour P/N Hiccup PSM/PWM For enhanced light load efficiency Constant current Force-PWM RT7255A ✓ ✓ RT7255B RT7255C ✓ RT7255D ✓ FB SS 1.5A VIN Package BOOT 4.3V-18V Current rating GND VIN SW SOT-23-8 2A 2.5A (3Apeak) 3A 4.3V-18V 1.5A BOOT GND LX VIN 1 2 3 4 GND 4.5V-18V 9 8 7 6 5 SS PGOOD EN FB ✓ RT6232A RT6232B ✓ RT6233A RT6233B ✓ RT6234A*Coming soon RT6234B*Coming soon ✓ RT7285/A WDFN-8L 2x3 SW VIN EN 6 5 4 2 3 BOOT GND FB ✓ 4.5V-18V 1.5A 6 EN BOOT 5 4 2 3 RT7285C ✓ T/SOT-23-6 FB RT7285B RT7285D ✓ RT6211A ✓ RT6211B ✓ VIN GND LX SOT-23-6 4.3V-18V 2.5A (3A peak) SW VIN EN 6 5 4 2 3 BOOT GND FB ✓ 2A BOOT EN 6 2.5A (3A peak) 4.3V-18V 3A (3.5A peak) FB ✓ 2 3 ✓ SW VIN EN 6 5 4 2 3 BOOT GND FB 3A BOOT EN 6 FB 5 4 2 3 RT6212B RT6213A RT6213B ✓ RT7295A ✓ ✓ RT7295B RT7295C ✓ TSOT-23-6 (FC) 4.5V-18V RT7294D RT6212A ✓ 4 GND LX VIN RT7294C ✓ 5 TSOT-23-6 (FC) RT7294B ✓ TSOT-23-6 (FC) 4.5V-18V RT7294A ✓ RT7295D ✓ ✓ ✓ RT6214A RT6214B GND LX VIN TSOT-23-6 (FC) SG002-00 OCT 2015 © 2015 Richtek Technology Corporation 4 Selection Guide VIN range up to 18.0V, IOUT up to 5.5A in TSSOP-14, WDFN and SOP-8 packages Key features: high performance, programmable Soft-Start, Power Good in TSSOP-14 & WDFN-10L 3x3, 650kHz f SW and ±1% VREF VIN Current Package Features rating Over current behaviour P/N VOUT Discharge function Latch-off Constant PSM/PWM current For enhanced light ✓ ✓ ✓ RT7280GCP RT7279GCP ✓ ✓ ✓ RT7276GCP RT7275GCP ✓ ✓ ✓ RT7232GCP RT7231GCP ✓ ✓ ✓ RT7236GCP RT7235GCP Power Good 4.5V-18V 2A 3A 4A 5A VOUT FB PVCC SS GND PGOOD EN VINR VIN BOOT SW SW PGND PGND 14 2 13 3 12 PGND 4 11 5 10 6 9 15 7 8 TSSOP-14 (Exposed Pad) 2A 4A 5A 1 2 3 10 9 PGND 3A EN FB PVCC SS PGOOD 4 5 8 7 6 11 VIN VIN BOOT SW SW WDFN-10L 3x3 5.5A Force-PWM load efficiency ✓ ✓ RT7280GQW RT7279GQW ✓ ✓ RT7276GQW RT7275GQW ✓ ✓ RT7232GQW RT7231GQW ✓ ✓ RT7236GQW RT7235GQW ✓ ✓ RT6206BHGQW RT6206AHGQW 2A ✓ RT7274GSP RT7281GSP 3A ✓ RT7278GSP RT7277GSP ✓ RT7234GSP RT7233GSP RT6201AHGSP RT6201BHGSP RT7240GSP RT7239GSP 4A EN FB 2 4A PVCC 3 SS 4 5A Hiccup 8 GND VIN 7 BOOT 6 SW 5 GND 9 ✓ ✓ SOP-8 (Exposed Pad) 5A ✓ RT6202AHGSP RT6202BHGSP 5.5A ✓ RT6206BHGSP RT6206AHGSP VIN range up to 18.0V, IOUT up to 12A in UQFN packages Key features: high current ACOT parts, programmable Soft-Start, Power Good, FCOL technology for low parasitic and good thermal performance and ±1.0% VREF VIN Current rating Package f SW Over current behaviour RON P/N PSM/PWM Force-PWM For enhanced light load BOOT 6A SW 4.5V-18V 5A GND efficiency 13 12 11 650kHz GND 1 10 VIN EN 2 9 VIN FB 3 8 PGOOD NC 4 7 NC 60m/22m RT6207A RT6207B 51m/18m RT6236A RT6236B 40m/16m RT6237A RT6237B 35m/14m RT6238A RT6238B 30m/12m RT6239A RT6239B 12m/5.4m RT6242A RT6242B 6 PVCC SS 5 Cycle-by-cycle Current limit GND 13 12 500kHz 1 11 GND FB 2 10 GND PVCC 3 9 GND PGOOD 4 8 VIN 5 6 7 VIN AGND SW 9A 14 BOOT 8A EN 7A SS UQFN-13JL 2x3 (FC) EN SW SW 12A RLIM UQFN-14L 2x3 (FC) 16 15 14 13 SW PVCC 3 10 SW RT 4 9 BOOT 5 6 7 8 PGOOD SW 11 GND 12 2 SS 1 FB VIN AGND Adj. f SW from 300kHz to 700kHz Adj. current limit from 10A to 15A UQFN-16JL 3x3 (FC) SG002-00 OCT 2015 © 2015 Richtek Technology Corporation 5 Selection Guide VIN range up to 23.0V, IOUT up to 8A in WDFN, UQFN packages Key features: 500kHz, Power Goodand±1% VREF accuracy. Vin Current rating Package Over current behaviour Latch-off RDSON P/N Hiccup PSM/PWM Force-PWM For enhanced light load efficiency 4A PGOOD VBYP VIN EN FB 1 2 3 10 9 PGND 5V-23V 4 5 8 7 6 11 SW SW SW BOOT VCC ✓ ✓ 67mΩ/41mΩ RT6219A RT6219BL 67mΩ/41mΩ RT6219AH RT6219BH 31mΩ/20mΩ RT6220A RT6220BL 31mΩ/20mΩ RT6220AH RT6220BH RDSON P/N WDFN-10L 3x3 ✓ AGND EN FB VCC BOOT 6A 14 13 12 11 10 VIN 1 PGND 2 15 9 SW 8 SW SW 16 SW 4 5 6 ✓ 7 VBYP PGOOD AGND AGND VOUT 3 UQFN-16L 3x3 (FC) VIN Current rating Package Over current behaviour With LDO Buck VOUT PSM/PWM For enhanced light load EN2 efficiency 5V-23V 8A 7 6 5 8 VIN 9 GND 70mA, 3.35VLDO Fixed 3.3V 27mΩ/10mΩ RT7238B 70mA, 5.1VLDO Fixed 5.0V RT7238C 70mA, Adj. VLDO, Adj. VOUT 0.6V– 5.0V RT7238D 4 3 2 10 1 LX BOOT LDO VOUT NC PGOOD EN1 Cycle-by-cycle Current limit LDO RT7238B UQFN-10L 3x3 (FC) 7 6 5 8 VIN 9 GND 4 3 2 10 1 LX BOOT NC VOUT NC PGOOD EN BYP RT7238C/E UQFN-10L 3x3 (FC) 7 6 5 8 VIN 9 GND 4 3 2 1 10 LX BOOT LDO FB ILMT PGOOD EN RT7238D UQFN-10L 3x3 (FC) Technical Support ACOT™ Video ACOT™ video Youtube Richtek Designer Application Note SOT-23 FCOL Thermal considerations ACOT™ Stability Testing Comparing Buck converter topologies Choosing the optimal Buck converter for your application ACOT Stability Design Tool ACOT™ video Tudou: ENGLISH,CHINESE ACOT™ video YouKu: ENGLISH,CHINESE SG002-00 OCT 2015 © 2015 Richtek Technology Corporation 6