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Step-Down (Buck) Converters

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Richtek Buck Product Family

  • Current Mode Buck converters

  • CMCOT Buck converters

  • ACOT product family

    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 components or external ripple injection scheme. The ACOT family includes latch-off, hiccup and constant current protection modes. Richtek has introduced the whole range of ACOT Buck converters up to 12A output current capacity and the input range is from 4.5V to 23V. The ACOT Buck converters are ideal for Set Top Boxes, industrial and commercial low power systems, computer peripherals and LCD Monitors and TVs. See the list of ACOT products.
  • Wide Input Voltage Range DC-DC power solutions for industrial, Automotive and LED lighting applications

    Richtek offers comprehensive power conversion solutions for input voltages ranging up to 60V, suitable for a wide range of applications in the industrial, automotive, and professional lighting field. The key features for Buck converter parts in wide input range are: Robust control architectures for coping with noisy environments, PGOOD and adjustable Soft-start for power sequencing, thermally enhanced packages for operation in higher ambient temperatures, and fully stable with all ceramic input and output capacitors for extended operation life time. We also offer products qualified over -40°C to 85°C industrial temperature range as well as automotive AEC-Q100 standard qualified parts. See the list of selected products.



The following is a list of products released in the last

Part NumberDescriptionShareDatasheetFree Sample
RT5753A/RT5753B3A, 1.2MHz, 5.5V Synchronous Step-Down Converter In WDFN-8L 2x2 Not available
RT5751A/RT5751B6V 1A, ACOT® Buck Converter Not available
RT5761A/RT5761B6V 1A, ACOT® Buck Converter in Thin UDFN-6L 1.4x1 Package Not available
RT5750A/RT5750B6V 1A, ACOT® Buck Converter Not available
RT62306A, 23V, 500kHz, ACOT® Synchronous Buck Converter Not available
RT6262A/RT6262B17V Input, 2A, ACOT® Buck Converter with Both FETs OC Protection Not available
RT6274C/RT6274D18V Input, 3.5A, ACOT® Buck Converter with Both FETs OC Protection Not available
RT5760A/RT5760B/RT5760C/RT5760D6V 1A, ACOT® Buck Converter in Thin SOT-563 Package Not available
RT62855A, 30V, 500kHz Asynchronous Step-Down Converter Not available
RT6258BH/RT6258CH8A, 23V Synchronous Step-Down Converter with 3.3V/5V LDO Not available
RT6263A/RT6263B17V Input, 3A, ACOT® Buck Converter with Both FETs OC Protection Not available
RTQ634542VIN, 5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RTQ634342VIN, 3.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT6272A/RT6272B17V Input, 2A, ACOT® Buck Converter with Both FETs OC Protection Not available
RT6273A/RT6273B17V Input, 3A, ACOT® Buck Converter with Both FETs OC Protection Not available
RT6256BH/RT6256CH6A, 23V Synchronous Step-Down Converter with 3.3V/5V LDO Not available
RTQ636560VIN, 5A, Asynchronous Step-Down Converter with Low Quiescent Current Request
RT58002.1MHz, 3 CHs, Step-Down Converter with I2C Interface Not available
RTQ636060VIN, 0.5A, Asynchronous Step-Down Converter with Low Quiescent Current Request
RTQ634042VIN, 0.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RTQ636160VIN, 1.5A, Asynchronous Step-Down Converter with Low Quiescent Current Request
RTQ634242VIN, 2.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RTQ636360VIN, 3.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RTQ636260VIN, 2.5A, Asynchronous Step-Down Converter with Low Quiescent Current Request
RT6283B3A, 30V, 500kHz Synchronous Step-Down Converter Not available
RT634342VIN, 3.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT6306A6A, 23V Synchronous Step-Down Converter Not available
RT80991.5MHz, 600mA, High Efficiency PWM Step-Down Converter Not available
RT634542VIN, 5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT6308A8A, 23V Synchronous Step-Down Converter Not available
RTQ2823A/RTQ2823B8A, 17V, High Efficiency Synchronous Step-Down Converter Not available
RT636360VIN, 3.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT636560VIN, 5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT636160VIN, 1.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT636060VIN, 0.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT634242VIN, 2.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT634042VIN, 0.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT636260VIN, 2.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RTQ28166A, 18V, Synchronous Step-Down Converter Not available
RT634142VIN, 1.5A, Asynchronous Step-Down Converter with Low Quiescent Current Not available
RT6253A/RT6253B17V Input, 3A, ACOT® Buck Converter with Both FETs OC Protection Not available
RT6252A/RT6252B17V Input, 2A, ACOTTM Buck Converter with Both FETs OC Protection Not available
RT6264A/RT6264B18V Input, 4A, ACOTTM Buck Converter with Both FETs OC Protection Not available
RT6258D8A, 23V Synchronous Step-Down Converter with 5V LDO Not available
RT6260C10A, 23V Synchronous Step-Down Converter with 5V LDO Not available
RTQ2822A/RTQ2822B12A, 17V, High Efficiency Synchronous Step-Down Converter Not available
RT6203E6A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter with VID Control Not available
RT6243A/RT6243B12A, 17V, High Efficiency Synchronous Step-Down Converter Not available
RT6203F6A, 18V, 700kHz ACOTTM Synchronous Step-Down Converter with VID Control Not available
RTQ2105-QA36VIN, 3A, High Efficiency Synchronous Step-Down Converter with Low Quiescent Current Not available
RTQ2104-QA36VIN, 3A, High Efficiency, 2.1MHz, Synchronous Step-Down Converter with Low Quiescent Current Request
RTQ2106-QA36VIN, 3A, High Efficiency, 2.1MHz, Synchronous Step-Down Converter with Low Quiescent Current Not available
RT6215F2A, 24V, 800kHz, ACOT® Step-Down Converter Not available
RT57599A, 6.5V, 1MHz, ACOT® Synchronous Step-Down Converter with I2C Interface Not available
RTQ2132B-QT1.2A, 36V, 2.1MHz Synchronous Step-Down Converter Request

Buck converter definition

Buck converters are switch-mode step-down converters which can provide high efficiency and high flexibility at higher VIN/VOUT ratios and higher load current.

Most Buck converters contain an internal high side MOSFET and synchronous rectifier MOSFET, which are in turn switched on and off via internal duty-cycle control circuit to regulate the average output voltage. The switching waveform is filtered via an external LC filter stage.

Buck converter features

Due to the fact that the MOSFETs are either ON or OFF, Buck converters dissipate very little power, and the duty-cycle control makes large VIN/VOUT ratios possible. The internal MOSFETs RDS(ON) mainly determines the current handling capabilities of the Buck converter, and the MOSFET voltage ratings determine the maximum input voltage. The switching frequency together with the external LC filter components will determine the ripple voltage on the output. Higher switching frequency buck converters can use smaller filter components, but switch losses will increase. Buck converters with Pulse Skipping Mode (PSM) will reduce their switching frequency at light load, thereby increasing light load efficiency, which can be important in applications with low power standby modes.

The Richtek DC/DC portfolio contains a wide range of Buck converters with different control topologies, including Current Mode (CM), Current Mode-Constant On Time (CMCOT) and Advanced Constant On Time (ACOT™) control topologies. Each topology is suitable for different applications and requirements. For example, Richtek unique ACOT™ family has extremely fast transient response compared to CM and CMCOT topologies, which makes it ideal for applications that exhibit very fast load transients, such as DDR, Core SoC, FPGA and ASIC supplies.

Comparison Table of Richtek Buck Topologies

Key features CM
Current Mode
CMCOT
Current Mode
Constant-On-Time
ACOT™
Advanced
Constant-On-Time
Topology BuckConverter BuckConverter BuckConverter
Steady-state &
Step load
BuckConverter BuckConverter BuckConverter
VIN/IOUT range
  • 2.5Vin to 5.5Vin / up to 6A for low Vin and battery-powered applications
  • Up to 36Vin / up to 10A
  • Up to 60Vin for Industrial and 36Vin for Automotive applications
  • 2.5Vin to 5.5Vin / up to 3A
  • Up to 23Vin / up to 12A
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 fSW constant average fSW constant average fSW
Stable with MLCC
Slope Compensation not required not required
Synchronized to ext. Clock X X
Richtek Designer™ simulation tool Create your account and get your designs up and running in no time. (partial parts have been released) Coming soon Create your account and get your designs up and running in no time. (partial parts have been released)
Applications For applications with steady load conditions. Also for industrial and automotive applications. For 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)
For applications with severe fast load transients , such as DDR, Core SoC, FPGA and ASIC supplies

Buck Converter Selection Criteria

In order to select a suitable Buck converter for your application, some key criteria are important to be considered.


Application input voltage

Which upper bound of input voltage fits for your application best?
Richtek Buck converters can be divided into 3 main groups to fulfill different application requirements. Richtek LV Buck converters are suitable for running off single cell Li-Ion batteries as well as supplies from 5V rails. The 18V rated HV Buck converters are often used for applications that run from 12V. We also provide parts up to 36V input range for industrial supplies or automotive applications with large input voltage fluctuation.


Application current consumption

How to calculate the power loss and maximum application peak current?
When considering the Buck converter current rating, there are two factors to consider: The application average current consumption and the application peak current.
  • The application average current will determine the average heat in switching MOSFETs which is related to conduction losses and switching losses. Conduction losses are related to the internal MOSFET RDS(ON) : The MOSFET conduction losses are I2 * RDS(ON) ; Switching losses are mostly related to the current, the input voltage and the switching frequency. In most standard applications, the switching losses are roughly 30% of the total losses, but in applications with higher input voltage or high frequency, the switching losses can increase considerably. The application total power losses can be derived from the datasheet efficiency curve: BuckConverter .
  • The device maximum rated current and over-current protection level must be considered when checking application peak load current. The difference between load current and inductor peak or valley current is ½ the inductor ripple current, so be sure to include this when checking the application maximum load current in relation to OCP current levels.


Light load efficiency

When to select Force-PWM mode or PSM mode?
For supply rails that need to be active in low power standby modes, it is desirable to make the Buck converter efficiency at light load as high as possible. Force-PWM Buck converters keep the switching frequency fixed over the entire load range while Pulse Skip Mode (PSM) will reduce switching frequency at light load, thereby improving light load efficiency since the majority of losses at light load are caused by switching loss. Read more for PSM operation principle and its advantages and drawbacks.


Switching frequency

How to select suitable switching frequency?
Higher switching frequency makes it possible to use smaller inductor and capacitors, and improves the step load behaviour of the converter. However, it also increases switching losses and extends the EMI radiation frequency range. Higher switching frequency can also limit the maximum step-down ratio that can be achieved : The minimum duty-cycle is limited by the converter minimum ON time and the frequency: BuckConverter , so BuckConverter
In general, higher VIN applications should use lower switching frequency devices.

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Low BOM cost

How to reduce BOM cost?
Choosing the right Buck topology together with the most optimal IC package can bring you cost savings on both passive components and IC cost. ACOT™ topology offers superior load transient response, making it possible to reduce the size of your output capacitors and still meet the load transient voltage undershoot requirement. Flip-Chip in TSOT-23-6 package offers lowest package cost, while maintaining good thermal performance and low RDS(ON) due to the absence of bonding wire