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
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Constant Frequency
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MLCC Suitable
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Frequency Locked Loop (FLL) provides constant average frequency over line & load.
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Pulse Shaping Regulators (PSR™) supports MLCC-only operation with lowest component count.
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Ultrafast Transient Response
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T-on control with ‘’instant on’’ response provides ultrafast transient response.
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Comparison Table of Richtek Buck Topologies
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Topology
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Current Mode
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CMCOT
Current Mode
Constant-On-Time
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ACOT
Advanced
Constant-On-Time
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Response to Load Steps
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moderate
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fast
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extremely fast
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Current Sense
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current sense limits min. ON time
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low side current sense
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not required
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Min. ON Time
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larger, limits the min. achievable duty-cycle
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small min. On time allows small duty-cycles
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small min. On time allows small duty-cycles
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Frequency
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stable fixed fSW
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constant average fSW
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constant average fSW
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Stable with MLCC
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√
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√
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√
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Slope Compensation
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√
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not required
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not required
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Synchronized to ext. Clock
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√
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x
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x
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Applications
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used for applications with steady load conditions.
(some CM buck converters can be synchronized to an external clock)
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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)
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applications with severe fast load transients , such as DDR, Core SoC, FPGA and ASIC supplies
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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’’.
Example of ACOT® Product Overview: RT7275 &
RT7276
3A, 4.5V to 18V VIN, 700kHzACOT®
Synchronous Step-Down Converter
Datasheet RT7275/RT7276&tab=doc">
RT7275/76 datasheet download (PDF, 356KB)RT7275/RT7276&tab=order">
Features
- 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
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Simplified Application Circuit
Pin Configurations
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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
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VIN
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Current rating
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Package
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fSW
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Over current
behaviour
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IQ
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P/N
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PSM/PWM
For enhanced light load efficiency
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Force-PWM
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2.5V-6.0V
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2A
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1.5MHz
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Cycle-by-cycle
Current limit
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22µA
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RT5784A*Coming soon
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RT5784B*Coming soon
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RT5785A*Coming soon
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RT5785B*Coming soon
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2.5V-5.5V
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2.7MHz
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30µA
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RT5795A
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-
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- 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 fSW and ±1.5% VREF
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VIN
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Current rating
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Package
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Over current behaviour
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P/N
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Hiccup
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Constant current
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PSM/PWM
For enhanced light load efficiency
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Force-PWM
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4.3V-18V
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1.5A
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✓
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RT7255A
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✓
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RT7255B
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✓
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RT7255C
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✓
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RT7255D
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4.5V-18V
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2A
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✓
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RT6232A
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RT6232B
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2.5A
(3Apeak)
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✓
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RT6233A
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RT6233B
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3A
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✓
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RT6234A*Coming soon
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RT6234B*Coming soon
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4.3V-18V
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1.5A
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✓
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RT7285/A
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✓
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RT7285B
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✓
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RT7285C
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✓
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RT7285D
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4.5V-18V
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1.5A
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✓
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RT6211A
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✓
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RT6211B
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4.3V-18V
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2.5A
(3A peak)
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✓
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RT7294A
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✓
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RT7294B
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✓
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RT7294C
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✓
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RT7294D
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4.5V-18V
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2A
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✓
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RT6212A
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✓
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RT6212B
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2.5A
(3A peak)
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✓
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RT6213A
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✓
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RT6213B
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4.3V-18V
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3A
(3.5A peak)
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✓
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RT7295A
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✓
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RT7295B
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✓
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RT7295C
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✓
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RT7295D
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4.5V-18V
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3A
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✓
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RT6214A
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✓
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RT6214B
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