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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

MLCC Suitable


Frequency Locked Loop (FLL) provides constant average frequency over line & load.

Pulse Shaping Regulators (PSR™) supports MLCC-only operation with lowest component count.


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Ultrafast Transient Response




T-on control with ‘’instant on’’ response provides ultrafast transient response.



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Comparison Table of Richtek Buck Topologies

Topology

Current Mode

CMCOT
Current Mode
Constant-On-Time

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 fSW

constant average fSW

constant average fSW

Stable with MLCC

Slope Compensation

not required

not required

Synchronized to ext. Clock

x

x

Applications

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



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">/2013www/images/pdficon.gifRT7275/76 datasheet download (PDF, 356KB)RT7275/RT7276&tab=order">/2013www/images/bt_fsb.gif

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

Simplified Application Circuit

Adobe Systems

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

VIN

Current rating

Package

fSW

Over current

behaviour

IQ

P/N

PSM/PWM

For enhanced light load efficiency

Force-PWM

2.5V-6.0V

2A

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1.5MHz

Cycle-by-cycle
Current limit

22µA

RT5784A*Coming soon

RT5784B*Coming soon

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RT5785A*Coming soon

RT5785B*Coming soon

2.5V-5.5V

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2.7MHz

30µA

RT5795A

-


  • 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

VIN

Current rating

Package

Over current behaviour

P/N

Hiccup

Constant current

PSM/PWM

For enhanced light load efficiency

Force-PWM

4.3V-18V

1.5A

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RT7255A



RT7255B




RT7255C



RT7255D

4.5V-18V

2A

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RT6232A

RT6232B

2.5A

(3Apeak)


RT6233A

RT6233B

3A


RT6234A*Coming soon

RT6234B*Coming soon

4.3V-18V

1.5A

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RT7285/A



RT7285B




RT7285C



RT7285D

4.5V-18V

1.5A

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RT6211A




RT6211B

4.3V-18V

2.5A

(3A peak)

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RT7294A



RT7294B




RT7294C



RT7294D

4.5V-18V

2A

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RT6212A




RT6212B

2.5A

(3A peak)


RT6213A




RT6213B

4.3V-18V

3A

(3.5A peak)

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RT7295A



RT7295B




RT7295C



RT7295D

4.5V-18V

3A

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RT6214A




RT6214B


  • 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 fSW and ±1% VREF

VIN

Current rating

Package

Features

Over current behaviour

P/N

Power

Good

VOUT

Discharge

function

Latch-off

Hiccup

Constant current

PSM/PWM

For enhanced light load efficiency

Force-PWM

4.5V-18V

2A

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RT7280GCP

RT7279GCP

3A



RT7276GCP

RT7275GCP

4A



RT7232GCP

RT7231GCP

5A



RT7236GCP

RT7235GCP

2A

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RT7280GQW

RT7279GQW

3A




RT7276GQW

RT7275GQW

4A




RT7232GQW

RT7231GQW

5A




RT7236GQW

RT7235GQW

5.5A




RT6206BHGQW

RT6206AHGQW

2A

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RT7274GSP

RT7281GSP

3A





RT7278GSP

RT7277GSP

4A





RT7234GSP

RT7233GSP

4A





RT6201AHGSP

RT6201BHGSP

5A





RT7240GSP

RT7239GSP

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

fSW

Over current behaviour

RON

P/N

PSM/PWM

For enhanced light load efficiency

Force-PWM

4.5V-18V

5A

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650kHz

Cycle-by-cycle

Current limit

60m/22m

RT6207A

RT6207B

6A

51m/18m

RT6236A

RT6236B

7A

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500kHz

40m/16m

RT6237A

RT6237B

8A

35m/14m

RT6238A

RT6238B

9A

30m/12m

RT6239A

RT6239B

12A

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Adj. fSW from 300kHz
to
700kHz

Adj. current limit from
10A to 15A

12m/5.4m

RT6242A

RT6242B


  • 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

RDSON

P/N

Latch-off

Hiccup

PSM/PWM

For enhanced light load efficiency

Force-PWM


5V-23V

4A

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67mΩ/41mΩ

RT6219A

RT6219BL



67mΩ/41mΩ

RT6219AH

RT6219BH


6A

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31mΩ/20mΩ

RT6220A

RT6220BL



31mΩ/20mΩ

RT6220AH

RT6220BH




VIN

Current rating

Package

Over current behaviour

With LDO

Buck

VOUT

RDSON

P/N

PSM/PWM

For enhanced light load efficiency

5V-23V

8A

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Cycle-by-cycle

Current limit

70mA, 3.35VLDO

Fixed
3.3V

27mΩ/10mΩ

RT7238B

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70mA,

5.1VLDO

Fixed
5.0V

RT7238C

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70mA,

Adj. VLDO,

Adj. VOUT

0.6V– 5.0V

RT7238D



Technical Support


ACOT™ Video

ACOT™ video Youtube

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ACOT™ video Youtube: ENGLISH,CHINESE

ACOT™ video YouKu: ENGLISH,CHINESE

Richtek Designer

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Application Note


Related Parts
TitlePart NoDocument
2A, 5.5V, Low IQ ACOT Synchronous Step-Down Converter RT5795A
18V, 1.5A, 500kHz ACOTTM Step-down Converter in 8 Pin TSOT-23 RT7255
2A, 18V, 500kHz, ACOT™ Step-Down Converter RT6232ART6232B
3A Peak, 18V, 500kHz, ACOT™ Step-Down Converter RT6233ART6233B
1.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7285RT7285A
1.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7285B
1.5A, 18V, 500kHz, ACOT™ Step-Down Converter RT6211ART6211B
2.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7294A
2.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7294B
2A, 18V, 500kHz, ACOT™ Step-Down Converter RT6212ART6212B
3A Peak, 18V, 500kHz, ACOTTM Step-Down Converter RT6213ART6213B
3.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7295A
3.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7295B
18V, 3A, ACOTTM Step-Down Converter in 6 and 8 Pin TSOT-23 RT6214ART6214B
2A, 18V, 700kHz ACOT™ Synchronous Step-Down Converter RT7274RT7279RT7280RT7281
3A, 18V, 700kHz ACOT™ Synchronous Step-Down Converter RT7275RT7276
4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT7231RT7232RT7233RT7234
5A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT7235RT7236RT7239RT7240
5.5A, 18V, 650kHz, ACOTTM Synchronous Step-Down Converter RT6206B
3A, 18V, 700kHz ACOT™ Synchronous Step-Down Converter RT7278
4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6201ART6201B
5A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6202ART6202B
5A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6207ART6207B
6A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6236ART6236B
7A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter RT6237ART6237B
8A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter RT6238ART6238B
9A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter RT6239ART6239B
12A, 18V, 500kHz, ACOT™ Synchronous Step-Down Converter RT6242ART6242B
4A, 23V, 500kHz, ACOTTM Synchronous Buck Converter RT6219
6A, 23V, 500kHz, ACOTTM Synchronous Buck Converter RT6220
8A, 23V, 500kHz Synchronous Step-Down Converter with 3.3V/5V LDO RT7238BRT7238CRT7238DRT7238E
1.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7285C
1.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7285D
2.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7294C
2.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7294D
3.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7295C
3.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT7295D
5.5A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6206A
3A, 18V, 700kHz ACOT™ Synchronous Step-Down Converter RT7277
3A, 18V, 500kHz, ACOT™ Step-Down Converter RT6234ART6234B
12A, 23V, 500kHz, ACOT™ Synchronous Buck Converter with VTT LDO for Memory Power Supply RT7241A
3A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT6259ART6259B
2.5A, 24V, 800kHz, ACOT™ Step-Down Converter RT6216F
2.5A, 24V, 500kHz, ACOT™ Step-Down Converter RT6216E
24V, 3A, 800kHz, ACOTTM Step-Down Converter in 8 Pin TSOT-23 RT6217F
2A, 6V, 1.5MHz, 25μA IQ, ACOT™ Synchronous Step-Down Converter RT5785ART5785B
24V, 3A, 500kHz, ACOTTM Step-Down Converter in 8 Pin TSOT-23 RT6217E
2A, 6V, 1.5MHz, 25μA IQ, ACOT™ Synchronous Step-Down Converter RT5784ART5784B
2A, 18V, 1.4MHz ACOT™ Synchronous Step-Down Converter RT6222CRT6222D
2.5A, 18V, 500kHz ACOT™ Synchronous Step-Down Converter RT6222ART6222B
10A, 18V, 500kHz, ACOTTM Synchronous Step-Down Converter RT2810ART2810B
6A, 23V, 500kHz, ACOTTM Synchronous Buck Converter with LDO for System 5V RT7291ART7291B
6A, 23V, 500kHz, ACOTTM Synchronous Buck Converter with LDO for System 3.3V RT7290A
4A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT2855ART2855B
5A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT7240A
3A, 18V, 650kHz ACOT™ Synchronous Step-Down Converter RT2858B
3A, 18V, 650kHz, ACOT™ Synchronous Step-Down Converter RT2853ART2853B
3A, 18V, 700kHz ACOT™ Synchronous Step-Down Converter RT7266
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