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The RT2855A/B are high-performance 650kHz 4A step-down regulators with internal power switches and synchronous rectifiers. They feature quick transient response using their Advanced Constant On-Time (ACOT®) control architecture that provides stable operation with small ceramic output capacitors and without complicated external compensation, among other benefits. The input voltage range is from 4.5V to 18V and the output is adjustable from 0.765V to 7V.

The proprietary ACOT® control improves upon other fast-response constant on-time architectures, achieving nearly constant switching frequency over line, load, and output voltage ranges. Since there is no internal clock, response to transients is nearly instantaneous and inductor current can ramp quickly to maintain output regulation without large bulk output capacitance. The RT2855A/B are stable with and optimized for ceramic output capacitors.

With internal 70mΩ switches and 30mΩ synchronous rectifiers, the RT2855A/B display excellent efficiency and good behavior across a range of applications, especially for low output voltages and low duty cycles. Cycle-by-cycle current limit, input under-voltage lock-out, externally-adjustable soft-start, output under- and over-voltage protection, and thermal shutdown provide safe and smooth operation in all operating conditions.

The RT2855A and RT2855B are each available in
WQFN-16L 3x3 package, with exposed thermal pads. The RT2855B switches continuously even at light loads to avoid low-frequency interference while the RT2855A features a power-saving discontinuous operating mode at light loads.

Applications

  • Industrial and Commercial Low Power Systems
  • Computer Peripherals
  • LCD Monitors and TVs
  • Green Electronics/Appliances
  • Point of Load Regulation for High-Performance DSPs, FPGAs, and ASICs
Key Spec.
RT2855A RT2855B
Status Active Active
Vin (min) (V) 4.5 4.5
Vin (max) (V) 18 18
Number of Outputs 1 1
Vout (min) (V) 0.765 0.765
Vout (max) (V) 7 7
Output Adj. Method Resistor Resistor
Iout (max) (A) 4 4
Current Limit (typ) (A) 6 6
Freq (typ) (kHz) 650 650
Ext Sync No No
Ron_HS (typ) (mOhm) 70 70
Ron_LS (typ) (mOhm) 30 30
Iq (typ) (mA) 1 1
Features ACOT Control;Adjustable Soft-Start;COT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;OCP;OTP;OVP;PSM;Power Good;SCP;Stable with Ceramic Capacitor;UVP ACOT Control;Adjustable Soft-Start;COT Control;Cycle-by-Cycle Current Limit;Enable Input;Fast Transient Response;Force PWM;OCP;OTP;OVP;Power Good;SCP;Stable with Ceramic Capacitor;UVP
Package Type WQFN3x3-16 WQFN3x3-16
Features
  • Fast Transient Response
  • Steady 650kHz Switching Frequency at all Load Current (RT2855B)
  • Discontinuous operating mode at Light Load (RT2855A)
  • 4A Output Current
  • Advanced Constant On-Time (ACOT®) Control
  • Optimized for Ceramic Output Capacitors
  • 4.5V to 18V Input Voltage Range
  • Internal 70mΩ Switch and 30mΩ Synchronous Rectifier
  • 0.765V to 7V Adjustable Output Voltage
  • Externally-adjustable, Pre-biased Compatible Soft-Start
  • Cycle-by-Cycle Current Limit
  • Optional Output Discharge Function
  • Output Over- and Under-voltage Shut-down
    ► Latched (RT2855ALGQW/RT2855BLGQW Only)
    ► Hiccup Mode (RT2855AHGQW/RT2855BHGQW Only)
  • Input Under Voltage Lockout
  • Thermal Shutdown
Datasheet
TitleLast UpdateDownload
4A, 18V, 650kHz, ACOT® Synchronous Step-Down Converter2015/04/29
Part NumberPackage TypePackage Qty.Free SampleBuy From Authorized Distributor
RT2855ALGQWWQFN3x3-161500 Request Buy from Distributor
RT2855BHGQWWQFN3x3-161500 Request Buy from Distributor
RT2855BLGQWWQFN3x3-161500 Request Buy from Distributor
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