R4 (Rapid Robust Ripple) modulation technology provides a compensation-free control loop that eliminates external compensation resistors and capacitors.

The R4 control loop is a unique analog control loop based on a hysteretic current mode, the simplest control topology. It makes control loop decisions using an internally generated synthetic current signal. As a result, the loop is inherently stable with optional, digitally adjustable gain.

Unlike other methods of regulation, R4 has both variable frequency and variable duty cycle. This level of flexibility reduces load step deviation by up to 67% and peak-to-peak deviation by up to 46%.

R4’s superior control loop significantly reduces output voltage variation, resulting in less output capacitance. There’s no overshoot or undershoot, just increased efficiency and decreased BOM and board size.

Key Features

  • Exceptionally high control loop bandwidth
  • Inherently stable architecture
  • Ability to adjust switching frequency and duty cycle in response to a transient load
  • Seamless PFM to PWM transition

Comparison: R4 vs. Voltage Mode vs. Constant On Time (COT)

We compared these three controllers using an external transient load generator (12A Step @ ~25A/µµs) under identical testing conditions:

  • Vin = 12V
  • Vout = 1.0V
  • Switching frequency = 500kHz
  • Lout = 220nH, DCR = 0.25mOhm
  • Cout = 220µF x4, ESR = 4m/cap (ceramic MLCC caps)

Voltage Mode Control Loop

In response to load transients, voltage mode control has variable duty cycle but fixed frequency. That fixed frequency, combined with the voltage mode’s lower bandwidth, causes delays, which increase Vout deviation.

Voltage Mode Control Loop Diagram
Voltage Mode Control Loop Graph

Constant On Time (COT) Loop

COT has the inverse qualities of voltage mode: its frequency is variable but its duty cycle is fixed. The variable frequency helps modulate the load step, load release and peak-peak deviations, but there are still undershoots and overshoots to contend with.

Constant On Time Loop
Constant On Time Graph

R4 Control Loop

By combining variable frequency with variable duty cycle, the R4 control loop is able to respond instantly to load transients, minimizing Vout deviation.

R4 Control Loop
R4 Control Loop Graph

This innovative technology gives your designs much greater stability and efficiency, and its internally generated synthetic current signal minimizes the space used and the number of components required.

Control Loop Load Step Deviation Load Release Deviation Pk-Pk Deviation Over/Undershoot Transient Response
Voltage Mode -44mV +43mV 87mV Yes Fixed Freq.
Variable Duty
COT -38mV +38mV 76mV Yes Variable Freq.
Fixed Duty
R4 -14mV +33mV 47mV No Variable Freq.
Variable Duty

See Also: R5™ Modulation Technology | R3™ Technology