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.
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.