ROHM’s New QuiCur Technology Improves Load Transient Responses for DC/DC Converter ICs and LDOs
QuiCur, announced March 24, heralds improvements in both response speed and in voltage output stability.
Power unit designers employ power supply ICs to monitor a unit’s output voltage on a moment-by-moment basis. The ICs utilize a feedback loop to fine-tune the output voltage by comparing it to an internal reference voltage. This is illustrated in the top half of the diagram directly below:
Controlling a power source's output. Image used courtesy of ROHM
There is a basic trade-off in this critical aspect of power supply design. It is crucial to revert the output voltage to its correct value as quickly as possible; But the rub is that moving too fast can destabilize the circuit and cause it to oscillate. This is further complicated by the fact that response speed is also influenced by output capacitance.
Enter ROHM’s QuiCur technology.
QuiCur’s dedicated error amp prevents the feedback circuit from entering an unstable frequency area. The amp’s second stage, as illustrated above, allows for current drive adjustment of the gain. Though the critical zero-cross frequency can vary as a function of the connected output capacitance, through gain adjustment it can then be set at the upper limit of the stable control regions.
With the two error amps sharing roles, this innovation is applicable across the gamut of power supply ICs that incorporate feedback circuits.
Reducing Capacitors and Saving Board Space
One of the key properties of QuiCur technology is its ability to quickly respond to fluctuations in response to output load current. This minimizes the output capacitance required by the power supply IC, and as a result reduces the required number of external components.
QuiCur reduces capacitor requirements, saving board space. Image used courtesy of ROHM
Compared to conventional products offered by ROHM and others, equivalent response performance can be achieved with less than half the capacitance. That translates directly to less required board space and a lower final product BOM.
Stable Operation in the Face of Specifications Change
An increase in the output capacitance will cause the output voltage to become more stable. However, the cost of that increase is a deterioration in the instantaneous response performance, also known as the “time to react.”
QuiCur enables linear adjustment (negative constant proportional) of both the output capacitance and output voltage fluctuation, since the instantaneous response performance won’t change even in the face of output capacitance increase. Thus, stable operation is achieved and output fluctuations are reduced.
Combining QuiCur with ROHM’s Nano Cap
Nano Cap, another of ROHM’s technologies, provides stable power output control through improvement response in analog circuits, while simultaneously minimizing associated parasitic factors. Per ROHM, this allows the output capacitance “to be reduced to less than 1/10th that of present conventional solutions.”
At that level, one need not utilize a capacitor at the regulator’s output. Instead, stable operation can be produced with just a 100 nF capacitor at the MCU side, saving yet more board space.
So, while QuiCur itself can reduce the output capacitance to the order of microfarads, Nano Cap makes it possible to hit nanofarads.
ROHM is working to bring QuiCur-enabled power ICs to market, with plans to ship DC/DC converter IC samples in April and LDO ICs in July.