Novel feedback loop reduces dc-dc output capacitance s


Branded QuiCur, the technique is intended to reduce the amount of capacitance needed at the supply’s output, while navigating the balance between fast loop response for good load and line fluctuation response, and the instability caused if the loop is too quick.

It uses a two-part error amplifier (right), with a filter followed by an amplifier whose gain can be adjusted on-the-fly.

According to the company, it does two things:

Allows the 0dB cross-over frequency to be pushed higher (through the area labelled as ‘unusable’ in the top part of the diagram below). Electronics Weekly has asked Rohm for more detail here.

Rohm QuiCur graph

And the variable gain amplifier can be set to stabilise the 0dB cross-over frequency in the face of different values of output capacitor.

“Although the zero-cross frequency may vary depending on the connected output capacitance, by adjusting the amplification factor, the zero-cross frequency can always be set at the limit” (blue-pink boundary line in lower diagram left).

A set of demonstration dc-dc converters producing a 1V output from a 5V input (below) were subject to a 0A to 2A step in 2μs.

Rohm evample converter

A conventional loop with a 100kHz 0dB cross-over and the four 22μF capacitors shown resulted in a 30mV output dip (below).

Turning on the new loop with only a single 22μF output capacitors fitted and 300kHz 0dB cross-over achieved almost the same performance: a 40mV dip.

Adding a second 22μF capacitor, totalling 44μF compared with 88μF in the conventional design, dropped the dip to 20mV while and maintained the 300kHz 0dB cross-over, according to Rohm.

Rohm evample converter

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Incorporating the newly developed high-speed load response technology QuiCur™ in power supply ICs makes it possible to achieve the ideal performance without causing instability in feedback circuits. Not only can the number of external components and mounting area be reduced by minimizing the capacitance of the output capacitor required by the power supply IC, but linear adjustment of the capacitance and output voltage fluctuations (negative constant proportional relationship) is enabled, ensuring stable operation even when the capacitance increases due to specification changes. This contributes to a significant reduction in power supply circuit design resources by providing stable operation with fewer external components.

ROHM is currently working to commercialize QuiCur™-equipped power supply ICs, with plans to ship samples of DC/DC converter ICs in April and LDOs in July of this year.
(Fig. 1 + 2)

QuiCur™ Technology’s detail

(Fig. 4 + 5)

Click on the URL below for more information on Nano Cap™.

ROHM Establishes QuiCur: Maximizing the Response Performance of Power Supply ICs

Contributing to reducing power supply circuit design resources by providing stable operation with fewer external components

Willich-Münchheide, Germany, March 24, 2022 –





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