RY8310

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30V 1.2A 1.4MHz Synchronous Step-Down Regulator

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Where LLIM_AVG is the average start-up current during the soft-start period, and TSS is the soft- start time.

On the other hand, special attention should be paid when selecting these components. The DC bias of these

capacitors can result in a capacitance value that falls below the minimum value given in the recommended capacitor

specifications table.

The ceramic capacitor’s actual capacitance can vary with temperature. The capacitor type X7R, which operates over

a temperature range of −55°C to +125°C, will only vary the capacitance to within ±15%. The capacitor type X5R

has a similar tolerance over a reduced temperature range of −55°C to +85°C. Many large value ceramic capacitors,

larger than 1uF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more

than 50% as the temperature varies from 25°C to 85°C. Therefore, X5R or X7R is recommended over Z5U and

Y5V in applications where the ambient temperature will change significantly above or below 25°C.

Feed-Forward Capacitor (CFF)

RY8310 has internal loop compensation, so adding CFF is optional. Specifically, for specific applications, if

necessary, consider whether to add feed-forward capacitors according to the situation.

The use of a feed-forward capacitor (CFF) in the feedback network is to improve the transient response or higher

phase margin. For optimizing the feed-forward capacitor, knowing the cross frequency is the first thing. The cross

frequency (or the converter bandwidth) can be determined by using a network analyzer. When getting the cross

frequency with no feed-forward capacitor identified, the value of feed-forward capacitor (CFF) can be calculated

with the following Equation:

������������������������������������= 1

2�������������������������������������������������������������������������������������1������������1�1������������1+1������������2�

Where FCROSS is the cross frequency.

To reduce transient ripple, the feed-forward capacitor value can be increased to push the cross frequency to higher

region. Although this can improve transient response, it also decreases phase margin and cause more ringing. In the

other hand, if more phase margin is desired, the feed-forward capacitor value can be decreased to push the cross

frequency to lower region.