RT6318B datasheet(19/25 Pages) RICHTEK

19 / 25 page

RT6318B/C

DS6318B/C-01 December 2021

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 5. Bode Plot with Different Feedback Loop Conditions

The transfer function of feedforward network is expressed

in equation (1) and the positions of zero and pole are

calculated in equation (2) and equation (3).

OUT

1 +

V(s)

R1 C

(1)

V(s)

1 +

(R1//R2) C



f =

(2)

(R1//R2) C

 

f =

(3)

2R1 C

 

Observing Figure 5, the maximum phase boost occurs

between zero and pole frequencies that is defined as

maximum phase boost frequency, as expressed in

equation (4). Hence, in order to achieve the maximum

phase boost by adding CFF in the RT6318B/C, the

system's original bandwidth has to be located at maximum

phase boost frequency.

ph_max

= f

(4)



For putting zero at the correct frequency to implement

maximum phase boost, the first thing is to determine

system's bandwidth. There is a simple way to measure

bandwidth of the RT6318B/C that is load transient analysis.

By using a converter without feedforward network to

observe the voltage deviation frequency during load step,

the bandwidth of converter can be obtained because of

the crossover frequency related to voltage deviation

frequency approximately, as shown in Figure 6.

VOUT

IOUT

Figure 6. A Simply Way to Get the Bandwidth

Following the above concept, the equation of bandwidth

with feedforward CFF can be derived, as expressed in

equation (5).

BW =

(5)

R1C













For optimizing transient response, the CFF can be obtained

from equation (5), as shown in equation (6).

(6)

2BW R1











After defining the CFF, please also check the load regulation,

because feedforward capacitor might inject an offset

voltage into VOUT to cause VOUT inaccuracy. If the output

voltage is over spec caused by calculated CFF, please

decrease the value of feedforward capacitor CFF.

Dividing resistors of the RT6318B/C is listed in following

table.

RT6318B 데이터시트(PDF) 19 Page - Richtek Technology Corporation

RT6318B 데이터시트(HTML) 19 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

데이터시트 다운로드

링크 URL