LM2648 datasheet(21/23 Pages) NSC

Part #	LM2648

Description	Two-Phase, Synchronous Step-Down 3-Channel Switching Regulator Controller

PDF	23 Pages

Scroll/Zoom	100%

Manufacturer	NSC [National Semiconductor (TI)]

Direct Link	http://www.national.com

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21 / 23 page

Component Selection (Continued)

Channel 1 and 2

Because the loop characteristics for channels 1 and 2 do not

change with loading, the compensation network is somewhat

more straightforward than for channel 3. As shown in Figure

8, the control-output transfer function consists of one double

pole and one zero.

Therefore, three poles and two zeros are required from the

compensation network. The resulting output-control transfer

function is shown in Figure 9

The power stage double pole and zero frequencies are given

by the following equations:

Double Pole:

Zero:

The voltage mode compensation network is shown below.

The compensation network creates the first pole at 0Hz. The

other poles and zeros can be calculated by the following

equations:

Pole2:

Pole3: (if C

c1 >> Cc2)

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FIGURE 7. Ch.3 Compensation Network

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FIGURE 8. Control-Output Transfer Function

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FIGURE 9. Output-Control Transfer Function

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FIGURE 10. Ch. 1 and 2 Compensation Network

LM2648 Datasheet(PDF) 21 Page - National Semiconductor (TI)