LM2648 National Semiconductor, LM2648 Datasheet - Page 21

• Manufacturer Part Number: LM2648
• Description: Synchronous Step-Down 3-Channel Switching Regulator Controller
• Manufacturer: National Semiconductor

Component Selection
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
FIGURE 8. Control-Output Transfer Function
FIGURE 7. Ch.3 Compensation Network
(Continued)
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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
FIGURE 10. Ch. 1 and 2 Compensation Network
FIGURE 9. Output-Control Transfer Function
c1
>>
C
c2
)
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