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L6711

17 SYSTEM CONTROL LOOP COMPENSATION

The control loop is composed by the Current Sharing control loop and the Average Current Mode control

loop. Each loop gives, with a proper gain, the correction to the PWM in order to minimize the error in its

regulation: the Current Sharing control loop equalize the currents in the inductors while the Average Cur-

rent Mode control loop fixes the output voltage equal to the reference programmed by VID. Figure 22

shows the block diagram of the system control loop.

Figure 22. Main Control Loop Diagram

The system can be modeled with an equivalent single phase converter which only difference is the equiv-

alent inductor L/3 (where each phase has an L inductor).The ACM control loop gain results (obtained

opening the loop after the COMP pin):

0

500

1000

1500

2000

2500

3000

100

300

500

700

900

Switching Frequency [kHz] per Phase

0

500

1000

1500

2000

2500

3000

100

300

500

700

900

Switching Frequency [kHz] per Phase

COMP

VID

FB

4/5

ERROR AMPLIFIER

PWM3

PWM1

CURRENT

SHARING

DUTY CYCLE

CORRECTION

Co

Ro

L3

L1

PWM2

L2

1/5

1/5

1/5