L6714D datasheet(57/70 Pages) STMICROELECTRONICS

57 / 70 page

L6714

System control loop compensation

57/70

System control loop compensation

The control loop is composed by the Current Sharing control loop (See Figure 8) 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 Current 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.

The system Control Loop is reported in Figure 23. The current information IDROOP sourced

by the DROOP pin flows into RFB implementing the dependence of the output voltage from

the read current.

Figure 22. Main control loop

The system can be modeled with an equivalent single phase converter which only difference

is the equivalent inductor L/N (where each phase has an L inductor).The Control Loop gain

results (obtained opening the loop after the COMP pin):

PWM3

PWM2

PWM1

4 / 5

VREF

ERROR AMPLIFIER

COMP

ZF(s)

ZFB(s)

DROOP

IDROOP

COUT

ROUT

1 / 5

CURRENT SHARING

DUTY CYCLE

CORRECTION

IINFO1

IINFO3

IINFO2

PWM4

1 / 5

IINFO4

LOOP s

()

PWM

F s

()

DROOP

P s

()

⋅⋅

P s

() Z

L s

()

[]

F s

()

--------------

()

------------

⎝⎠

⎛⎞

⋅

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