19/33

L6919E

necessary) to sense the current. The current sharing error is internally dominated by the voltage offset of Tran

conductance differential amplifier; considering a voltage offset equal to 2mV across the sense resistor, the cur-

rent reading error is given by the following equation:

Where

Rsense mismatches.

Figure 14. Current Sharing Control Loop

Average Current Mode (ACM) Control Loop

pin flows into RFB implementing the dependence of the output voltage from the read current.

The ACM control loop gain results (obtained opening the loop after the COMP pin):

Where:

–

is the equivalent output resistance determined by the droop function;

load Ro;

– A(s) is the error amplifier gain;

–

· is the ACM PWM transfer function where

and has a typical value of 3V

Removing the dependence from the Error Amplifier gain, so assuming this gain high enough, the control loop

gain results:

I

RE AD

∆

I

MAX

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

2m V

R

SENSE

I

MAX

⋅

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

=

L1

L2

+

+

PWM1

1/5

1/5

PWM2

COMP

CURRENT

SHARING

DUTY CYCLE

CORRECTION

D02IN1393

G

()

PWM Z

() R

DROOP

Z

()

+

()

⋅

⋅

Z

() Z

()

+

()

Z

()

As

()

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

1

1

As

()

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

+



 R

FB

⋅

+

⋅

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

=

R

DROOP

R

sense

R

g

------------------- R

FB

⋅

=

PWM

4

5

---

V

IN

∆

V

OSC

∆

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

⋅

=