19/27

L6712A L6712

worst case is the response time after removal of the load with the minimum output voltage programmed

and the maximum input voltage available.

MAIN CONTROL LOOP

The system control loop topology depends on the DROOP pin connection: if connected to FB (droop func-

tion active) an Average Current Mode topology must be considered while, if connected to GND (droop

function not active) a Voltage Mode topology must be considered instead.

Anyway, the system control loop encloses the Current Sharing control loop to allow proper sharing to the

inductor' currents. Each loop gives, with a proper gain, the correction to the PWMs in order to minimize

the error in its regulation: the Current Sharing control loop equalize the currents in the inductors while the

output voltage control loop fixes the output voltage equal to the reference programmed by VID (with or

without the droop effect and with or without considering the Remote Amplifier Gain). Figure 12 reports the

block diagram of the main control loop.

Figure 12. Main Control Loop Diagram

Current Sharing (CS) Control Loop

Active current sharing is implemented using the information from Trans conductance differential amplifier.

read current and this reference is converted to a voltage with a proper gain and it is used to adjust the duty

cycle whose dominant value is set by the error amplifier at COMP pin (See fig. 13).

The current sharing control is a high bandwidth control loop allowing current sharing even during load transients.

The current sharing error is affected by the choice of external components; choose precise Rg resistor

(±1% is necessary) to sense the current. The current sharing error is internally dominated by the voltage

offset of Trans conductance differential amplifier; considering a voltage offset equal to 2mV across the

sense resistor, the current reading error is given by the following equation:

L1

L2

+

+

PWM1

1/5

+

-

1/5

4/5

PWM2

FB

COMP

ERROR

AMPLIFIER

REFERENCE

PROGRAMMED

BY VID

CURRENT

SHARING

DUTY CYCLE

CORRECTION

D03IN1518

RA_Gain

READ

I

MAX

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

2mV

R

⋅

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

=