L6712AD datasheet(21/29 Pages) STMICROELECTRONICS

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L6712A L6712

Where

∆IREAD is the difference between one phase current and the ideal current (IMAX/2).

For RSENSE = 4mΩ and IMAX = 40A the current sharing error is equal to 2.5%, neglecting errors due to Rg

and RSENSE mismatches.

3.12.2Average Current Mode (ACM) Control Loop (DROOP=FB)

The average current mode control loop is reported in Figure 18. The current information IDROOP sourced by

the DROOP 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;

■ ZP(s) is the impedance resulting by the parallel of the output capacitor (and its ESR) and the applied

load Ro;

■ ZF(s) is the compensation network impedance;

■ ZL(s) is the parallel of the two inductor impedance;

■ A(s) is the error amplifier gain;

■

is the ACM PWM transfer function where

∆VOSC is the oscillator ramp amplitude

and has a typical value of 3V

■ RA_Gain is the Remote Amplifier Gain.

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

loop gain results:

Considering now that in the application of interest it can be assumed that Ro>>RL; ESR<<Ro and

RDROOP<<Ro, it results:

LOOP s

()

PWM Z

F s

() R

DROOP

RA_Gain Z

⋅

P s

()

⋅

P s

() Z

L s

()

F s

()

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

()

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

⎝⎠

⎛⎞

⋅

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

–

DROOP

Rsense

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

⋅

PWM

---

∆V

OSC

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

⋅

LOOP s

()

---

∆V

OSC

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

F s

()

P s

() Z

L s

()

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

--------

RA_Gain Z

⋅

P s

()

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

⎝⎠

⎜⎟

⎛⎞

⋅⋅

⋅

–

LOOP s

()

---

∆V

OSC

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

F s

()

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

1s Co

DROOP

RA_Gain

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

ESR

⎝⎠

⎛⎞

⋅

---

2Ro

⋅

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

Co ESR

2Ro

⋅

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

⋅

------------------------------------------------------------------------------------------------------------------------------------------- RA_Gain

⋅⋅

⋅

–

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