L6722

7 Output voltage positioning

19/34

Time constant matching between the inductor (L / DCR) and the current reading filter

(

) is required to implement a real equivalent output impedance of the system so

avoiding over and/or under shoot of the output voltage as a consequence of a load transient. In

fact, considering the scheme reported on Figure 9, it is possible to observe that:

By applying the time constant matching concept, it results:

=>

then given by (Offset disabled):

The whole power supply can be then represented by a "real" voltage generator with an

Warning:

Droop function is operational for output voltages up to 1.8V.

Caution:

Droop function is optional, in case it is not desired, the Current Sense circuit can be tricked so

that the device always read a null current. To do this, it is enough connecting CS+ directly to the

output voltage leaving CS- unconnected. The reaction will keep CS+ and CS- at the same

voltage, always reading a null current and also assuring the FB disconnection protection to be

effective. To aovid setting the FB-disconnection protection, it is also suggested to connect CS+

To disable also the FB disconnection protection, CS+ can be directly connected to VSEN or

SGND.

Figure 9.

Droop function current reading network

R

PH

C

PH

⋅

S

I

OUT

3

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

1s

L

⋅

DCR

⁄

+

1s

R

⋅

PH

C

⋅

PH

3

⁄

+

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

DC

R

D

--------

⋅⋅

=

L

DCR

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

R

PH

C

⋅

PH

3

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

=

I

CS

I

OUT

3

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

DCR

R

D

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

⋅

=

OUT

VID

R

FB

I

DROOP

⋅

–

VID

R

FB

DCR

R

D

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

I

OUT

⋅⋅

–

VID

R

LL

I

OU

⋅

–

==

=

R

FB

R

LL

R

D

DCR

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

⋅

=

L2

L1

L3

DCR1

DCR2

DCR3

PHASE3

PHASE2

PHASE1

CS+

CS-

FB

x 3

COMP

L2

L1

L3

DCR1

DCR2

DCR3

PHASE3

PHASE2

PHASE1

CS+

CS-

FB

x 3

COMP

Droop Function Enabled

Droop Function Disabled