13/33

L6919E

Figure 6. Constant Current operation

In this particular situation, the switching frequency results reduced. The ON time is the maximum allowed

age with respect to the load value, it can be simply considered that, for example, to have on OCP threshold

Integrated Droop Function

The device uses a droop function to satisfy the requirements of high performance microprocessors, reducing

the size and the cost of the output capacitor.

This method "recovers" part of the drop due to the output capacitor ESR in the load transient, introducing a de-

pendence of the output voltage on the load current

As shown in figure 7, the ESR drop is present in any case, but using the droop function the total deviation of the

tional to the output current. Since the device has an average current mode regulation, the information about the

total current delivered is used to implement the Droop Function.

FB and COMP has always a capacitor in series (See fig. 8). The voltage regulated is then equal to:

given by:

a) Maximum current for each phase

b) Output Characteristic

TonMAX

TonMAX

Ipeak

Vout

Iout

µA)

µA)

UVP

Droop effect

T

OFF

L

Ipe ak

I

OC P x

–

V

OUT

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

⋅

=

f

1

T

ON m a x

T

OFF

+

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

=

V

OUT

VID

R

FB

R

SENSE

Rg

---------------------- I

OUT

⋅⋅

–

=