L6918 L6918A

16/35

Figure 6. Constant Current operation

It can be observed that the peak current (Ipeak) is greater than the 140% but it can be determined as follow:

The device works in Constant-Current, and the output voltage decreases as the load increase, until the output

off, the FAULT pin is driven high and the device stops working. Cycle the power supply to restart operation. The

maximum average current during the Constant-Current behavior results:

In this particular situation, the switching frequency results reduced.

the load value, it can be simply considered that, for example, to have on OCP threshold of 170%, this will cor-

INTEGRATED DROOP FUNCTION

The devices use the 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

output voltage is minimized. In practice the droop function introduces a static error proportional to the output

rent mode regulation, the information about the total current delivered is used to implement the Droop Function.

and Vout, the total current information flows only in this resistor because the compensation network between

TonMAX

TonMAX

Ipeak

Vout

Iout

µA)

MAX,TO

UVP

Droop effect

Ipeak

I

OC Px

V

IN

Vout

min

–

L

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

Ton

MAX

I

OC Px

V

IN

Vout

MIN

–

L

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

0.5 T

⋅⋅

+

=

⋅

+

=

I

MA X T OT

,

2I

MAX

2I

OC Px

Ipeak

I

OC P x

–

2

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

+





⋅

=

⋅

=

f

1

Ton

MAX

T

OF F

+

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

=

T

OF F

L

Ipea k

I

OC Px

–

V

OU T

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

⋅

=