L6758ATR datasheet(24/42 Pages) STMICROELECTRONICS

24 / 42 page

Output voltage positioning

L6758A

24/42

DocID023298 Rev 2

The Iout register contains analog-to-digital conversion of the voltage present on the IMON

pin considering the following relationships:

MON

⋅

IMON ,

where R

IMON

is the resistor connected between IMON and

GND.

IMON=1.24 V corresponds to IMAX. R

IMON

is designed according to this

relationship.

IMON=1.55 V sets the OC protection.

6.5

Single-phase section: current reading

The single-phase section performs the same differential current reading across DCR as the

multi-phase section. According to

Section 6.2, the current that flows from the SCSN pin is

then given by the following equation (see

Figure 6):

Equation 6

6.6

Single-phase section: defining load-line

This method introduces a dependence of the output voltage on the load current recovering

part of the drop due to the output capacitor ESR in the load transient. Introducing a

dependence of the output voltage on the load current, a static error, proportional to the

output current, causes the output voltage to vary according to the sensed current.

Figure 6 shows the current sense circuit used to implement the load-line. The current

flowing across the inductor DCR is read through R

. R

programs a trans-conductance

gain and generates a current I

SDROOP

proportional to the current delivered by the single-

phase section that is then sourced from the SFB pin. R

SFB

gives the final gain to program

the desired load-line slope (

Figure 5).

The output characteristic vs. load current is then given by:

Equation 7

where R

SLL

is the resulting load-line resistance implemented by the single-phase section.

The R

SFB

resistor can be then designed according to the R

SLL

as follows:

Equation 8

SCSN

DCR

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

SO U T

⋅

S DRO OP

SO U T

=V I D

SFB

SD RO O P

⋅

–

VID

SFB

DC R

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

SO U T

⋅⋅

–

VID

SL L

SO UT

⋅

–

SFB

SLL

DC R

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

⋅

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