ISL6277

30

FN8270.1

March 8, 2012

Resistor Current-Sensing Network

Figure 28 shows the resistor current-sensing network for a

3-phase solution. Each inductor has a series current sensing

form a filter for noise attenuation. Equations 23 thru 25 give the

variation over-temperature, so there is no need for the NTC

network.

Overcurrent Protection

Refer to Equation 1 on page 17 and Figures 22, 26 and 28;

For example, the OCP threshold is 1.5V on the IMON pin. This

translates to 45μA of ISUM current or 56.25μA of droop current.

1.25x of the full load current.

For inductor DCR sensing, Equation 26 gives the DC relationship

Substitution of Equation 26 into Equation 1 gives Equation 27:

Therefore:

Substitution of Equation 18 and application of the OCP condition

in Equation 28 gives Equation 29:

corresponding droop current. For example, given N = 3,

For resistor sensing, Equation 30 gives the DC relationship of

Substitution of Equation 30 into Equation 1 gives Equation 31:

Therefore:

Substitution of Equation 32 and application of the OCP condition

in Equation 28 gives Equation 33:

corresponding droop current. For example, given N = 3,

FIGURE 28. RESISTOR CURRENT-SENSING NETWORK

CN

DCR

L

DCR

L

PHASE2 PHASE3

DCR

L

PHASE1

RI

VCN

RSEN

RSEN

RSEN

+

-

V



R

sen

N

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

I





A

Rsen



s



=

(EQ. 23)

A



1

1

s



sns

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

+

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

=

(EQ. 24)



Rsen

1

R

sum

N

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

C

n



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

=

(EQ. 25)

V

Cn

R

ntcnet

R

ntcnet

R

sum

N

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

+

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

DCR

N

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













I

o



=

(EQ. 26)

I

droop

1

R

i

-----

R

ntcnet

R

ntcnet

R

sum

N

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

+

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

DCR

N

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





I

o



=

(EQ. 27)

R

i

R

ntcnet

DCR



I

o



NR

ntcnet

R

sum

N

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

+







I

droop



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

=

(EQ. 28)

R

i

R

ntcs

R

ntc

+

 R

p



R

ntcs

R

ntc

R

p

++

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

DCR



I

omax



N

R

ntcs

R

ntc

+

 R

p



R

ntcs

R

ntc

R

p

++

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

R

sum

N

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

+









I

droopmax



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

=

(EQ. 29)

V

Cn

R

sen

N

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

I

o



=

(EQ. 30)

I

droop

1

R

i

-----

R

sen

N

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

I

o





=

(EQ. 31)

R

i

R

sen

I

o



NI

droop



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

=

(EQ. 32)

R

i

R

sen

I

omax



NI

droopmax



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

=

(EQ. 33)