ISL95839 datasheet(24/36 Pages) RENESAS

Part #	ISL95839

Description	Dual 31 PWM Controller with Current Monitor for IMVP-7/VR12??CPUs

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Manufacturer	RENESAS [Renesas Technology Corp]

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24 / 36 page

ISL95839

FN8315 Rev 0.00

Page 24 of 36

May 9, 2013

current, idroop may have sharp spikes, which may adversely

affect idroop average value detection and therefore may affect

OCP accuracy. User discretion is advised.

Resistor Current-Sensing Network

Figure 23 shows the resistor current-sensing network for a

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

resistor Rsen. Rsum and Ro are connected to the Rsen pads to

accurately capture the inductor current information. The Rsum

and Ro resistors are connected to capacitor Cn. Rsum and Cn

form a filter for noise attenuation. Equations 24 thru 26 give

VCn(s) expression:

Transfer function ARsen(s) always has unity gain at DC.

Current-sensing resistor Rsen value will not have significant

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

network.

The recommended values are Rsum = 1kΩ and Cn = 5600pF.

Overcurrent Protection

Refer to Equation 1 on page 16 and Figures 17, 21 and 23;

resistor Ri sets the droop current Idroop. Tables 2 and 3 show the

internal OCP threshold. It is recommended to design Idroop

without using the RCOMP resistor.

For example, the OCP threshold is 60µA for 3-phase solution. We

will design Idroop to be 50µA at full load, so the OCP trip level is

1.2x of the full load current.

For inductor DCR sensing, Equation 27 gives the DC relationship

of Vcn(s) and Io(s).

Substitution of Equation 27 into Equation 1 gives Equation 28:

Therefore:

Substitution of Equation 19 and application of the OCP condition

in Equation 29 gives Equation 30:

where Iomax is the full load current, Idroopmax is the

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

Rsum = 3.65kΩ, Rp = 11kΩ, Rntcs = 2.61kΩ, Rntc = 10kΩ,

DCR = 0.9mΩ, Iomax = 94A and Idroopmax = 50µA, Equation 30

gives Ri = 467Ω.

For resistor sensing, Equation 31 gives the DC relationship of

Vcn(s) and Io(s).

Substitution of Equation 31 into Equation 1 gives Equation 32:

Therefore:

Substitution of Equation 33 and application of the OCP condition

in Equation 29 gives Equation 34:

where Iomax is the full load current, Idroopmax is the

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

Rsen =1mΩ, Iomax = 94A and Idroopmax = 50µA, Equation 34

gives Ri = 627Ω.

Load Line Slope

Refer to Figure 10.

For inductor DCR sensing, substitution of Equation 28 into

Equation 2 gives the load line slope expression:

FIGURE 23. RESISTOR CURRENT-SENSING NETWORK

Cn

Rsum

Ro

DCR

L

DCR

L

Rsum

Ro

Phase2

Phase3

Io

DCR

L

Phase1

Ro

Rsum

Ri

ISUM+

ISUM-

Vcn

Rsen

VCn s



Rsen

N

------------- Io s





ARsen



s



=

(EQ. 24)

ARsen s



1

s



Rsen

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

+

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

=

(EQ. 25)



Rsen

1

Rsum

N

--------------- Cn



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

=

(EQ. 26)

VCn

Rntcnet

Rsum

N

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

+

------------------------------------------ DCR

N

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









Io



=

(EQ. 27)

Idroop

1

Ri

-----

Rntcnet

Rsum

N

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

+

------------------------------------------ DCR

N

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



Io



=

(EQ. 28)

Ri

Rntcnet DCR



Io



NRntcnet

Rsum

N

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

+







Idroop



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

=

(EQ. 29)

Ri

Rntcs Rntc

+

 R

p



Rntcs Rntc Rp

++

---------------------------------------------------- DCR



Iomax



N

Rntcs Rntc

+

 R

p



Rntcs Rntc Rp

++

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

Rsum

N

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

+









Idroopmax



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

=

(EQ. 30)

VCn

Rsen

N

------------- Io



=

(EQ. 31)

Idroop

1

Ri

-----

Rsen

N

------------- Io



=

(EQ. 32)

Ri

Rsen Io



NIdroop



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

=

(EQ. 33)

Ri

Rsen Iomax



NIdroopmax



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

=

(EQ. 34)

LL

Vdroop

Io

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

Rdroop

Ri

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

Rntcnet

Rsum

N

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

+

------------------------------------------ DCR

N

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



==

(EQ. 35)

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