ISL6277HRZ datasheet(30/37 Pages) RENESAS

30 / 37 page

ISL6277

FN8270 Rev 1.00

Page 30 of 37

Mar 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

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 23 thru 25 give the

VCn(s) expression.

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

Current-sensing resistor Rsen value does 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 17 and Figures 22, 26 and 28;

resistor Ri sets the droop current, Idroop. Tables 1 and 2 show the

internal OCP threshold. It is recommended to design Idroop

without using the Rcomp resistor.

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.

Idroop is designed to be 45μA at full load, so the OCP trip level is

1.25x of the full load current.

For inductor DCR sensing, Equation 26 gives the DC relationship

of Vcn(s) and Io(s):

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:

where Iomax is the full load current and 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 = 65A and Idroopmax = 45μA. Equation 29

gives Ri = 359Ω.

For resistor sensing, Equation 30 gives the DC relationship of

Vcn(s) and Io(s).

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:

where Iomax is the full load current and Idroopmax is the

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

Rsen =1mΩ, Iomax = 65A and Idroopmax = 45µA, Equation 33

gives Ri = 481Ω.

FIGURE 28. RESISTOR CURRENT-SENSING NETWORK

RSUM

DCR

RSUM

PHASE2 PHASE3

DCR

PHASE1

RSUM

ISUM+

ISUM-

VCN

RSEN

VCn s



Rsen

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





ARsen





(EQ. 23)

ARsen s





sns

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

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

(EQ. 24)



Rsen

Rsum

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



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

(EQ. 25)

VCn

Rntcnet

Rsum

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

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

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











(EQ. 26)

Idroop

-----

Rntcnet

Rsum

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

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

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



(EQ. 27)

Rntcnet DCR



NRntcnet

Rsum

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







Idroop



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

(EQ. 28)

Rntcs Rntc

 R



Rntcs Rntc Rp

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



Iomax



Rntcs Rntc

 R



Rntcs Rntc Rp

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

Rsum

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









Idroopmax



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

(EQ. 29)

VCn

Rsen

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



(EQ. 30)

Idroop

-----

Rsen

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



(EQ. 31)

Rsen Io



NIdroop



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

(EQ. 32)

Rsen Iomax



NIdroopmax



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

(EQ. 33)

ISL6277HRZ датащи(PDF) 30 Page - Renesas Technology Corp

ISL6277HRZ датащи(HTML) 30 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

датащи скачать

ссылки URL