HC55130IMZ datasheet(17/36 Pages) RENESAS

17 / 36 page

HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150

FN4659 Rev 13.00

Page 17 of 36

June 1, 2006

example RD is calculated to be 41.6k (500/12mA). The

next closest standard value is 41.2k



The true value of ISH-, for the selected value of RD is given

by Equation 8:

For the example above, ISH- equals 7.28mA (500 x 0.6/

41.2K). Verify that the value of ISH- is above the suspected

line leakage of the application. The UniSLIC family will

provide a constant on hook voltage level for leakage currents

up to this value of line leakage.

The ROH resistor, which

is used to set the offhook

overhead voltage, is

calculated using

Equations 9 and 10.

IOH is defined as the

difference between the

ILOOP(min) and ISH-.

Substituting Equation 8

for ISH- into Equation 9 and solving for ROH defines ROH in

terms of ILOOP(min) and RD.

Equation 10 can be used to determine the actual ISH- value

resulting from the RD resistor selected. The value of RD

should be the next standard value that is lower than that

calculated. This will insure meeting the ILOOP(min)

requirement. ROH for the above example equals 39.1k



The current limit is set by a single resistor and is calculated

using Equation 11.

The maximum loop

resistance is calculated

using Equation 12. The

resistance of the

protection resistors

(2RP) is subtracted out

to obtain the maximum

loop length to meet the

required off hook

overhead voltage. If RLOOP(MAX) meets the loop length

requirements you are done. If the loop length needs to be

longer, then consider adjusting one of the following: 1) the

SHD threshold, 2) minimum loop current requirement or 3)

the on and off hook signal levels.

SLIC in the Active Mode

Figure 17 shows a simplified AC transmission model. Circuit

analysis yields the following design equations:

Substitute Equation 14 into Equation 15

Substitute Equation 16 into Equation 17

Substitute Equation 18 into Equation 19

Substituting -VTR/ZL into Equation 20 for IM and rearranging

to solve for VTR results in Equation 21

where:

VRX = The input voltage at the VRX pin.

VA = An internal node voltage that is a function of the loop

current detector and the impedance matching networks.

IX = Internal current in the SLIC that is the difference

between the input receive current and the feedback current.

IM = The AC metallic current.

RP = A protection resistor (typical 30).

ZT = An external resistor/network for matching the line

impedance.

VTX´= The tip to ring voltage at the output pins of the SLIC.

RD =

500

ISHD

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

(EQ. 7)

ISH- =

500

---------- (0.6)

(EQ. 8)

VBH

VSAT

VOH(off)

2.5V

OFF HOOK

LOOP CURRENT

ILOOP(min)

DC FEED CURVE

ISH-

IOH

OVER HEAD

ROH

500

IOH

----------

500

ILOOP(min)- ISH-

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

(EQ. 9)

ROH =

RD500

RDILOOP(min)- 500(.6)

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

(EQ. 10)

RLIM =

1000

ILOOP(max)

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

(EQ. 11)

VBH

VSAT

VOH(off)

2.5V

LOOP CURRENT

ILOOP(min)

DC FEED CURVE

RLOO

P(MA

RLOOP(max) =

VBH VSAT 2V VOH off





–

ILOOP(min)

------------------------------------------------------------------------------- -2RP

(EQ. 12)

VA = IM 2RS

80k

---------- 200



ZTR 2RP

–





(EQ. 13)

------- ZTR 2RP

–



(EQ. 14)

VRX

500k

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

500k

------------- = IX

Node Equation

(EQ. 15)

VRX

500k

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

IM ZTR 2RP

–



1000k

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

(EQ. 16)

IX500k - VTX + IX500k = 0

Loop Equation

(EQ. 17)

VTX

2VRX IM ZTR 2RP

–



–

(EQ. 18)

VTR-IM2RP + VTX = 0

Loop Equation

(EQ. 19)

VTR

IMZTR 2VRX

–

(EQ. 20)

VTR 1

ZTR

-----------







– VRX

(EQ. 21)

HC55130IMZ Datasheet(PDF) 17 Page - Renesas Technology Corp

HC55130IMZ Datasheet(HTML) 17 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

Datasheet Download

Link URL