AN-158 Datasheet, PDF (4/10 Pages) IXYS Corporation – LITELINK™ III Application Circuit Calculations

Application Note: AN-158
2. LITELINK III DC Characteristic Equations
The following equations describe the dc operating
characteristics of the telephone line side of LITELINK
III and LITELINK III dc requirements for the loop.
2.1 Loop Current Limit
R_ZDC, R_ZTX, and R_ZNT determine the off-hook loop
current.
I_CL =
----¹----^V----
R_ZDC
+ -_R----_Z---⁰_T----_X^.--⁶---_|²--_|--⁵-_R---^V-_Z----_NT + 5.5mA
Adjust the value of R_ZDC to modify the loop current
limit characteristics.
2.2 Minimum Line Operating Current
The portion of the LITELINK on the telephone line side
of the internal optical barrier is powered from the
phone line, and requires a minimum operating current
from the phone line to work. This value is calculated
as follows:
I _MIN = _R-----_Z---⁰_T----_X^.-⁶----²_|--_|--⁵-_R---^V-_Z----_NT + 5.5mA
2.3 DC Line Current Versus Line Voltage Characteristics
2.3.1 Minimum Loop Voltage
The minimum loop voltage with which LITELINK III will
operate is defined as:
V _LINE ≥ V _BRIDGE + V _PEAK + 3.25V
where V_PEAK is the peak value of the signal on the
line.
Note: R_DCS3 is not needed in circuits where ratio
constraint described above is met. R_DCS3 is not used
in IXYS Integrated Circuits Division application circuits
where the error introduced is negligible.
2.3.2 Line Current Programming Resistor
Ratio Requirement
LITELINK III requires the following circuit ratio for
operation:
(^---R^-----_D^----_C^----_S^-R---₂^{-D---+-C----S-}R^---1-_D^-|_C^{-| -R}_S^-₁^D--C||^-SR^-3-_D^-_C^--_S^-₃)
≈
---¹----
1.2
Failure to meet this requirement will result in poor error
cancellation within LITELINK III.
AN-158-R03
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