AN273 [SILICON]
GR-909 TESTING WITH THE Si321X PROSLIC㈢; WITH THE Si321X PROSLIC㈢ GR- 909测试
| 型号： | AN273 |
| 厂家： | 
SILICON |
| 描述： | GR-909 TESTING WITH THE Si321X PROSLIC㈢ |
| 文件： | 总8页 (文件大小：214K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AN273
GR-909 TESTING WITH THE Si321X PROSLIC®
1. Introduction
This document describes how line fault testing (such as GR-909) may be implemented using the Si321X family of
ProSLIC devices. Demonstration code for each test is available.
2. GR-909 Metallic Loop Tests
The five metallic loop tests described by GR-909 are as follows:
1. Hazardous Potential Test
Under any condition, the following must be detected
>50 V
ac voltage from TIP-GND or RING-GND
RMS
>135 V dc voltage from TIP-GND or RING-GND
2. Foreign Voltage Test
Under any condition, the following voltages not generated by the SLIC must be detected
>10 V
ac from TIP-GND or RING-GND
RMS
>6 V dc from TIP-GND or RING-GND
3. Resistive Faults Test
Detect the following resistive line faults
<150 kΩ TIP-RING, TIP-GND, or RING-GND
4. Receiver Off-hook Test
Distinguish between resistive fault <150 kΩ and an off-hook receiver
5. Ringing Equivalency Number Test
Determine the REN (Ringer Equivalency Number) of the terminating receiver is between 0.175 REN and
5 REN. Reject if outside that range.
Each of these tests can be implemented on the Si321x devices. Table 1 enumerates the test cases, the measure-
ment method implemented, and the failing criteria.
Table 1. GR-909 Metallic Loop Tests
GR-909 Test
Test Description
Linefeed State
Measurement
Failure Criteria
1
Hazardous Potential
OPEN
V
and V
> 50 Vrms ac
> 135 V dc
TIP
RING
2
Foreign Voltage
OPEN
V
and V
> 10 Vrms ac
> 6 V dc
TIP
RING
3
4
5
Resistive Faults
Offhook
TIP-OPEN, RING-OPEN
TIP-OPEN
R
, R , R
>150 kΩ
Detect/No-detect
> 5 REN
TG RG TR
R
TR
REN
RINGING
PQ2
Rev. 0.1 2/06
Copyright © 2006 by Silicon Laboratories
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3. Tests 1 & 2: Hazardous Potential and Foreign Voltages
These tests employ the same measurement technique; so, they can be implemented as a single test to save time,
assuming that the source of the hazardous potential is always foreign (not generated by the SLIC). The exception
would be if the user implements high-voltage ringing on a short loop, which may result in a ring signal that delivers
>50 V
to the load and/or a dc potential >135 V between ring bursts. The user must be cognizant of this possi-
RMS
bility.
The dc voltage on TIP and RING can be directly read from Direct Registers 80 and 81 while in the OPEN linefeed
state; however, in the presence of a foreign ac voltage, it is very inaccurate. If a large enough sample set is taken
at timed intervals to reconstruct an ac voltage at a minimum of 20 Hz, both the ac and dc voltages are quantified.
If N samples are taken at fixed intervals, the ac and dc voltages on TIP (or RING) may be calculated as follows:
N – 1
1
N
---
VTIP.DC
=
VTIP(n)
∑
n = 0
Equation 1.
N – 1
1
N
2
---
VTIP.AC
=
(VTIP(n) – VTIP.DC)
∑
n = 0
Equation 2.
1.5 V
1.5 V
RST
TIP
RSH*
RSR
RING
*RSH installation is optional
Figure 1. Si321X OPEN Linefeed State DC Equivalent Circuit
Refer to the demonstration code for an example of implementing ac voltage measurement.
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4. Test 3: Resistive Faults
Since the small change in loop or longitudinal currents introduced by high impedance line faults may be too small
to detect with the Si321x current monitoring, the large source impedance of the open terminal in the TIP-OPEN and
RING-OPEN linefeed states can be utilized to force a large voltage change on the open terminal that can easily be
detected. To measure resistive faults to GND (either TIP-GND or RING-GND), it is necessary to install the optional
shunt resistor, RSH, to provide a small loop current reference. When a fault to GND is present on the OPEN termi-
nal, the longitudinal current is altered, and the impedance may be calculated.
If R is not installed, resistive faults between TIP and RING can still be measured. However, faults from TIP-GND
SH
or RING-GND must be detected using a less accurate method, which will only account for gross faults (<30 kΩ).
4.1. Condition 1: No Resistive Fault
If no resistive faults are present, the voltage on the TIP lead while in the TIP-OPEN linefeed state and the voltage
on the RING lead while in the RING-OPEN linefeed state is said to be at the critical voltage. It is necessary to iden-
tify this because if a resistance is to be calculated as a function of the open terminal voltage, there are limiting volt-
age values that result in an infinite resistance calculation. Though an infinite resistance is a valid measurement,
software applications need to avoid making a calculation with an infinite result. By first identifying the voltage in
which there are no line faults present, this calculation can be avoided. An equation for the critical voltage will be
derived in the following sections. In a no-fault loop (see Figure 2), the following equations apply:
VTIP = 1.5 V – RST × ILOOP
V
TIP – VRING
----------------------------------
=
ILOOP
RSH
1.5 × RSH + RST × VRING
------------------------------------------------------------------
=
VTIP
R
ST + RSH
where I
is the quiescent loop current flowing due to the shunt resistor added across TIP and RING; R is the
ST
LOOP
TIP source impedance, and R is the resistor added to create the loop current. Table 2 shows the values for R ,
SH
ST
R
, and R for the applicable linefeed states and BOM options.
SR
SH
1.5 V
RST
TIP
ILOOP
RSH
VOC
RSR
RING
Figure 2. No-Fault TIP-OPEN DC Equivalent Circuit
Rev. 0.1
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Table 2. DC Source Resistances
Resistor
BOM Option
Tip-Open
200 kΩ
340 kΩ
160 Ω
Ring-Open
Open
200 kΩ
340 kΩ
200 kΩ
340 kΩ
680 kΩ
1 MΩ
Standard
High Voltage
Standard
160 Ω
160 Ω
200 kΩ
340 kΩ
680 kΩ
1 MΩ
R
ST
SR
SH
R
R
High Voltage
Standard
160 Ω
680 kΩ
1 MΩ
High Voltage
4.2. Condition 2: TIP to RING Fault
If a resistive fault from TIP to RING (R ) is present (see Figure 3), the loop impedance is reduced; thus, the loop
TR
current, I
, increases, which results in a larger drop across R (TIP source impedance) and a more negative
ST
LOOP
voltage at the TIP terminal that can easily be detected.
From the voltages at TIP and RING, the resistive fault, R , may be calculated from the following equation:
TR
RSH × RST( VRING – VTIP
)
-------------------------------------------------------------------------------------------------------------
=
RTR
RSH(1.5 + VTIP ) – RST( VRING – VTIP
)
Equation 3.
Examining Equation 3, there is a single value for V
in which the denominator is zero and R is infinite. This is
TR
TIP
the critical voltage, V
. Solving the denominator for V , the critical voltage is expressed as follows:
TIP_CRIT
TIP
RST × VRING – 1.5 × RSH
--------------------------------------------------------------------
=
VTIP_CRIT
R
SH + RST
Equation 4.
1.5 V
RST
TIP
RSH
RTR
VOC
RSR
RING
Figure 3. TIP-OPEN Linefeed State with TIP to RING Resistive Fault
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If R is not installed, a resistive fault present between TIP and RING will provide enough loop current to cause the
SH
voltage on the TIP lead to drop. Since all of the loop current passes through the resistive fault, R , the equation
TR
for R becomes as follows:
TR
RST( VRING – VTIP
)
--------------------------------------------------------
=
RTR
1.5 + VTIP
Equation 5.
4.3. Condition 3: TIP to GND Fault
Resistive faults from TIP to GND are also detected in the TIP-OPEN linefeed state. In this case, the resistive fault
from TIP to GND (R ) reduces the longitudinal current through R (see Figure 4); thus, a more positive voltage is
TG
ST
present at the TIP terminal. Equation 6 describes R as a function of the TIP and RING voltages. Note that the
TG
denominator is the same as in the R calculation; so, the same critical voltage applies.
TR
1.5 V
TIP
RST
RSH
RTG
VOC
RSR
RING
Figure 4. TIP-OPEN Linefeed State with TIP to GND Resistive Fault
From the voltages measured at TIP and RING, the resistive fault from TIP to GND may be expressed as follows:
– VTIP × RST × RSH
-------------------------------------------------------------------------------------------------------------
=
RTG
RSH(1.5 + VTIP ) – RST( VRING – VTIP
)
Equation 6.
If R
is not installed, a gross measurement of the impedance from TIP-GND may be made in the FORWARD
SH
ACTIVE linefeed state. By applying a high common-mode voltage to TIP and keeping the differential voltage to 0 V
(V = 0), a resistive fault will form a voltage divider along with the 160 Ω output impedance of the TIP lead in the
OC
FORWARD ACTIVE state (see Figure 5).
Rev. 0.1
5
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If the common mode voltage is high enough and R is low enough, a detectable longitudinal current will result.
TG
VCM
RST
TIP
RTG
VOC + VCM
RSR
RING
Figure 5. Forward Active State with TIP-GND Fault
Since V
is only limited by V , and the minimum detectable longitudinal current is 1.25 mA, the minimum
CM
BAT
detectable fault is as follows:
VBAT
----------------------
1.25 mA
RTG
=
+ RST
Equation 7.
of –74 V, the minimum detectable resistive fault is ~60 kΩ.
For a typical V
BAT
4.4. Condition 4: RING to GND Fault
Resistive faults from RING to GND are also detected in the same manner as the TIP to GND case, except the line-
feed is now in the RING-OPEN state (see Figure 6). As before, the addition of the resistive fault, R , results in an
TG
increased voltage at the RING terminal.
TIP
VOC
RST
RSH
1.5 V
RSR
RING
RRG
Figure 6. RING-OPEN Linefeed State with RING to GND Resistive Fault
From the voltages measured at TIP and RING, the resistive fault from RING to GND may be expressed as:
– VRING × RSR × RSH
------------------------------------------------------------------------------------------------------------------
=
RRG
RSH(1.5 + VRING ) – RSR( VTIP – VRING
)
Equation 8.
If R is not installed, the RING-GND impedance is measured just as the TIP-GND impedance was measured (see
SH
Equation 7).
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Rev. 0.1
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5. Test 4: Receiver Off-Hook Test
GR-909 requires that the SLIC be able to differentiate between an off hook handset and a resistive fault. The dc
impedance presented to the SLIC by a typical telephone varies with applied voltage; therefore, this nonlinearity
may be exploited to determine whether a telephone is present.
By measuring the TIP lead in the TIP-OPEN linefeed state at two V settings, the two dc impedances R (refer
OC
TR
to Equation 3) may be compared. If these two measurements differ by more than ~50% and they are within the
expected range, an off hook telephone may be present. If a resistive fault is present, the variation will be within the
resistance measurement accuracy, typically 10–25%.
This test may be performed with or without R installed. If R is not installed, refer to Equation 5 to calculate
SH
SH
R
.
TR
5.1. Test 5: REN Test
The Si321X can detect relatively small capacitive loads on the line. Line capacitance can be measured by either
measuring the time constant of a decaying voltage on RING when in the OPEN mode (single-slope conversion) or
by detecting longitudinal current when a subthreshold ring signal is applied. From the measured loop capacitance,
the REN load may be estimated to within ± 0.5 REN.
5.1.1. Single-Slope Conversion
After charging the RING lead to V
in the FORWARD ACTIVE linefeed state, if the linefeed state is switched to
RING
the OPEN state, the voltages between the TIP and RING leads will discharge through their series output resistance
(see Figure 1). By measuring the time delay from V = upper threshold to V = lower threshold, the capaci-
RING
RING
tance can be calculated and the REN load estimated. This is ideal for detecting very small REN loads.
Because high REN loads present such a large capacitance and, therefore, very large time constants, it may be
more advantageous to implement a subthreshold ringing method. It is only recommended that the single-slope
method be used for loads less than 0.75 REN.
5.1.2. Subthreshold Ringing Method
The best method for estimating REN load when the load is >0.75 REN is by applying a small amplitude ring signal
to the line and correlating the power dissipated in the linefeed pullup (Q2) to a known REN load. This requires the
user to calibrate his hardware/software to known 1, 3, and 5 REN loads. This calibration determines the slope and
offset of a straight line that correlates the REN load to the Q2 power dissipation. Once calibrated, future measure-
ments utilize curve fitting to estimate the REN load.
Figure 7 shows the relationship between Q2 power dissipation and an applied REN load for a typical Si321X hard-
ware design. By calibrating the hardware and identifying two straight lines, REN can be measured with ~± 0.5 REN
accuracy.
Q2 Power
Best Fit Line
Measured
# REN (applied)
Figure 7. Typical Q2 Power vs. Applied REN Load
Rev. 0.1
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Toll Free: 1+(877) 444-3032
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8
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