ADIN1111BCPZ-R7 datasheet(24/109 Pages) AD

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Data Sheet

ADIN1111

ON-CHIP DIAGNOSTICS

analog.com

Rev. A | 24 of 109

Fault Detection with the TDR Engine

The Analog Devices algorithm has a time resolution of 8.3 ns,

which translates to a length resolution of less than 1 m and a

maximum of 1600 m, with an accuracy of 2%.

This fault detector algorithm is capable of finding open and short

fault conditions even when the ADIN1111 is physically connected

to another PHY through their MDI, which implies that the link

partner PHY is potentially transmitting DME pages. Traditional TDR

methods struggle to find faults if other signal sources or noise is

also present in the same link. This is not the case of the Analog

Devices solution, which makes it suitable for debugging when there

is no control over the remote end.

The fault detector algorithm is provided as a C-code library con-

taining the high-level functions required for diagnostics. These func-

tions have been optimized to not utilize any advanced processing

so that they can be executed by any low-power microcontroller.

A single function call is sufficient to execute the fault detector. The

function returns the type of fault and the distance to the fault in

meters from the MDI connector.

The fault detect TDR library can be requested from the software

section in the landing page of the ADIN1100, ADIN1110, and

ADIN2111.

TDR Offset Calibration

The library includes a function to calibrate the offset of the TDR

measurement. This particular function in the library is useful given

that different MDI circuits may introduce variable delays in the

signal path, which can contribute to the offset of the length meas-

urement. For instance, an isolation transformer on the MDI is highly

likely to introduce a signal delay that corresponds to a couple of

meters in length.

This calibration is not required to run the fault detector, and an

average value is provided by default. However, it is recommended

for short cables if accuracy is required. If this calibration is required,

it can be done once in the lab for a specific MDI circuit implementa-

tion, and the offset value can then be stored in nonvolatile memory

for future use.

To perform this calibration, the MDI port must be left open or

shorted. No load or cable can be connected to the MDI port.

Cable Calibration

By default, the algorithm is optimized to support long reach cables

compliant with the IEEE 802.3cg standard. However, given the

wide variety of cable types, which have different insertion loss,

return loss, and signal delay characteristics, the library includes

a calibration function that optimizes the algorithm to operate with

any cable, and estimates its nominal velocity of propagation (NVP)

for more accurate length estimations. The length accuracy mainly

depends on the accuracy of the NVP value.

To run this calibration, a cable with a known length must be attach-

ed to the MDI port, and its end must be left open or shorted. NVP

values are generally between 0.5 and 0.9 and are a property of

the construction of the cable. In general, an average NVP value of

approximately 0.65 can be assumed. This calibration is not required

to run the fault detector, unless higher length accuracy is needed

or if nonstandard cables are utilized. This calibration can be done

once in the laboratory for a given cable, and the values can be

stored in nonvolatile memory.

Refer to the C-code driver for more information related to the usage

of these functions.

Length/Distance to Fault Accuracy

The accuracy of the distance to a fault, or length measurements,

mainly depends on the NVP value, which is determined by the

accuracy of the cable length used to perform the NVP calibration.

Table 20 provides results for induced faults and distance-to-fault

measurements for different cables and lengths. In all cases, the al-

gorithm was successful finding the open or short conditions induced

during the test. The NVP value for the Profibus PA cable used in

this test was roughly estimated, and the same was used for the

Cat5E and Cat6 cables.

Table 20. Length Estimation Error for Different Cables

Cable Type

Estimated

Length (m)

Length

Error (%) Note

Fieldbus Type A - AWG 18

50.2

0.7

NVP calibrated

Fieldbus Type A - AWG 18

102.1

2.1

NVP calibrated

Fieldbus Type A - AWG 18

403.4

0.8

NVP calibrated

Fieldbus Type A - AWG 18

807.6

0.8

NVP calibrated

Fieldbus Type A - AWG 18

1045.3

1.0

NVP calibrated

Fieldbus Type A - AWG 18

1462.9

2.0

NVP calibrated

Cat5E

133.1

2.4

NVP not calibrated

Cat5E

244.4

1.8

NVP not calibrated

Cat6

73.6

5.1

NVP not calibrated

Cat6

137.2

5.6

NVP not calibrated

LINK QUALITY MONITORING

The ADIN1100, ADIN1101, ADIN1110, ADIN1111, and ADIN2111

provide the mean squared error (MSE) measurement of the re-

ceived signal, which directly relates to the signal-to-noise ratio

(SNR) seen by the PHY receiver. The MSE or SNR can be mapped

to a signal quality indicator (SQI) and can be used for assessing the

overall 10BASE-T1L link segment/channel quality.

The link quality may be affected by the cable length, the cable

properties such as insertion and return loss, presence, quality and

connection of the cable shield, number and quality of possible

interconnections between cable segments, as well as level of noise

in the environment around the devices and the cable. Therefore,

the link quality can provide useful information during a device

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