ADIN1110CCPZ-R7 datasheet(25/107 Pages) AD

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Data Sheet

ADIN1110

ON-CHIP DIAGNOSTICS

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Rev. B | 25 of 107

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 19 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 19. 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

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