LT4295 datasheet(25/50 Pages) AD

25 / 50 page

LTC9101-1/

LTC9102/LTC9103

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Multipoint Detection

The LTC9101-1/LTC9102/LTC9103 uses a multipoint

method to detect PDs. False-positive detections are min-

imized by checking for signature resistance with both

forced current and forced voltage measurements.

Initially, two test currents are forced onto the channel (via

the OUTn pin) and the resulting voltages are measured.

The detection circuitry subtracts the two V-I points to

determine the resistive slope while removing offset caused

by series diodes or leakage at the port (see Figure 14). If

the forced current detection yields a valid signature resis-

tance, two test voltages are then forced onto the channel

and the resulting currents are measured and subtracted.

Both methods must report valid resistances to report a

valid detection. PD signature resistances between 17k

and 29k (typically) are detected as valid and reported as

Detect Good in the corresponding Port Status register or

Channel Status register, as appropriate. Values outside

this range, including open and short circuits, are also

reported. If the channel measures less than 1V during

any forced current test, the detection cycle will abort and

Short Circuit will be reported. Table 8 and Table 9 show

the possible detection results.

Detection is enabled in both 2-pair and 4-pair modes.

Detection is always performed on a per-channel basis.

Figure 14.

FIRST

DETECTION

POINT

SECOND

DETECTION

POINT

VALID PD

25k SLOPE

240

160

0V–2V

OFFSET

VOLTAGE

9101123 F14

PD Detection

Table 8. Port Detection Status

MEASURED PD SIGNATURE

(TYPICAL)

PORT DETECTION RESULT

Incomplete or Not Yet Tested

Detect Status Unknown

VPD < 1V

Short Circuit

RPD < 17k

RSIG Too Low

17k < RPD < 29k

Detect Good, Single-Signature PD

RPD > 29k

RSIG Too High

RPD > 50k

Open Circuit

VPD > 10V

Port Voltage Outside Detect Range

Connection Check = INVALID

Connection Check Invalid

Connection Check = DUAL or

Channel Detection Results Differ

Refer to Channel Detect Results

Table 9. Channel Detection Status

MEASURED PD SIGNATURE

(TYPICAL)

CHANNEL DETECTION RESULT

Incomplete or Not Yet Tested

Detect Status Unknown

VPD < 1V

Short Circuit

CPD > 2.7μF

CPD Too High

RPD < 17k

RSIG Too Low

17k < RPD < 29k

Detect Good, Dual-Signature PD

RPD > 29k

RSIG Too High

RPD > 50k

Open Circuit

VPD > 10V

Channel Voltage Outside Detect Range

Connection Check = INVALID

Connection Check Invalid

Connection Check = SINGLE or

Channel Detection Results Match

Refer to Port Detect Result

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