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Data Sheet

LTC9101-2B/LTC9102

APPLICATIONS INFORMATION

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OPERATING MODES

The LTC9101-2B/LTC9102 controls up to 48 independent channels,

each of which can operate in one of three modes: manual, semi-au-

to, or auto. A fourth mode, shutdown, disables the port (see Table

9).

Table 9. Operating Modes

MODE

AUTO

MODE

PORT

MODE

DETECT/

CLASS

POWER-UP

AUTOMATIC

THRESHOLD

ASSIGNMENT

Auto

11b

Enabled at

Reset

Automatically

Yes

11b

Host Enabled

Automatically

Yes

Semi-

Auto

10b

Host Enabled

Upon Request

Yes

Manual 0

01b

Once Upon

Request

Upon Request

Yes

Shutdo

00b

Disabled

In manual mode, the port waits for instructions from the host system

before taking any action. It runs a single detection or classification

cycle when commanded to by the host, and reports the result in

its Port Status register. The host system can command the port to

apply or remove power at any time.

In semi-auto mode, the port repeatedly attempts to detect and

classify any PD attached to it. It reports the status of these attempts

back to the host, and waits for a command from the host before

applying power to the port. The host must enable detection and

classification. The detection and classification results must be valid

for power to be applied.

Auto mode operates the same as semi-auto mode except it will au-

tomatically apply power to the port if detection and classification re-

sults are valid. Auto mode will autonomously set the 2P Police and

ILIM-2P values based on the PSE assigned Class. This operational

mode may be entered by tying the PWRMD0 pin to VEE through a

resistor as listed in Table 14, or by changing the operating mode

section.

In shutdown mode the port is disabled and will not detect, class, or

power a PD.

Regardless of which mode it is in, the LTC9101-2B/LTC9102 will

remove power automatically from any port that generates a fault.

If disconnect detection is enabled, power will automatically be

removed from any port that generates a disconnect event. The host

controller may also command the port to remove power at any time.

Reset and PWRMD

The initial LTC9101-2B/LTC9102 configuration depends on the

state of PWRMD0 during reset. Reset occurs at power-up, whenev-

er RESET is pulled low, or when the global Reset All bit is set.

Changing the state of PWRMD0 after power-up will not change the

port behavior of the LTC9101-2B/LTC9102 until a reset occurs. The

PWRMD1 pin is reserved for future use.

With auto mode enabled via RPWRMD, each port will detect and

classify repeatedly until a PD is discovered. When a PD is discov-

ered, the port sets 2P Police according to the PSE assigned Class,

applies power to valid PDs, and removes power when a fault is

detected.

Table 10 shows the 2P Police value that is automatically set in

auto mode, based on the PSE assigned Class. The DC Disconnect

threshold is 7.0mA (typ) for all PSE assigned Classes and the 4P

Police value has no effect.

Table 10. Typical Auto Mode Power On Thresholds

PSE ASSIGNED CLASS

2P POLICE (W)

15.5

CLASS 4+, TYPE 1 LIMITED

15.5

CONNECTION CHECK

Connection Check Overview

IEEE 802.3bt introduces connection check, a mechanism for 4-pair

PSEs to discover a PD's signature configuration: single-signature,

dual-signature, or an invalid (non-PD) result. The connection check

result determines if and how a 4-pair capable PSE should provide

4-pair power.

In 802.3at, only one PD configuration was described; this is known

as a single-signature PD and is shown in Figure 36. A single-sig-

nature PD presents the same 25k detection resistor to both the

pairsets in parallel.

New in 802.3bt is the dual-signature PD. A dual-signature PD

presents two fully independent 25k detection signature resistors,

one to each pairset.

802.3bt 2-pair PSEs—including the LTC9101-2B/LTC9102—do not

perform connection check. Single- and dual-signature PDs are

treated the same: the PSE detects, classifies, and applies power

to a single pairset. High-power PDs are demoted by the PSE to a

lesser allocated Class. Dual-signature PDs are allocated power on

one pairset only.

DETECTION

Detection Overview

To avoid damaging network devices that were not designed to

tolerate DC voltage, a PSE must determine whether the connected

device is a valid PD before applying power. The IEEE 802.3 specifi-

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