LT4295 datasheet(31/50 Pages) AD

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LTC9101-1/

LTC9102/LTC9103

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

below IINRUSH-2P, as appropriate per the PD configuration

and Class.

If inrush is not successful, power is removed and the

corresponding tSTART faults are set. Otherwise, the port

or channel, as appropriate, advances to power on and

the programmed current limiting thresholds are used as

described in the Current Cutoff and Limit section.

Port Power Policing

The power policing threshold (PCUT-4P) is monitored on a

per-port basis, up to 128W in 0.5W increments (typical).

When the total output power over a one second mov-

ing average exceeds the specified threshold, power is

removed from the port and the corresponding tCUT faults

are set.

In particular, the port policing feature may be used to

ensure delivery of PD Class power while staying below

100W Limited Power Source (LPS) requirements.

Current Cutoff and Limit

Each LTC9101-1/LTC9102/LTC9103 port includes two

current limiting thresholds (ICUT-2P and ILIM-2P), each with

a corresponding timer (tCUT and tLIM). Setting the ICUT-2P

and ILIM-2P thresholds depends on several factors: the PD

assigned Class, the main supply voltage (VEE), the PSE

Type (Type 3 or 4), and the MOSFET SOA.

A single set of programmable port ICUT-2P and ILIM-2P

thresholds is shared by both channels. The thresholds

should be set based on the classification result as shown

in Table 6 and Table 7. For a dual-signature PD assigned

unequal Classes, the highest Class is used to set the

thresholds. For example, a dual-signature PD assigned

Class 1 and Class 5 would enforce ICUT-2P and ILIM-2P

based on Class 5.

Per the IEEE specification, the LTC9101-1/LTC9102/

LTC9103 will allow the channel current to exceed ICUT-2P

for a limited period of time before removing power from

the port, or channel, as appropriate whereas it will actively

control the MOSFET gate drive to keep the channel cur-

rent below ILIM-2P. The channel does not take any action

to limit the current when only the ICUT-2P threshold is

exceeded, but does start the tCUT timer. If the current

POWER CONTROL

The primary function of the LTC9101-1/LTC9102/LTC9103

is to control power delivery to the PSE port. With the

LTC9101-1/LTC9102/LTC9103, a PSE port is composed

of either one or two power channels; each power channel

controls power delivery over a pairset. Within this section,

operation of 4-pair configured ports is defined per chan-

nel. When configured for 2-pair operation, only a single

power channel is present per port.

The LTC9101-1/LTC9102/LTC9103 delivers power by

controlling the gate drive voltage of an external power

MOSFET while monitoring the current (through an exter-

nal sense resistor) and the output voltage (across the

OUT pin).

The LTC9101-1/LTC9102/LTC9103 connects the VEE

power supply to the PSE port in a controlled manner,

meeting the power demands of the PD while minimizing

power dissipation in the external MOSFET and distur-

bances to the VEE backplane.

Inrush Control

When commanded to apply power to a port, the

LTC9101-1/LTC9102/LTC9103 ramps up the GATE pin

of one or both channels (as commanded), raising the

external MOSFET gate voltage in a controlled manner.

During a typical inrush, the MOSFET gate voltage will rise

until the external MOSFET is fully enhanced or the channel

reaches the inrush current limit (IINRUSH-2P). IINRUSH-2P is

set automatically by the PSE. When the PSE is applying

4-pair power to a single-signature PD assigned Class 0

to Class 4, IINRUSH-2P is 212.5mA (typical) per channel.

Otherwise, IINRUSH-2P is 425mA (typical) per channel.

The GATE pin will be servoed if channel current exceeds

IINRUSH-2P, actively limiting current to IINRUSH-2P. When

the GATE pin is not being servoed, the final VGS is 12V

(typical).

During inrush, each powered channel runs a timer (tSTART).

Each powered channel stays in inrush until tSTART expires.

When tSTART expires, the PSE inspects channel voltage

and current. When the PSE is applying power to a PD,

inrush is successful if the channel(s) are drawing current

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