STE12PS datasheet(10/44 Pages) STMICROELECTRONICS

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Functional description

STE12PS

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classify the channel and afterwards to issue the power on command. The STE12PS

controller can also automatically disconnect a channel in fault condition (if not enabled,

the STE12PS will notify automatically only a short circuit condition or an AC

disconnection event. Overload or DC disconnection is responsibility of the host

controller.) The host controller can also power on a channel skipping detection and/or

classification procedures.

●

POWER DOWN: the controller is put in power down state. No actions are performed

until the power down mode is removed.

For all operating modes, except power-down and stand-by, the power ON/OFF condition of

each channel can also be managed, directly, by the host processor or controller via a

dedicated command.

Moreover, the power removal procedure is performed automatically (also in MANUAL mode)

when a fault event has been detected (AC/DC disconnection, overload or overcurrent); this

behavior can be changed configuring appropriately some dedicated enable/disable bits of

channels event registers.

With Priority Management in AUTO mode and Smart-power management enabled, it is also

possible to set different priorities for different channels. The STE12PS will probe channels

starting from those with the highest priority

. In case of a shortage of available power, it is

also possible to disable powering of newly detected, lower priority ports until the highest

detected ones are served.

3.2

Detection and classification

3.2.1

Detection

The STE12PS looks for, in turn on the free available ports (according to the priority list if

enabled

), for a valid PD signature (25k

Ω slope characteristic) by driving two different voltage

levels at the port

(4V and 8V), and calculating the slope resistance/ conductance by

monitoring the current difference

. The equivalent circuit for the IEEE802.3af detection phase

is shown in

Figure 3 below.

Figure 3.

IEEE802.3af detection circuit

As detection is performed by multiplexing a common voltage generator. If more than one

port is connected to several PDs, an extra delay in the detection start will be introduced. See

Table 12: Electrical characteristics, parameter Tdetd.

P+

P-

Zsource

P+

P-

Zsource

P+

P-

Zsource

PC00103

D1(one per port) is external.

D2 (one per port) external is required only if

the AC_Disconnection function is used,

otherwise it is internally emulated.

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