STE12PS datasheet(9/44 Pages) STMICROELECTRONICS

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STE12PS

Functional description

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Functional description

The STE12PS architecture provides a complete PSE interface and smart digital controller to

efficiently manage the functions in a PoE system. All operations can be controlled through

R/W registers via a standard I2C bus interface.

The STE12PS is designed to control power delivery of up to 12 separate lines. This is

performed by controlling 12 integrated, power MOS transistors connected to the low side of

the line - monitoring the line voltage and sensing line current by means of external, series

sensing resistors (one per port). Turning on a port means to switch the relative MOS

transistor thus controlling the inrush current in order to rise the port voltage up to 48V

(typical battery voltage) after a valid PD signature has been detected. The flexibility of the

STE12PS allows the user to select a suitable system configuration: 12 "standard", 4 or 6

"boosted" 30W channels, by means of pins CH_NUMn. Also, one can select the type of

architecture (Endpoint PSE/ Alternative A or Midspan PSE/Alternative B) for all channels via

pin A_BN_SEL.

Some typical applications for the STE12PS include:

●

Ethernet switches/routers

●

Midspan power supplies

●

IP-PBX

●

WLAN access points

3.1

Operating modes

The digital controller can operate in one of five possible modes for all the channels,

selectable through the Global Configuration registers: Stand-by, Auto, Semi Auto, Manual or

Power Down.

When the reset condition is removed, the controller defaults to Power Down mode if the

AUTO_START pin is tied low; if AUTO_START is tied HIGH the mode is configured in AUTO.

The mode can be changed only during a limited amount of time (100ms), after the reset is

released, accessing the Global Configuration registers before the detection procedure is

started, or placing the device in STAND-BY mode via the I2C interface.

The characteristics of the Five possible operating modes are described below:

●

STAND-BY: the controller allows only the read write operations suitable for changing

programmability. To enable this mode set the reset bit 1 of the REG0x05.

●

AUTO: the controller autonomously performs detection, classification and Power ON

command without the need of host commands. A subset of status flags stored in the

channels monitor registers is reported externally through the Status Flag Notifies pins

allowing operation without the presence of the host controller.

●

SEMIAUTO: after a triggering command the controller autonomously performs

detection and classification waiting a dedicated command from host processor for the

power on. Based on the detection and classification results reported in the Channels

Status registers, the host controller can decide to power on the selected channel. The

disconnection of a channel is automatic as in the AUTO mode, unless disabled.

●

MANUAL: any action is performed manually. The host controller has the responsibility

to force any state transition in the FSM. Then based on the measures performed

automatically by the ADC on several parameters, the host controller can decide to

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