IEEE 802.3af/at PD Front End IC

Microsemi Proprietary and Confidential. PD70100/PD70200 Datasheet Revision 3.0

5

3.1

Detail Description

PD70100/PD70200 IC provides IEEE 802.3af/at compliant PD Front-End functions including Detection,

Physical Layer Classification, Two-Events Classification (PD70200 only), Auxiliary Voltage Output, Power

Good, Soft Start Current Limiting, Over-Current Protection, and Bulk Capacitor Discharge.

3.1.1

Detection

IEEE 802.3af/at compliant detection is provided by a 24.9 KΩ resistor connected between V and R

PP

DET

pin. R

pin is connected to VPN via an open drain MOSFET with a maximum specified RDS

of 50 Ω.

DET

IN

ON

Internal logic monitors V to VPN and connects the R

pin to VPN when the rising V to VPN

PP

IN

DET

IN

PP

IN

voltage is between 2.5 V and 10.1 V. When rising V to VPN voltage exceeds 10.1 V, the MOSFET is

PP

IN

switched off. Once above 10.1 V, falling V to VPN voltage between 2.45 V and 4.85 V will reconnect

PP

IN

R

pin to VPN .

DET

IN

3.1.2

Physical Layer Classification

Physical Layer (hardware) Classification per IEEE 802.3af/at is generated via a regulated reference

voltage of 1.2 V, switched onto the R

pin. Internal logic monitors the V to VPN voltage and

CLASS

PP

IN

connects the 1.2 V reference to R

pin at a rising V to VPN voltage threshold between 11.1 V and

CLASS

PP

IN

13.5 V. Once V to VPN has exceeded the rising threshold, there is a 1 V minimum hysteresis between

PP

IN

the V rising (turn-on) threshold and the V falling (turn-off) threshold.

PP

PP

The 1.2 V reference stays connected to the R

pin until the V to VPN rising voltage exceeds the

CLASS

PP

IN

upper turn-off threshold of 20.9 V to 23.9 V. The 1.2 V reference voltage is disconnected from the RCLASS

pin at V to VPN voltages above the upper threshold.

PP

IN

Classification current signature is provided via a resistor connected between R

pin and VPN . The

CLASS

IN

classification current is therefore the current drawn by the PD70100/PD70200 IC during the

classification phase, and is simply the 1.2 V reference voltage divided by the R

resistor value. The

CLASS

maximum current available at the R

pin is current limited to 55 mA (typical).

CLASS

3.1.3

Two-Events Detection and AT Flag

The PD70200 IC provides IEEE 802.3at Type 2 compliant detection of the “Two Events Classification

Signature”, and generation of the AT flag. This feature is available on the PD70200 IC only.

Simply put, the “Two Events Classification Signature” is a means by which an IEEE 802.3at Type 2 Power

Source can inform a compliant Power Device (PD) that it is AT Type 2 compliant, and as such is capable

of providing AT Type 2 power levels.

The Power Source communicates with a Type 2 compliant signature by toggling the V to VPN voltage

PP

IN

twice (2 “events”) during the Physical Layer Classification phase. The V to VPN voltage is toggled from

PP

IN

the Physical Layer Classification’s voltage level (13.5 V to 20.9 V) down to a voltage “Mark” level. Voltage

“Mark” level is specified as a V to VPN voltage of 4.9 V to 10.1 V.

PP

IN

PD70200 IC recognizes a V to VPN falling edge from Classification level to Mark level as being one

PP

IN

event of the Two-Events Signature. If two such falling edges are detected, PD70200 will assert AT flag by

means of an open drain MOSFET connected between AT_FLAG pin and VPN

.

OUT

AT_FLAG pin is active low; a low impedance state between AT_FLAG and VPN

indicates a valid Two-

OUT

Events Classification Signature was received, and the Power Source is AT Type 2 compliant.

AT_FLAG MOSFET is capable of 5 mA of current and can be pulled up to V .

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3.1.4

Soft Start and Inrush Current Protection

PD70100/PD70200 IC contains an internal isolation switch, that provides ground isolation between

Power Source and PD application during Detection and Classification phases. The isolation switch is a N-

channel MOSFET, wired in a common source configuration where the MOSFET’s Source is connected to

Power Source ground at VPN , and the MOSFET’s Drain is connected to application’s primary ground at

IN

VPN

.

OUT

Internal logic monitors V to VPN voltage and keeps the MOSFET in a high impedance state until V to

PP

IN

PP