_________________________________________________________________________________________________________

Copyright © 2015

Microsemi

Page 14 of 20

Rev.2.0, 17-Jan-2017

CPG

– PoE BU

One Enterprise Aliso Viejo, CA 92656 USA

PD70101 / PD70201

Datasheet

Theory of Operation

General Description

PD70101/PD70201 IC integrates IEEE 802.3af/at compliant PD Front-End functions including Detection, Physical

Layer Classification, Two-Events Classification (PD70201 only), Power Good, Soft Start Current Limiting, Over-

Current Protection, and Bulk Capacitor Discharge with a PWM controller. The integrated PWM controller function

provides a PWM controller solution with a minimum requirement of external components.

Detection

IEEE 802.3af/at compliant detection is prov

ided by means of a 24.9KΩ resistor connected between VPP and RDET

pin. RDET pin is connected to VPN_IN via an open drain MOSFET with a maximum specified RDSON of 50Ω.

Internal logic monitors VPP to VPN_IN and connects the RDET pin to VPN_IN when the rising VPP to VPN_IN

voltage is between 1.1V and 10.1V. When rising VPP to VPN_IN voltages exceed 10.1V, the MOSFET is switched

off.

Once above 10.1V, falling VPP to VPN_IN voltage between 2.45V and 4.85V will reconnect RDET pin to

VPN_IN.

Physical Layer Classification

Physical Layer (hardware) Classification per IEEE 802.3af/at is generated via a regulated reference voltage of 1.2V,

switched onto the RCLASS pin. Internal logic monitors the VPP to VPN_IN voltage and connects the 1.2V reference

to RCLASS pin at a rising VPP to VPN_IN voltage threshold between 11.4V and 13.7V. Once VPP to VPN_IN has

exceeded the rising threshold, there is a 1V typical hysteresis between the VPP rising (turn-on) threshold and the

VPP falling (turn-off) threshold.

The 1.2V reference stays connected to the RCLASS pin until the VPP to VPN_IN rising voltage exceeds the upper

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

VPN_IN voltages above the upper threshold.

Classification current signature is provided via a resistor connected between RCLASS pin and VPN_IN.

The

classification current is therefore the current drawn by the PD70101/PD70201 IC during the classification phase, and

is simply the 1.2V reference voltage divided by the RCLASS resistor value. The maximum current available at the

RCLASS pin is current limited to 68mA (typical).

Two-Events Detection and AT Flag

The PD70201 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 PD70201 IC only.

Simply put, the “Two Events Classification Signature” is a mean 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 the Type 2 compliant signature by toggling the VPP to VPN_IN voltage twice (2

“events”) during the Physical Layer Classification phase. The VPP to VPN_IN voltage is toggled from the Physical

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

as a VPP to VPN_IN voltage of 4.9V to 10.1V.

PD70201 IC recognizes a VPP to VPN_IN falling edge from Classification level to Mark level as being one event of

the Two-Events Signature. If two such falling edges are detected, PD70201 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_OUT indicates a valid Two-Events

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

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

Soft Start and Inrush Current Protection

PD70101/PD70201 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