PD70210AL datasheet(6/24 Pages) MICROCHIP

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1.1

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.

1.1.1

Detection

IEEE 802.3af/at compliant detection is provided by a 24.9 KΩ resistor connected between VPP and RDET pin. RDET

pin is connected to VPNIN via an open drain MOSFET with a maximum specified RDSON of 50 Ω. Internal logic

monitors VPP to VPNIN and connects the RDET pin to VPNIN when the rising VPP to VPNIN voltage is between 2.5 V

and 10.1 V. When rising VPP to VPNIN voltage exceeds 10.1 V, the MOSFET is switched off. Once above 10.1 V,

falling VPP to VPNIN voltage between 2.45 V and 4.85 V will reconnect RDET pin to VPNIN.

1.1.2

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 RCLASS pin. Internal logic monitors the VPP to VPNIN voltage and connects the 1.2 V reference to

RCLASS pin at a rising VPP to VPNIN voltage threshold between 11.1 V and 13.5 V. Once VPP to VPNIN has exceeded

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

(turn-off) threshold.

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

voltages above the upper threshold.

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

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 RCLASS resistor value. The maximum current available at the

RCLASS pin is current limited to 55 mA (typical).

1.1.3

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 VPP to VPNIN voltage twice (2

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

VPP to VPNIN voltage of 4.9 V to 10.1 V.

PD70200 IC recognizes a VPP to VPNIN falling edge from Classification level to Mark level as being one 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 VPNOUT.

AT_FLAG pin is active low; a low impedance state between AT_FLAG and VPNOUT indicates a valid Two-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 VPP.

1.1.4

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 VPNIN, and

the MOSFET’s Drain is connected to application’s primary ground at VPNOUT.

Internal logic monitors VPP to VPNIN voltage and keeps the MOSFET in a high impedance state until VPP to VPNIN

voltage reaches turn-on threshold of 36 V to 42 V. Once VPP to VPNIN voltage exceeds this threshold, the MOSFET is

switched into one of two modes.

PD70100/PD70200

Functional Descriptions

Datasheet

DS00003639A-page 6

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