IEEE 802.3af/at PD Front End IC

Microsemi Proprietary and Confidential. PD70100/PD70200 Datasheet Revision 3.0

7

3.1.6

Power Good

During Soft Start mode, the PD70100/PD70200 IC monitors VPN

to VPN differential voltage. When

OUT

IN

this voltage is less than 0.7 V (max.), the IC enters normal operation mode and the isolation switch

current limit is increased to 1.8 A (typical). At this same 0.7 V (max.) threshold the Power Good signal is

asserted by means of an open drain MOSFET between PGOOD and VPN

.

OUT

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

indicates the Soft Start

OUT

mode has finished and the isolation switch has transitioned into normal operating mode.

PGOOD MOSFET can handle current of 5 mA and can be pulled up to V .

PP

3.1.7

Auxiliary Voltage Output

PD70100/PD70200 IC provides a 10.5 V (typical) regulated output to be used as a start-up supply for DC

/DC controllers whose V is provided via a bootstrap winding. This regulated supply is available at V

CC

AUX

pin, and is referenced to VPN

pin. V

supply is designed for low-duty operation, and should not be

OUT

AUX

designed as a primary housekeeping supply. The current capability is continuous 2 mA, with 10 mA peak

(≤ 10 ms). V

output is current-limited at 10 mA (min.).

AUX

For stability, the V

regulator requires a minimum of 4.7 µF ceramic capacitor connected directly

AUX

between V

and VPN

pins.

AUX

OUT

3.1.8

Thermal Protection

Both PD70100 and PD70200 IC include temperature sensors which individually monitor both the

isolation MOSFET and the Classification Current Source for over temperature conditions. In case of an

over temperature condition, the sensor will activate protection circuitry which will disconnect its

respective monitored function.

3.1.9

Bulk Capacitor Discharge

The bulk capacitor discharge circuitry eliminates the need to place a diode in series with the V line to

PP

prevent an application’s bulk capacitance from discharging through the detection resistor and the

isolation switch MOSFET’s body diode. Discharge current through the detection resistor can cause

failure of the detection signature in cases where a PD is connected and the bulk capacitance is not fully

discharged.

During normal operation, PD70100/PD70200 IC continuously monitors voltage at V to VPN . Should V

PP

IN

PP

to VPN voltage fall below isolation switch turn-off threshold (31 V to 34 V), isolation switch MOSFET is

IN

immediately placed in a high-impedance state. At this point the internal logic monitors the voltage at VPP

to VPN

. If V to VPN

voltage is between 1.5 V to 32 V, a 23 mA (min.) constant current source is

OUT

PP

OUT

connected across the V and VPN

pins. This constant current source provides bulk capacitor

PP

OUT

discharge.

A 220 µF bulk capacitance can be discharged from 32 V to 1.5 V in a maximal period of 292 ms.