LTC4267IGN-1-PBF datasheet(10/32 Pages) LINER

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LTC4267-1

42671f

avoid corrupting the 25k signature resistor while also sav-

ing board space and cost. In addition, the inrush current

limit requirement of the IEEE 802.3af standard can cause

large transient power dissipation in the PD. The LTC4267-1

is designed to allow multiple turn-on sequences without

overheating the miniature 16-lead package. In the event of

excessive power cycling, the LTC4267-1 provides thermal

overload protection to keep the onboard power MOSFET

within its safe operating area.

OPERATION

The LTC4267-1 PD interface has several modes of opera-

tion depending on the applied input voltage as shown in

Figure 1 and summarized in Table 1. These modes satisfy

the requirements deﬁned in the IEEE 802.3af speciﬁcation.

The input voltage is applied to the VPORTN pin and must

be negative relative to the VPORTP pin. Voltages in the data

sheet for the PD interface portion of the LTC4267-1 are

with respect to VPORTP while the voltages for the switch-

ing regulator are referenced to PGND. It is assumed that

PGND is tied to POUT. Note the use of different ground

symbols throughout the data sheet.

Table 1. LTC4267-1 Operational Mode

as a Function of Input Voltage

INPUT VOLTAGE

(VPORTN with RESPECT to VPORTP) LTC4267-1 MODE OF OPERATION

0V to – 1.4V

Inactive

–1.5V to –9.5V**

25k Signature Resistor Detection

–9.8V to –12.4V

Classiﬁcation Load Current Ramps up

from 0% to 100%

–12.5V to UVLO*

Classiﬁcation Load Current Active

UVLO* to –57V

Power Applied to Switching Regulator

*VPORTN UVLO includes hysteresis.

Rising input threshold

≅ –36.0V

Falling input threshold

≅ –30.5V

**Measured at LTC4267-1 pin. The LTC4267-1 meets the IEEE 802.3af 10V

minimum when operating with the required diode bridges.

APPLICATIO S I FOR ATIO

Figure 1. Output Voltage,

⎯P⎯W⎯R⎯G⎯D and PD

Current as a Function of Input Voltage

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