(

)

(

)

APD1

APD2

ADPTR_ON

APDEN

APDEN

APD1

APD2

ADPTR_OFF

APDEN

APDH

APD2

R

= R

V

V

V

R

+ R

V

=

V

V

R

´

-

´

-

( )

( )

BLNK

BLNK

R

k

= t

ns

W

TPS23754

TPS23754-1

TPS23756

SLVS885D – OCTOBER 2008 – REVISED DECEMBER 2009

www.ti.com

PIN DESCRIPTION

numerical values used in the following sections.

APD

switch, disabling the CLS output (see PPD pin description), and enabling the T2P output. A resistor divider is

recommended on APD when it is connected to an external adapter. The divider provides ESD protection,

leakage discharge for the adapter ORing diode, and input voltage qualification. Voltage qualification assures the

adapter output voltage is high enough that it can support the PD before the PoE current is cut off.

APD function as adapter voltage rises.

(1)

Place the APD pull-down resistor adjacent to the APD pin.

APD should be tied to ARTN when not used.

BLNK

Blanking provides an interval between GATE going high and the current-control comparators on CS actively

monitoring the input. This delay allows the normal turn-on current transient (spike) to subside before the

comparators are active, preventing undesired short duty cycles and premature current limiting.

Connect BLNK to ARTN to obtain the internally set blanking period. Connect a resistor from BLNK to ARTN for a

more accurate, programmable blanking period. The relationship between the desired blanking period and the

programming resistor is defined by Equation 2.

(2)

Place the resistor adjacent to the BLNK pin when it is used.

CLS

corresponding resistor values are listed in Table 1. The power assigned should correspond to the maximum

average power drawn by the PD during operation.

High-power PSEs may perform two classification cycles if Class 4 is presented on the first cycle. The TPS23754

presents the same (resistor programmed) class each cycle per the standard.

Table 1. Class Resistor Selection

POWER AT PD

RESISTOR

CLASS

NOTES

MINIMUM

MAXIMUM

(

Ω)

(W)

(W)

0

0.44

12.95

1270

Minimum may be reduced by pulsed loading. Serves as a catch-all default class.

1

0.44

3.84

243

2

3.84

6.49

137

3

6.49

12.95

90.9

4

12.95

25.5

63.4

Not allowed prior to IEEE 802.3at. Use to indicate a Type 2 PD (high power)

device per IEEE 802.3at.

8

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