LT4321

7

4321f

For more information www.linear.com/LT4321

applicaTions inForMaTion

Shutting down the LT4321 does not disconnect the load.

The external MOSFETs are shorted gate to source and

bridge current is carried by the MOSFETs’ body diodes.

The eight body diodes will act like two traditional diode

bridges.

At light load, the power dissipated in the forward drop of

the body diodes will be less than the power dissipated by

the LT4321 quiescent current. In applications with a low

power sleep mode, the LT4321 can optionally be shut

down to save power if the load current is less than 20mA.

EXTERNAL INTERFACE AND COMPONENT SELECTION

Bypass Capacitance

A 0.1μF ceramic capacitor must be placed across the

OUTP and OUTN pins.

In PD applications, the IEEE 802.3 standard limits the

LT4321 and the PD interface controller both need local

bypass capacitance, but they can share the same 0.1μF

capacitor. If the LT4321 and the PD interface controller

cannot both be positioned next to a shared bypass capaci-

placinga0.047μFceramicclosetotheLT4321andanother

0.047μF ceramic close to the PD interface controller.

A 10μF or greater capacitance must be connected across

OUTP and OUTN pins when the LT4321 is enabled. In

be connected by the PD interface controller’s hot swap

permanently connected between OUTP and OUTN.

Figure 2. Leakage Current at 125°C

Table 1. Conditions for Ideal Bridge Mode on IN12/IN36

PoE MODE

OUTP

EN | EN

IN12

IN36

IN45

IN78

TG12

TG36

BG12

BG36

Detect/Class

X

X

X

X

X

OFF

Class/Inrush

O

Power ON

1

> OUTP

< OUTN

X

X

ON

OFF

OFF

ON

< OUTN

> OUTP

OFF

ON

ON

OFF

|IN12 – IN36| <

OUTP – OUTN

> OUTN

OFF

< OUTP

Table 2. Conditions for Ideal Bridge Mode on IN45/IN78

PoE MODE

OUTP

EN | EN

IN12

IN36

IN45

IN78

TG45

TG78

BG45

BG78

Detect/Class

X

X

X

X

X

OFF

Class/Inrush

O

Power ON

1

X

X

> OUTP

< OUTN

ON

OFF

OFF

ON

< OUTN

> OUTP

OFF

ON

ON

OFF

|IN45 – IN78| <

OUTP – OUTN

> OUTN

OFF

< OUTP

0

0

150

200

300

15

4321 F02

100

50

250

5

10

20

25

LT4321 SHUTDOWN MODE

B2100 SCHOTTKY BRIDGE