+48V, Single-Port Network Power Switch

For Power-Over-LAN

18

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This overcurrent timeout enables the MAX5922 to operate

in a periodic overcurrent condition without causing a fault

(see Figure 9).

Power-OK (POK)

Zero-Current Detection

Zero-current detection is enabled if ZC_EN is high and

only after the startup period has finished (indicated by

350ms, a zero-current fault is generated. The MOSFET

is turned off and

ZC is latched low. The MAX5922A and

the MAX5922B/MAX5922C (with DET_DIS = low) imme-

diately begin a PD detection sequence, regardless of

the status of the LATCH input.

ZC is unlatched and

goes high impedance after a PD is detected.

ZC is also

high impedance during initial power-up. When

DET_DIS is high (MAX5922B/MAX5922C), a zero-cur-

rent fault shuts down the MOSFET and the EN pin

needs to be toggled to unlatch the fault.

zero and a zero-current fault is not generated. Bring

ZC_EN low to disable the zero-current detection func-

tion.

ZC stays high impedance in this mode.

Thermal Shutdown

If the MAX5922 die temperature reaches +150

°C, an

overtemperature fault is generated. The MOSFET turns

off and

FAULT goes low. The MAX5922 die tempera-

ture must cool down below 120

°C before the overtem-

perature fault condition is removed (see Fault

Management section).

Fault Report (

FAULT)

FAULT goes low when there is an overcurrent fault and/or

an overtemperature fault.

FAULT is open-drain otherwise.

After a fault, the

FAULT signal is latched low. FAULT is

unlatched at the beginning of the next power mode.

Fault Management

The MAX5922 offers either latched-off or auto-retry fault

management configurable by the LATCH input.

Bringing LATCH high puts the device into latch mode

while pulling LATCH low selects the autoretry option.

In latch mode, the MAX5922 turns the MOSFET off and

keeps it off after an overcurrent fault or an over-temper-

ature fault. After the fault condition goes away, recycle

the power supplies or toggle the EN pin low and high

again to unlatch the part. However, the part waits a

condition and resuming normal operation.

In autoretry mode, the MAX5922 turns the MOSFET off

after an overcurrent or overtemperature fault. After the

period (1.92s) and then automatically restarts and

enters the PD detection mode (MAX5922A and

MAX5922B/MAX5922C with DET_DIS low). If DET_DIS

is high (MAX5922B/MAX5922C), the MAX5922B/

MAX5922C automatically restart into the power-up

overtemperature condition, the MAX5922 waits for its

die temperature to cool down below the hysteresis level

Detection Collision Avoidance

Detection collision avoidance is enabled by connecting

ing it to DGND. When DCA is high, the MAX5922A acti-

detection during PD detection mode. During this back-

off time, the MAX5922A turns off the MOSFET and dri-

ves the OUT pin to high impedance. This function is

required by the IEEE 802.3af standard if the PSE

MAX5922A starts a PD detection sequence. The

MAX5922B has this function internally disabled and the

MAX5922C has this function internally enabled.

t

0V

0V

Figure 9. Overcurrent Response