MAX5945 datasheet(13/44 Pages) MAXIM

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agement where it detects a PD that draws more current

than the allowable amount for its class. The MAX5945’s

extensive programmability enhances system flexibility

and allows for uses in other applications.

The MAX5945 has four different operating modes: auto

mode, semi-auto mode, manual mode, and shutdown

mode (see the Operation Modes section). A special

watchdog feature allows the hardware to gracefully

take over control if the software/firmware crashes. A

cadence timing feature allows the MAX5945 to be used

in midspan systems.

The MAX5945 provides input undervoltage lockout,

input undervoltage detection, input overvoltage lockout,

overtemperature protection, output-voltage slew-rate

limit during startup, power-good status, and fault

status. The MAX5945’s programmability includes

gate-charging current, current-limit threshold, startup

timeout, overcurrent timeout, autorestart duty cycle, PD

disconnect AC detection threshold and PD disconnect

detection timeout.

The MAX5945 communicates with the system

microcontroller through an I2C-compatible interface.

The MAX5945 features separate input and output data

lines (SDAIN and SDAOUT) for use with optocoupler

isolation. The MAX5945 is a slave device. Its four

address inputs allow 16 unique MAX5945 addresses. A

separate INT output and four independent shutdown

inputs (SHD_) allow fast interrupt signals between the

MAX5945 and the microcontroller. A RESET input

allows hardware reset of the device.

Reset

Reset is a condition the MAX5945 enters after any of

the following conditions:

•

After power-up (VEE and VDD rise above their UVLO

thresholds).

•

Hardware reset. The RESET input is driven low and

up high again any time after power-up.

•

Software reset. Writing a 1 into R1Ah[4] any time

after power-up.

•

Thermal shutdown.

During a reset, the MAX5945 resets its register map to

the reset state as shown in Table 30 and latches in the

state of AUTO (pin 35) and MIDSPAN (pin 2). During

normal operation, changes at the AUTO and MIDSPAN

inputs are ignored. While the condition that caused the

reset persists (i.e., high temperature, RESET input low,

or UVLO conditions) the MAX5945 will not acknowl-

edge any addressing from the serial interface.

Port Reset (R1Ah[3:0])

Set high anytime during normal operation to turn off

power and clear the events and status registers of the

corresponding port. Port reset only resets the events

and status registers.

Operation Modes

The MAX5945 contains four independent but identical

state machines to provide reliable and real-time control

of the four network ports. Each state machine has four

different operating modes: auto, semi-auto, manual,

and shutdown. Auto mode allows the device to operate

automatically without any software supervision. Semi-

auto mode, upon request, continuously detects and

classifies a device connected to a port but does not

power up that port until instructed by software. Manual

mode allows total software control of the device and is

useful in system diagnostic. Shutdown mode terminates

all activities and securely turns off power to the ports.

Switching between AUTO, SEMI, or MANUAL mode

does not take effect until the part finishes its current

task. When the port is set into SHUTDOWN mode, all

the port operations are immediately stopped and the

port remains idle until SHUTDOWN is exited.

Automatic (AUTO) Mode

Enter automatic (AUTO) mode by forcing the

AUTO input high prior to a reset, or by setting

R12h[P_ M1,P_M0] to [1,1] during normal operation

(see Tables 15 and 15a). In AUTO mode, the MAX5945

performs detection, classification, and powers up the

port automatically once a valid PD is detected at the

port. If a valid PD is not detected at the port, the

MAX5945 repeats the detection routine continuously

until a valid PD is detected.

Going into AUTO mode, the DET_EN and CLASS_EN

bits are set to high and stay high unless changed by

software. Using software to set DET_EN and/or

CLASS_EN low causes the MAX5945 to skip detection

and/or classification. As a protection, disabling the

detection routine in AUTO mode will not allow the corre-

sponding port to power up, unless the DET_BYP

(R23H[4]) is set to 1.

The AUTO status is latched into the register only during

a reset. Any changes to the AUTO input after reset is

ignored.

Semi-Automatic (SEMI) Mode

Enter semi-automatic (SEMI) mode by setting

R12h[P_M1,P_M0] to [1,0] during normal operation

(see Tables 15 and 15a). In SEMI mode, the MAX5945,

upon request, performs detection and/or classification

repeatedly but does not power up the port(s), regard-

less of the status of the port connection.

Quad Network Power Controller

for Power-Over-LAN

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