Rainbow Electronics MAX5945 - Manual (Page 13)

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 I
2 C-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 (V EE and V DD 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.
MAX5945
Quad Network Power Controller
for Power-Over-LAN
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