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The MAX5940B evaluation kit (EV kit) is a fully assembled
and tested surface-mount circuit board featuring
an Ethernet port, network powered device (PD) interface
controller circuit for -48V supply systems. The EV kit
uses the MAX5940B IEEE® 802.3af-compliant network PD
interface controller in an 8-pin SO package. The
MAX5940B EV kit can also evaluate the MAX5940D
rated for an absolute maximum input voltage of 90V.
The MAX5940B features an internal isolation switch that
limits inrush current. The MAX5940B is used in powerover-
LAN applications requiring DC power from an
Ethernet network port for PDs such as IP phones, wireless
access nodes, and security cameras.
The MAX5940B EV kit receives power from an IEEE
802.3af-compliant power sourcing equipment (PSE).
See the MAX5922 and MAX5935 data sheets for PSE
controllers. The PSE provides the required -44V to -57V
DC power over an unshielded twisted-pair Ethernet network
cable to the EV kit's RJ-45 jack. The EV kit features
a 10/100BASE-TX Voice-over-IP (VoIP) magnetic module
and two diode bridges for separating the DC power
provided by an endspan or midspan Ethernet system.
The EV kit demonstrates the full functionality of the
MAX5940B such as the PD detection signature, configurable
PD classification signature, programmable
inrush current, and undervoltage lockout (UVLO). All of
these features are configurable on the EV kit and additional
test points for voltage probing and interfacing
have been provided for the PD interface.
The MAX5940B EV kit also features a galvanically isolated
6W, 275kHz switching frequency flyback DC-DC converter,
which uses the MAX5014 current-mode PWM
controller. The MAX5940B's -48V output provides power
for the converter circuit. The DC-DC converter is configured
for an output voltage of 4.25V and provides up to
1.4A at the output. High efficiency up to 82.2% is
achieved using a single transistor flyback DC-DC converter
topology. The surface-mount transformer provides
1500V galvanic isolation for the output. UVLO, soft-start,
and thermal shutdown provide a robust 6W isolated
power supply.
The EV kit can be reconfigured for interfacing to an
external DC-DC converter for an additional 7W of output
power.
Warning: The MAX5940B EV kit operates with high voltages.
Dangerous voltages are present on this EV kit and
on equipment connected to it. Users who power up this
EV kit or power the sources connected to it must be careful
to follow safety procedures appropriate to working with
high-voltage electrical equipment.
Under severe fault or failure conditions, this EV kit may
dissipate large amounts of power, which could result in
the mechanical ejection of a component or of component
debris at high velocity. Operate this EV kit with
care to avoid possible personal injury.
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