Datasheet

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1366A
IEEE802.3AF/AT POWER-OVER-ETHERNET POWER SOURCING EQUIPMENT CONTROLLER
LTC4266
4
OPERATION
Introduction
The DC1366A demonstrates the features and capa-
bilities of the LTC4266, a quad controller for
IEEE802.3at Power Sourcing Equipment (PSE). The
DC1366A provides a quick and simple, fully compli-
ant PSE solution requiring only a V
EE
supply when
used in conjunction with the DC590B USB-to-I
2
C
interface board.
Supply Voltages
The IEEE802.3at standard requires the output volt-
age of a Type 2 PSE to be in the range of 51V to
57V. (The positive side is GND and the negative
side is V
EE
.) Obviously the V
EE
supply voltage should
be in this range for the sake of compliance; how-
ever, the LTC4266 is capable of operating with V
EE
down to 30V, the max undervoltage lockout (UVLO)
threshold.
Make sure to choose a V
EE
supply with enough
power to sustain all four ports at maximum load; if
the total load is too great for the power supply its
voltage may drop below the UVLO threshold, reset-
ting the LTC4266 and shutting off all the ports. The
worst case is when all four PDs are class 4: each
class 4 PD may draw up to 600mA, totaling 2.4A.
Therefore a V
EE
supply rated for at least 2.6A is rec-
ommended.
The V
DD
supply should nominally be 3.3V but the
LTC4266 is capable of operating over the range of
3.0V to 4.3V. (The UVLO threshold for the V
DD
sup-
ply is typically 2.2V.) The LTC4266 chip typically
draws only 1.1mA from the V
DD
supply; however,
LEDs and other components on the DC1366A board
also draw current from V
DD
, so the total load is typi-
cally 9mA to 26mA @ 3.3V depending on which
LEDs are lit.
Modes of Operation
The LTC4266 has four modes of operation:
■ Shutdown: Power is off, detection and classifi-
cation cycles are suspended.
■ Manual
: The port does not advance automati-
cally from detection to classification, to power
on. It waits for instructions from a host control-
ler via the I
2
C interface.
■ Semiauto : The port automatically advances to
classification after detecting a PD, but does not
turn on power to the PD until told to do so by
from a host controller via the I
2
C interface.
■ Auto : The port does everything autonomously.
The mode of each port can be set independently of
the others after power up via I
2
C commands.
The AUTO Pin
The AUTO pin determines several aspects of the
LTC4266 initial behavior. AUTO is sensed by the
LTC4266 at power up and after a reset.
If the AUTO pin is high then:
■ All
ports come up in AUTO mode. Any valid
PD will be turned on without software inter-
vention.
■ The current-sense resistors are assumed to be
0.25Ω (which they are on the DC1366A).
■ High power is enabled. After the LTC4266
classifies a PD it applies power and automati-
cally sets I
CUT
and I
LIM
appropriately for the
class. With high-power enabled a class 4 PD
will be able to draw >600mA without being cut
off.