Operation - Linear Technology DC1366B Manual

DEMO MANUAL DC1366B

operation

Introduction
The DC1366B demonstrates the features and capabilities
of the LTC4266, a quad controller for IEEE802.3at Power
Sourcing Equipment (PSE). The DC1366B provides a quick
and simple, fully compliant PSE solution requiring only
a V supply when used in conjunction with the DC590
EE
2
USB-to-I C interface board.
Supply Voltages
The IEEE802.3at standard requires the port output volt-
age of a type 2 PSE to be in the range of 50V to 57V. The
positive side is RTN and the negative side is V
supply voltage should be in this range for the sake of
compliance; however, the LTC4266 is capable of operat-
ing with V down to 30V, the max undervoltage lockout
EE
(UVLO) threshold.
Make sure to choose a V
EE
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, resetting 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 supply rated for at least 2.6A is
EE
recommended.
The V supply should nominally be 3.3V but the LTC4266
DD
is capable of operating over the range of 3.0V to 4.3V.
(The UVLO threshold for the V
The LTC4266 chip typically draws only 1.1mA from the
V supply; however, LEDs and other components on
DD
the DC1366B board also draw current from V
total load is typically 9mA to 26mA at 3.3V depending on
which LEDs are lit.
V to DGND Configurations
DD
The DC1366B, LTC4266 V
one of two ways. The default DC1366B configuration ties
the LTC4266 V pin to the AGND pin through a 0 Ohm
DD
resistor R10. The DGND pin is at –3.3V below the AGND
pin. The DC1366B can also be configured for a +3.3V at
V relative to AGND by removing R10 and installing a
DD
0Ω resistor at R9. This ties the LTC4266 DGND pin and
AGND pin.
4
. The V
EE
supply with enough power to
supply is typically 2.2V.)
DD
, so the
DD
supply can be configured in
DD
Modes of Operation
The LTC4266 has four modes of operation:
Shutdown: Ports are shutdown, detection and clas-
n
sification cycles are disabled.
Manual: The port does not advance automatically from
n
detection to classification, to power on. It waits for
instructions from a host controller via the I
Semiauto: The port automatically advances to clas-
n
sification 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
EE
AUTO Pin High: The LTC4266 operates autonomously.
n
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 pin high mode. Any valid
n
PD will be turned on without software intervention.
The current-sense resistors are assumed to be 0.25Ω
n
(which they are on the DC1366B).
High power is enabled. After the LTC4266 classifies a
n
PD it applies power and automatically sets I
appropriately for the class. With high-power enabled a
class 4 PD will be able to draw up to 600mA without
being cut off.
If the AUTO pin is low then:
All ports come up in shutdown mode. A host controller
n
must take action in order to power up any PDs.
The current-sense resistors are assumed to be 0.50Ω;
n
a host controller must change this to 0.25Ω for correct
operation of the DC1366B.
High power is disabled and is enabled by a host con-
n
troller.
2
C interface.
2
C interface.
CUT
and I
LIM
dc1366bf