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LTC4267 Datasheet(PDF) 4 Page - Linear Technology

Part No. LTC4267
Description  Power over Ethernet IEEE 802.3af PD Interface with Integrated Switching Regulator
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LTC4267 Datasheet(HTML) 4 Page - Linear Technology

 
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LTC4267
4
4267f
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: PVCC internal clamp circuit self regulates to 9.4V with respect to
PGND.
Note 3: The LTC4267 operates with a negative supply voltage in the range
of – 1.5V to – 57V. To avoid confusion, voltages for the PD interface
are always referred to in terms of absolute magnitude. Terms such as
“maximum negative voltage” refer to the largest negative voltage and
a “rising negative voltage” refers to a voltage that is becoming more
negative.
Note 4: The LTC4267 is designed to work with two polarity protection
diode drops between the PSE and PD. Parameter ranges specified in the
Electrical Characteristics section are with respect to this product pins and
are designed to meet IEEE 802.3af specifications when these diode drops
are included. See the Application Information section.
Note 5: Signature resistance is measured via the two-point ΔV/ΔI method
as defined by IEEE 802.3af. The PD signature resistance is offset from the
25kΩ to account for diode resistance. With two series diodes, the total PD
resistance will be between 23.75kΩ and 26.25kΩ and meet IEEE 802.3af
specifications. The minimum probe voltages measured at the LTC4267
pins are – 1.5V and – 2.5V. The maximum probe voltages are – 8.5V and
– 9.5V.
Note 6: The PD interface includes hysteresis in the UVLO voltages to
preclude any start-up oscillation. Per IEEE 802.3af requirements, the PD
will power up from a voltage source with 20Ω series resistance on the first
trial.
Note 7: Dynamic Supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 8: IVPORTN_CLASS does not include classification current
programmed at the RCLASS pin. Total current in classification mode will be
IVPORTN_CLASS + ICLASS (See note 9).
Note 9: ICLASS is the measured current flowing through RCLASS. ΔICLASS
accuracy is with respect to the ideal current defined as ICLASS = 1.237/
RCLASS. The current accuracy does not include variations in RCLASS
resistance. The total classification current for a PD also includes the IC
quiescent current (IVPORTN_CLASS). See Applications Information.
Note 10: For the DHC package, this parameter is assured by design and
wafer level testing.
Note 11: To disable the 25kΩ signature, tie SIGDISA to VPORTP or hold
SIGDISA high with respect to VPORTN. See Applications Information.
Note 12: The switching regulator is tested in a feedback loop that servos
VFB to the output of the error amplifier while maintaining ITH/RUN at the
midpoint of the current limit range.
Note 13: IPOUT_LEAK includes current drawn through POUT by the power
good status circuit. This current is compensated for in the 25kΩ signature
resistance and does not affect PD operation.
Note 14: The LTC4267 PD Interface includes thermal protection. In the
event of an overtemperature condition, the PD interface will turn off
the switching regulator until the part cools below the overtemperature
limit. The LTC4267 is also protected against thermal damage from
incorrect classification probing by the PSE. If the LTC4267 exceeds the
overtemperature threshold, the classification load current is disabled.
Note 15: The PD interface includes dual level input current limit. At turn-
on, before the POUT load capacitor is charged, the PD current level is set
to a low level. After the load capacitor is charged and the POUT – VPORTN
voltage difference is below the power good threshold, the PD switches to
high level current limit. The PD stays in high level current limit until the
input voltage drops below the UVLO turn-off threshold.
Note 16: Peak current sense voltage is reduced dependent on duty cycle
and an optional external resistor in series with the SENSE pin (RSL). For
details, refer to the programmable slope compensation feature in the
Applications Information section.
Note 17: Guaranteed by design.
Note 18: The PD interface includes overtemperature protection that is
intended to protect the device from momentary overload conditions.
Junction temperature will exceed 125°C when overtemperature protection
is active. Continuous operation above the specified maximum operating
junction temperature may impair device reliability.
ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
tRISE
NGATE Drive Rise Time
CLOAD = 3000pF, PVCC – PGND = 8V
40
ns
tFALL
NGATE Drive Fall Time
CLOAD = 3000pF, PVCC – PGND = 8V
40
ns
VIMAX
Peak Current Sense Voltage
RSL = 0, PVCC – PGND = 8V (Note 16)
90
100
115
mV
ISLMAX
Peak Slope Compensation Output Current
PVCC – PGND = 8V (Note 17)
5
µA
tSFST
Soft-Start Time
PVCC – PGND = 8V
1.4
ms
TSHUTDOWN
Thermal Shutdown Trip Temperature
(Notes 14, 18)
140
°C


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