ltc4267cgn-1 Linear Technology Corporation, ltc4267cgn-1 Datasheet - Page 4

• Manufacturer Part Number: ltc4267cgn-1
• Description: Power Over Ethernet Ieee 802.3af Pd Interface With Integrated Switching Regulator
• Manufacturer: Linear Technology Corporation

LTC4267-1
SYMBOL
t
t
V
I
t
T
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: P
PGND.
Note 3: The LTC4267-1 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 LTC4267-1 is designed to work with two polarity protection
diode drops between the PSE and PD. Parameter ranges specifi ed in the
Electrical Characteristics section are with respect to this product pins and
are designed to meet IEEE 802.3af specifi cations 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 defi ned by IEEE 802.3af. The PD signature resistance is offset from
the 25k to account for diode resistance. With two series diodes, the total
PD resistance will be between 23.75k and 26.25k and meet IEEE 802.3af
specifi cations. The minimum probe voltages measured at the LTC4267-1
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 fi rst
trial.
Note 7: Dynamic Supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 8: I
programmed at the R
I
Note 9: I
accuracy is with respect to the ideal current defi ned as I
4
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifi cations are at T
RISE
FALL
SLMAX
SFST
VPORTN_CLASS
SHUTDOWN
IMAX
VPORTN_CLASS
CLASS
VCC
internal clamp circuit self regulates to 9.4V with respect to
+ I
is the measured current fl owing through R
CLASS
PARAMETER
NGATE Drive Rise Time
NGATE Drive Fall Time
Peak Current Sense Voltage
Peak Slope Compensation Output Current
Soft-Start Time
Thermal Shutdown Trip Temperature
CLASS
does not include classifi cation current
(See note 9).
pin. Total current in classifi cation mode will be
CLASS
CLASS
A
= 1.237/
= 25°C. (Note 3)
. ΔI
CLASS
The
CONDITIONS
C
C
R
P
P
(Notes 13, 17)
LOAD
LOAD
SL
VCC
VCC
●
= 0, P
denotes the specifi cations which apply over the full operating
– P
– P
= 3000pF, P
= 3000pF, P
GND
GND
VCC
R
resistance. The total classifi cation current for a PD also includes the IC
quiescent current (I
Note 10: To disable the 25k signature, tie SIGDISA to V
SIGDISA high with respect to V
Note 11: The switching regulator is tested in a feedback loop that servos
V
midpoint of the current limit range.
Note 12: I
good status circuit. This current is compensated for in the 25k signature
resistance and does not affect PD operation.
Note 13: The LTC4267-1 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 LTC4267-1 is also protected against thermal damage from
incorrect classifi cation probing by the PSE. If the LTC4267-1 exceeds the
overtemperature threshold, the classifi cation load current is disabled.
Note 14: The PD interface includes dual level input current limit. At turn-
on, before the P
to a low level. After the load capacitor is charged and the P
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 15: Peak current sense voltage is reduced dependent on duty cycle
and an optional external resistor in series with the SENSE pin (R
details, refer to the programmable slope compensation feature in the
Applications Information section.
Note 16: Guaranteed by design.
Note 17: 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 specifi ed maximum operating
junction temperature may impair device reliability.
CLASS
FB
= 8V (Note 16)
= 8V
to the output of the error amplifi er while maintaining I
– P
. The current accuracy does not include variations in R
GND
VCC
VCC
POUT_LEAK
= 8V (Note 15)
– P
– P
GND
GND
OUT
VPORTN_CLASS
load capacitor is charged, the PD current level is set
includes current drawn through P
= 8V
= 8V
●
PORTN
). See Applications Information.
MIN
. See Applications Information.
90
TYP
100
140
1.4
40
40
5
OUT
PORTP
TH
by the power
MAX
115
OUT
/RUN at the
or hold
CLASS
– V
SL
PORTN
). For
UNITS
42671f
mV
ms
μA
ns
ns
°C