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参数资料
| 型号： | LTC4257CS8-1#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: 0°C to +70°C |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SO-8 |
| 文件页数： | 14/20页 |
| 文件大小： | 265K |
| 代理商： | LTC4257CS8-1#PBF |
LTC4257-1
3
42571fb
VIH
Signature Disable
With Respect to VIN,
High Level Input Voltage
High Level Invalidates Signature (Note 10)
●
357
V
VIL
Signature Disable
With Respect to VIN,
Low Level Input Voltage
Low Level Enables Signature
●
0.45
V
RINPUT
Signature Disable
With Respect to VIN
Input Resistance
●
100
k
VPG_OUT
Power Good Output Low Voltage
I = 1mA, VIN = – 48V, PWRGD Referenced to VIN
●
0.5
V
Power Good Trip Point
VIN = –48V, Voltage Between VIN and VOUT (Note 9)
VPG_THRES_FALL
VOUT Falling
●
1.3
1.5
1.7
V
VPG_THRES_RISE
VOUT Rising
●
2.7
3.0
3.3
V
IPG_LEAK
Power Good Leakage
VIN = 0V, PWRGD FET Off, VPWRGD = 57V
●
1
A
RON
On-Resistance
I = 350mA, VIN = – 48V, Measured from VIN to VOUT
1.0
1.6
(Note 9)
●
2.0
IOUT_LEAK
VOUT Leakage
VIN = 0V, Power MOSFET Off, VOUT = 57V (Note 11)
●
150
A
ILIMIT_HIGH
Input Current Limit, High Level
VIN = – 48V, VOUT = –43V (Notes 12, 13)
0
°C ≤ TA ≤ 70°C
●
350
375
400
mA
–40
°C ≤ TA ≤ 85°C
●
340
375
400
mA
ILIMIT_LOW
Input Current Limit, Low Level
VIN = – 48V, VOUT = –43V (Notes 12, 13)
●
100
140
180
mA
TSHUTDOWN
Thermal Shutdown Trip Temperature
(Notes 12, 14)
140
°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
The
● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 3)
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: All voltages are with respect to GND pin unless otherwise noted.
Note 3: The LTC4257-1 operates with a negative supply voltage in the
range of –1.5V to –57V. To avoid confusion, voltages in this data sheet 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 LTC4257-1 is designed to work with two polarity protection
diode drops between the PSE and PD. Parameter ranges specified in the
Electrical Characteristics are with respect to LTC4257-1 pins and are
designed to meet IEEE 802.3af specifications when these diode drops are
included. See Applications Information.
Note 5: Signature resistance is measured via the 2-point
V/I method as
defined by IEEE 802.3af. The LTC4257-1 signature resistance is offset
from 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 specifications. The minimum probe voltages measured at the
LTC4257-1 pins are –1.5V and –2.5V. The maximum probe voltages are
–8.5V and –9.5V.
Note 6: The LTC4257-1 includes hysteresis in the UVLO voltages to
preclude any start-up oscillation. Per IEEE 802.3af requirements, the
LTC4257-1 will power up from a voltage source with 20
series
resistance on the first trial.
Note 7: IIN_CLASS does not include classification current programmed at
Pin 2. Total supply current in classification mode will be IIN_CLASS + ICLASS
(see Note 8).
Note 8: ICLASS is the measured current flowing through RCLASS.
ICLASS accuracy is with respect to the ideal current defined as
ICLASS = 1.237/RCLASS. The current accuracy specification does not
include variations in RCLASS resistance. The total classification current for
a PD also includes the IC quiescent current (IIN_CLASS). See Applications
Information.
Note 9: For the DD package, this parameter is assured by design and
wafer level testing.
Note 10: To disable the 25k signature, tie SIGDISA to GND (
±0.1V) or hold
SIGDISA high with respect to VIN. See Applications Information.
Note 11: IOUT_LEAK includes current drawn at the VOUT pin by the power
good status circuit. This current is compensated for in the 25k
signature
resistance and does not affect PD operation.
Note 12: The LTC4257-1 includes thermal protection. In the event of an
overtemperature condition, the LTC4257-1 will turn off the power MOSFET
until the part cools below the overtemperature limit. The LTC4257-1 is
also protected against thermal damage from incorrect classification
probing by the PSE. If the LTC4257-1 exceeds the overtemperature trip
point, the classification load current is disabled.
Note 13: The LTC4257-1 includes dual level input current limit. At turn-on,
before C1 is charged, the LTC4257-1 current level is set to the low level.
After C1 is charged and the VOUT – VIN voltage difference is below the
power good threshold, the LTC4257-1 switches to high level current limit.
The LTC4257-1 stays in high level current limit until the input voltage
drops below the UVLO turn-off threshold.
Note 14: This IC includes overtemperature protection that is intended to
protect the device during 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
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