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參數(shù)資料
| 型號： | LTC4257IDD#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 網(wǎng)絡(luò)接口 |
| 英文描述： | IEEE 802.3af PD Power over Ethernet Interface Controller; Package: DFN; No of Pins: 8; Temperature Range: -40°C to +85°C |
| 中文描述： | DATACOM, NETWORK INTERFACE SUPPORT CIRCUIT, PDSO8 |
| 封裝： | 3 X 3 MM, LEAD FREE, PLASTIC, MO-229WEED-1, DFN-8 |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 258K |
| 代理商： | LTC4257IDD#PBF |
LTC4257
3
4257fb
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.
Note 3: The LTC4257 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 is designed to work with two polarity protection
diodes between the PSE and PD. Parameter ranges specified in the
Electrical Characteristics are with respect to LTC4257 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 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
pins are –1.5V and –2.5V. The maximum probe voltages are –8.5V and
–9.5V.
Note 6: The LTC4257 includes hysteresis in the UVLO voltages to preclude
any start-up oscillation. Per IEEE 802.3af requirements, the LTC4257 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: 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 11: The LTC4257 includes smart thermal protection. In the event of
an overtemperature condition, the LTC4257 will reduce the input current
limit by 50% to reduce the power dissipation in the package. If the part
continues heating and reaches the shutdown temperature, the current is
reduced to zero until the part cools below the overtemperature limit. The
LTC4257 is also protected against thermal damage from incorrect
classification probing by the PSE. If the LTC4257 exceeds the
overtemperature trip point, the classification load current is disabled.
ELECTRICAL CHARACTERISTICS
RSIGNATURE
Signature Resistance
–1.5V
≤ VIN ≤ –9.5V, VOUT Tied to GND,
●
23.25
26.00
k
IEEE 802.3af 2-Point Measurement (Notes 4, 5)
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 = 300mA, 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 10)
●
150
A
ILIMIT
Input Current Limit
VIN = – 48V, VOUT = –43V (Note 11)
●
300
350
400
mA
ILIMIT_WARM
Overtemperature Input Current Limit
(Note 11)
188
mA
TOVERTEMP
Overtemperature Trip Temperature
(Note 11)
120
°C
TSHUTDOWN
Thermal Shutdown Trip Temperature
(Note 11)
140
°C
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