參數(shù)資料
型號(hào)： LTC4257CS8#TRPBF
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: SO; No of Pins: 8; Temperature Range: 0°C to +70°C
中文描述： DATACOM, NETWORK INTERFACE SUPPORT CIRCUIT, PDSO8
封裝： 0.150 INCH, LEAD FREE, PLASTIC, SOP-8
文件頁(yè)數(shù)： 20/20頁(yè)
文件大?。?/td> 258K
代理商： LTC4257CS8#TRPBF
LTC4257
9
4257fb
probing exceeds 75ms, the LTC4257 may overheat. In this
situation, the thermal protection circuit will engage and
disable the classification current source in order to protect
the part. The LTC4257 stays in classification mode until
the input voltage rises above the UVLO turn-on voltage.
Undervoltage Lockout
IEEE 802.3af dictates a maximum turn-on voltage of 42V
and a minimum turn-off voltage of 30V for the PD. In
addition, the PD must maintain large on-off hysteresis to
prevent resistive losses in the wiring between the PSE and
the PD from causing start-up oscillation. The LTC4257
incorporates an undervoltage lockout (UVLO) circuit that
monitors line voltage to determine when to apply power
to the PD load (Figure 5). Before power is applied to the
load, the VOUT pin is high impedance and at ground
potential since there is no charge on capacitor C1. When
the input voltage rises above the UVLO turn-on threshold,
the LTC4257 removes the classification load current and
turns on the internal power MOSFET. C1 charges up under
LTC4257 current limit control and the VOUT pin transitions
from 0V to VIN. This sequence is shown in Figure 1. The
LTC4257 includes a hysteretic UVLO circuit that keeps
power applied to the load until the input voltage falls
below the UVLO turn-off threshold. Once the input voltage
drops below –30V, the internal power MOSFET is turned
off and the classification load current is re-enabled.
C1 will discharge through the PD circuitry and the VOUT
pin will go to a high impedance state.
Input Current Limit
IEEE 802.3af specifies a maximum inrush current and also
specifies a minimum load capacitor between the GND and
VOUT pins. To control turn-on surge current in the system,
the LTC4257 integrates a current limit circuit with the
onboard power MOSFET and sense resistor to provide a
complete inrush control circuit without additional external
components. The LTC4257 limits input current to less
than the 400mA maximum specified by 802.3af, allowing
the load capacitor to ramp up to the line voltage in a
controlled manner. During this ramp up, a large amount of
power is dissipated in the power MOSFET. The LTC4257
Figure 5. LTC4257 Undervoltage Lockout
APPLICATIO S I FOR ATIO
WU
UU
GND
C1
5
F
MIN
VIN
8
4
VOUT 5
LTC4257
4257 F05
TO
PSE
UNDERVOLTAGE
LOCKOUT
CIRCUIT
PD
LOAD
CURRENT-LIMITED
TURN ON
+
INPUT
LTC4257
VOLTAGE
POWER MOSFET
0V TO UVLO*
OFF
>UVLO*
ON
*UVLO INCLUDES HYSTERESIS
RISING INPUT THRESHOLD
–39.2V
FALLING INPUT THRESHOLD
–30.5V
相關(guān)PDF資料
PDF描述
LTC4257IDD#PBF IEEE 802.3af PD Power over Ethernet Interface Controller; Package: DFN; No of Pins: 8; Temperature Range: -40°C to +85°C
LTC4257IDD#TRPBF IEEE 802.3af PD Power over Ethernet Interface Controller; Package: DFN; No of Pins: 8; Temperature Range: -40°C to +85°C
LTC4257IS8#PBF IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: -40°C to +85°C
LTC4257IS8#TRPBF IEEE 802.3af PD Power over Ethernet Interface Controller; Package: SO; No of Pins: 8; Temperature Range: -40°C to +85°C
LTC4259ACGW-1#PBF Quad IEEE 802.3af Power over Ethernet Controller with AC Disconnect; Package: SSOP; No of Pins: 36; Temperature Range: 0°C to +70°C
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參數(shù)描述
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LTC4257IDD#PBF 功能描述:IC CONTROLLER POE INTERFACE 8DFN RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標(biāo)準(zhǔn)包裝:50 系列:- 類型:熱交換控制器 應(yīng)用:-48V 遠(yuǎn)程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開(kāi)關(guān):無(wú) 電流限制:可調(diào) 電源電壓:11.5 V ~ 14.5 V 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:10-TFSOP，10-MSOP（0.118"，3.00mm 寬） 供應(yīng)商設(shè)備封裝:10-MSOP 包裝:管件
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