参数资料
型号: LTC4264IDE#PBF
厂商: Linear Technology
文件页数: 5/24页
文件大小: 0K
描述: IC CNTRLR PD INTERFACE 12-DFN
产品培训模块: Power over Ethernet
标准包装: 91
控制器类型: 以太网供电控制器(POE)
接口: IEEE 802.3af
电流 - 电源: 3mA
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 12-WFDFN 裸露焊盘
供应商设备封装: 12-DFN(4x3)
包装: 管件
LTC4264
13
4264f
During the inrush event as C1 is being charged, a large
amount of power is dissipated in the MOSFET. The LTC4264
is designed to accept this load and is thermally protected
to avoid damage to the onboard power MOSFET. If a
thermal overload does occur, the power MOSFET turns
off, allowing the die to cool. Once the die has returned to
a safe temperature, the LTC4264 automatically switches
to ILIMIT_LOW, and load capacitor C1 charging resumes.
The LTC4264 has the option of disabling the normal operat-
ing input current limit, ILIMIT_HIGH, for custom high power
PoE applications. To disable the current limit, connect
ILIM_EN to VIN. To protect the LTC4264 from damage when
the normal current limit is disabled, a safeguard current
limit, ILIMIT_DISA keeps the current below destructive
levels, typically 1.4A. Note that continuous operation at
or near the safeguard current limit will rapidly overheat
the LTC4264, engaging the thermal protection circuit. For
normal operations, oat the ILIM_EN pin. The LTC4264
maintains the ILIMIT_LOW inrush current limit for charging
the load capacitor regardless of the state of ILIM_EN. The
operation of the ILIM_EN pin is summarized in Table 3.
Table 3. Current Limit as a Function of ILIM_EN
STATE OF ILIM_EN
INRUSH CURRENT
LIMT
OPERATING INPUT
CURRENT LIMIT
Floating
ILIMIT_LOW
ILIMT_HIGH
Tied to VIN
ILIMIT_LOW
ILIMIT_DISA
POWER GOOD
The LTC4264 includes complementary power good outputs
(Figure 8) to simplify connection to any DC/DC converter.
Power Good is asserted at the end of the inrush event when
load capacitor C1 is fully charged and the DC/DC converter
can safely begin operation. The power good signal stays
active during normal operation and is de-asserted at power
off when the port drops below the UVLO threshold or in
the case of a thermal overload event.
For PD designs that use a large load capacitor and also
consume a lot of power, it is important to delay activa-
tion of the DC/DC converter with the power good signal.
If the converter is not disabled during the current-limited
turn-on sequence, the DC/DC converter will rob current
intended for charging up the load capacitor and create a
slow rising input, possibly causing the LTC4264 to go into
thermal shutdown.
APPLICATIONS INFORMATION
4264 BD
BOLD LINE INDICATES HIGH CURRENT PATH
PWRGD
POWER
NOT
GOOD
INRUSH COMPLETE
AND NOT IN THERMAL SHUTDOWN
VIN < UVLO OFF
OR THERMAL SHUTDOWN
POWER
GOOD
9
PWRGD
LTC4264
10
VOUT
8
VOUT
7
VIN 6
VIN
REF
UVLO
THERMAL SD
5
CONTROL
CIRCUIT
Figure 8. LTC4264 Power Good Functional and State Diagram
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