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参数资料
| 型号： | DC859A |
| 厂商： | Linear Technology |
| 文件页数： | 32/32页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR LTC4267 |
| 设计资源： | DC859A Design File DC859A Schematic |
| 标准包装： | 1 |
| 主要目的： | 电源管理，以太网供电（POE） |
| 嵌入式： | 否 |
| 已用 IC / 零件： | LTC4267 |
| 已供物品： | 板 |
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LTC4267
9
4267fc
BLOCK DIAGRAM
4267 BD
VPORTN
BOLD LINE INDICATES HIGH CURRENT PATH
POUT
–
+
PGND
RCLASS
PWRGD
CONTROL
CIRCUITS
INPUT
CURRENT
LIMIT
POWER GOOD
CLASSIFICATION
CURRENT LOAD
1.237V
EN
375mA
140mA
9k
16k
–
+
EN
25k
SIGNATURE
RESISTOR
VPORTP
SIGDISA
–
+
–
+
SLOPE
COMP
CURRENT
RAMP
PVCC
GATE
DRIVER
NGATE
SENSE
200kHz
OSCILLATOR
UNDERVOLTAGE
LOCKOUT
Q
R
CURRENT
COMPARATOR
SHUTDOWN
COMPARATOR
SHUTDOWN
S
20mV
ITH/RUN
ERROR
AMPLIFIER
VFB
SOFT-
START
CLAMP
VCC
SHUNT
REGULATOR
SWITCHING
LOGIC AND
BLANKING
CIRCUIT
0.28V
PVCC <
VTURNON
0.3A
PVCC
–
+
1.2V
800mV
REFERENCE
OVERVIEW
The LTC4267 is partitioned into two major blocks: a
Powered Device (PD) interface controller and a current
mode yback switching regulator. The Powered Device
(PD) interface is intended for use as the front end of a
PD adhering to the IEEE 802.3af standard, and includes
a trimmed 25kΩ signature resistor, classication current
source, and an input current limit circuit. With these
functions integrated into the LTC4267, the signature and
power interface for a PD can be built that meets all the
requirements of the IEEE 802.3af specication with a
minimum of external components.
The switching regulator portion of the LTC4267 is a con-
stant frequency current mode controller that is optimized
for Power over Ethernet applications. The regulator is
designed to drive a 6V N-channel MOSFET and features
soft-start and programmable slope compensation. The
integrated error amplier and precision reference give the
PD designer the option of using a nonisolated topology
without the need for an external amplier or reference. The
LTC4267 has been specically designed to interface with
both IEEE compliant Power Sourcing Equipment (PSE)
and legacy PSEs which do not meet the inrush current
requirement of the IEEE 802.3af specication. By setting
the initial inrush current limit to a low level, a PD using
the LTC4267 minimizes the current drawn from the PSE
during start-up. After powering up, the LTC4267 switches
to the high level current limit, thereby allowing the PD to
consume up to 12.95W if an IEEE 802.3af PSE is present.
This low level current limit also allows the LTC4267 to
charge arbitrarily large load capacitors without exceeding
the inrush limits of the IEEE 802.3af specication. This
dual level current limit provides the system designer with
exibility to design PDs which are compatible with legacy
PSEs while also being able to take advantage of the higher
power available in an IEEE 802.3af system.
Using an LTC4267 for the power and signature interface
functions of a PD provides several advantages. The
LTC4267 current limit circuit includes an onboard 100V,
400mA power MOSFET. This low leakage MOSFET is
APPLICATIO S I FOR ATIO
WU
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