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参数资料
| 型号： | LTC4259CGW#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 4-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO36 |
| 封装： | 0.300 INCH, PLASTIC, SSOP-36 |
| 文件页数： | 13/32页 |
| 文件大小： | 324K |
| 代理商： | LTC4259CGW#PBF |
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LTC4259
20
4259i
The DC disconnect feature can be disabled by clearing the
corresponding DC Discon Enable bits in the Disconnect
register (13h). The tDIS timer duration can be programmed
by bits 1 and 0 of register 16h.
The LTC4259 implements a variety of current sense and
limit thresholds to control current flowing through the
port. Figure 15 is a graphical representation of these
thresholds and the action the LTC4259 takes when
currrent crosses the thresholds.
AC DISCONNECT
AC disconnect is an alternate method of sensing the pres-
ence or absence of a PD by monitoring the port impedance.
The LTC4259 forces a signal, amplified from the OSCIN pin,
out of the DETECT pins and onto the Power over Ethernet
connection. It calculates the connection impedance from
ohm’s law, ZPORT=VAC/IAC.LikeDCdisconnect,theACdis-
connect sensing circuitry controls the disconnect timer.
When the connection impedance rises (AC current falls
below IACDMIN) due to the removal of the PD, the discon-
nect timer counts up. If the impedance remains high (AC
current remains below IACDMIN), the disconnect timer
counts to tDIS, the port is turned off and the port’s discon-
nect bit in the Fault Register is set. If connection imped-
ance falls (AC current rises above IACDMIN) before maximal
count of the disconnect timer, the timer resets and the port
remains powered.
Like DC disconnect, AC disconnect can also be disabled by
clearing the corresponding AC Discon Enable bits in the
Disconnect register (13h). AC disconnect is also affected
by the tDIS duration programmed in register 16h.
Unlike DC disconnect, AC disconnect has no continuous
time output to the timer. Rather, AC disconnect will reset
the timer once every cycle, 1/fOSCIN, of the OSCIN signal if
the port draws more than IACDMIN during that period.
Because of this behavior, the time to turn off the port after
PD removal, tDIS, may be up to one cycle of OSCIN
(1/fOSCIN) shorter than the delay programmed with the
tDIS1 and tDIS0 bits. Note that AC disconnect and DC
disconnect signals that reset the tDIS timer are ORed
together. Thus on a channel where both disconnect modes
are enabled, either disconnect sensing method can keep
the port powered even if the other reports that there is no
PD connected.
The AC disconnect circuitry senses the port and Power
over Ethernet connection from the DETECT pins. Connect
a 0.22
F 100V X7R capacitor (CDET) and a 1k resistor
(RDET) from the port’s DETECT pin to the port’s output as
shown in Figure 16. This provides an AC path for sensing
the channel impedance. The 1k resistor, RDET, limits
current flowing through this path during port power on
and power off.
Sizing of capacitors is critical to ensure proper function of
AC disconnect. CPSE (Figure 16) controls the connection
impedance on the PSE side. Its capacitance must be kept
low enough for AC disconnect to be able to sense the PD.
For operation near 100Hz, use a CPSE of 0.1F or less. On
the other hand, CDET has to be large enough to pass the
signal at the frequency of OSCIN. For fOSCIN ≈ 100Hz, use
at least a 0.22
F 100V X7R capacitor. The sizes of CPSE,
CDET, RDET and the frequency, fOSCIN, are chosen to create
an economical, physically compact and functionally
robust system. Moreover, the complete Power over Ether-
net AC disconnect system (PSE, transformers, cabling,
PD, etc.) is complex; deviating from the recommended
values of CDET, RDET and CPSE is discouraged. Contact the
LTC Applications department for additional support.
APPLICATIO S I FOR ATIO
WU
UU
Figure 15. LTC4259 Current Sense and Limits
0mA
0mV
100mA
CURRENT
RS = 0.5
DC DIS-
CONNECT
CUT
(ICUT)
LIMIT
(ILIM)
SHORT
CIRCUIT
EFFECT
SENSE
n
VOLTAGE
50mV
200mA
100mV
300mA
150mV
400mA
200mV
500mA
250mV
600mA
300mV
CURRENT
LIMIT
PORT OFF IN tICUT
OR tSTART
PORT OFF IN 1
s
NORMAL
OPERATION
PORT OFF IN tDIS
4259 F15
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| LTC4260 | 制造商:LINER 制造商全称:Linear Technology 功能描述:UV, OV and Reverse Supply Protection Controller Low Operating Current: 125μA |
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| LTC4260CGN#PBF | 功能描述:IC CTLR HOT SWAP I2C 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:119 系列:- 类型:热交换控制器 应用:通用型，PCI Express? 内部开关:无 电流限制:- 电源电压:3.3V，12V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:80-TQFP 供应商设备封装:80-TQFP（12x12） 包装:托盘 产品目录页面:1423 (CN2011-ZH PDF) |
| LTC4260CGN#TR | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-CH 80V 24-Pin SSOP N T/R |
| LTC4260CGN#TRPBF | 功能描述:IC HOT SWAP CNTRL I2C 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:119 系列:- 类型:热交换控制器 应用:通用型，PCI Express? 内部开关:无 电流限制:- 电源电压:3.3V，12V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:80-TQFP 供应商设备封装:80-TQFP（12x12） 包装:托盘 产品目录页面:1423 (CN2011-ZH PDF) |
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