參數(shù)資料
型號(hào)： LTC4252-1
廠商： Linear Technology Corporation
英文描述： TRANS ARRAY NPN/PNP SS MINI-6P
中文描述： 負(fù)電壓熱插拔控制器
文件頁(yè)數(shù)： 12/32頁(yè)
文件大?。?/td> 327K
代理商： LTC4252-1
LTC4252-1/LTC4252-2
12
425212f
OPERATIOU
Two modes of operation are possible during the time the
MOSFET is first turning on, depending on the values of
external components, MOSFET characteristics and nomi-
nal design current. One possibility is that the MOSFET will
turn on gradually so that the inrush into the load capaci-
tance remains a low value. The output will simply ramp to
–48V and the LTC4252 will fully enhance the MOSFET. A
second possibility is that the load current exceeds the soft-
start current limit threshold of [V
SS
(t)/20 – V
OS
]/R
S
. In this
case the LTC4252 will ramp the output by sourcing soft-
start limited current into the load capacitance. If the soft-
start voltage is below 1.2V, the circuit breaker TIMER is
held low. Above 1.2V, TIMER ramps up. It is important to
set the timer delay so that, regardless of which start-up
mode is used, the TIMER ramp is less than one circuit
breaker delay time. If this condition is not met, the
LTC4252-1 may shut down after one circuit breaker delay
time whereas the LTC4252-2 may continue to autoretry.
Board Removal
If the board is withdrawn from the card cage, the UV/OV
divider is the first to lose connection. This shuts off the
MOSFET and commutates the flow of current in the
connector. When the power pins subsequently separate,
there is no arcing.
Current Control
Three levels of protection handle short-circuit and over-
load conditions. Load current is monitored by SENSE and
resistor R
S
. There are three distinct thresholds at SENSE:
50mV for a timed circuit breaker function; 100mV for an
analog current limit loop; and 200mV for a fast, feedforward
comparator which limits peak current in the event of a
catastrophic short-circuit.
If, owing to an output overload, the voltage drop across R
S
exceeds 50mV, TIMER sources 230
μ
A into C
T
. C
T
eventu-
ally charges to a 4V threshold and the LTC4252 shuts off.
If the overload goes away before C
T
reaches 4V and SENSE
measures less than 50mV, C
T
slowly discharges (5.8
μ
A).
In this way the LTC4252’s circuit breaker function re-
sponds to low duty cycle overloads and accounts for fast
heating and slow cooling characteristics of the MOSFET.
Higher overloads are handled by an analog current limit
loop. If the drop across R
S
reaches 100mV, the current
limiting loop servos the MOSFET gate and maintains a
constant output current of 100mV/R
S
. In current limit
mode, V
OUT
typically rises and this increases MOSFET
heating. If V
OUT
> V
DRNCL
(7V), connecting an external
resistor, R
D
, between V
OUT
and DRAIN allows the fault
timing cycle to be shortened by accelerating the charging
of the TIMER capacitor. The TIMER pull-up current is
increased by 8 I
DRN
. Note that because SENSE > 50mV,
TIMER charges C
T
during this time and the LTC4252 will
eventually shut down.
Low impedance failures on the load side of the LTC4252
coupled with 48V or more driving potential can produce
current slew rates well in excess of 50A/
μ
s. Under these
conditions, overshoot is inevitable. A fast SENSE com-
parator with a threshold of 200mV detects overshoot and
pulls GATE low much harder and hence much faster than
the weaker current limit loop. The 100mV/R
S
current limit
loop then takes over and servos the current as previously
described. As before, TIMER runs and shuts down the
LTC4252 when C
T
reaches 4V.
If C
T
reaches 4V, the LTC4252-1 latches off with a 5.8
μ
A
pull-up current source whereas the LTC4252-2 starts a
shutdown cooling cycle. The LTC4252-1 circuit breaker
latch is reset by either pulling UV momentarily low or drop-
ping the input voltage V
IN
below the internal UVLO thresh-
old of 8.2V or pulling TIMER momentarily low with a switch.
The LTC4252-2 retries after its shutdown cooling cycle.
Although short-circuits are the most obvious fault type,
several operating conditions may invoke overcurrent pro-
tection. Noise spikes from the backplane or load, input
steps caused by the connection of a second, higher
voltage supply, transient currents caused by faults on
adjacent circuit boards sharing the same power bus or the
insertion of non-hot-swappable products could cause
higher than anticipated input current and temporary de-
tection of an overcurrent condition. The action of TIMER
and C
T
rejects these events allowing the LTC4252 to “ride
out” temporary overloads and disturbances that could trip
a simple current comparator and, in some cases, blow a
fuse.
相關(guān)PDF資料
PDF描述
LTC4252 Negative 48V Hot Swap Controller
LTC4252-1CMS TRANS ARRAY PNP/PNP SS MINI-6P
LTC4252-1CMS8 TRANS ARRAY NPN/NPN SSMINI-6
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC4252-1_12 制造商:LINER 制造商全稱:Linear Technology 功能描述:Negative Voltage Hot Swap Controllers
LTC4252-1A 制造商:LINER 制造商全稱:Linear Technology 功能描述:Negative Voltage Diode-OR Controller
LTC42521CMS 制造商:Linear Technology 功能描述:
LTC4252-1CMS 功能描述:IC CNTRLR HOTSWAP NEGVOLT 10MSOP RoHS:否 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
LTC4252-1CMS#PBF 功能描述:IC CNTRLR HOTSWAP NEGVOLT 10MSOP 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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