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參數(shù)資料
| 型號： | LTC4252-2CMS8 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | Negative Voltage Hot Swap Controllers |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 17/32頁 |
| 文件大小： | 327K |
| 代理商： | LTC4252-2CMS8 |
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LTC4252-1/LTC4252-2
17
425212f
TIMER commences charging C
T
(Trace 4) while the analog
current limit loop maintains the fault current at 100mV/R
S
,
which in this case is 5A (Trace 2). Note that the backplane
voltage (Trace 1) sags under load. Timer pull-up is accel-
erated by V
OUT
. When C
T
reaches 4V, GATE turns off,
PWRGD pulls high, the load current drops to zero and the
backplane rings up to over 100V. The positive peak is
usually limited by avalanche breakdown in the MOSFET
and can be further limited by adding a zener diode across
the input from –48V to –48RTN, such as Diodes Inc.
SMAT70A.
A low impedance short on one card may influence the
behavior of others sharing the same backplane. The initial
glitch and backplane sag as seen in Figure 5 Trace 1, can
rob charge from output capacitors on adjacent cards.
When the faulty card shuts down, current flows in to
refresh the capacitors. If LTC4252s are used by the other
cards, they respond by limiting the inrush current to a
value of 100mV/R
S
. If C
T
is sized correctly, the capacitors
will recharge long before C
T
times out.
POWER GOOD, PWRGD
PWRGD latches low if GATE charges up to within 2.8V of
V
IN
and DRAIN pulls below V
DRNL
during start-up. PWRGD
is reset in UVLO, in a UV condition or if C
T
charges up to
4V. An overvoltage condition has no effect on PWRGD
status. A 58
μ
A current pulls this pin high during reset. Due
to voltage transients between the power module and
PWRGD, optoisolation is recommended. This pin pro-
vides sufficent drive for an optocoupler.
MOSFET SELECTION
The external MOSFET switch must have adequate safe
operating area (SOA) to handle short-circuit conditions
until TIMER times out. These considerations take prece-
dence over DC current ratings. A MOSFET with adequate
SOA for a given application can always handle the required
current, but the opposite may not be true. Consult the
manufacturer’s MOSFET data sheet for safe operating area
and effective transient thermal impedance curves.
MOSFET selection is a 3-step process by assuming the
absense of a soft-start capacitor. First, R
S
is calculated and
then the time required to charge the load capacitance is
determined. This timing, along with the maximum short-
circuit current and maximum input voltage defines an
operating point that is checked against the MOSFET’s SOA
curve.
To begin a design, first specify the required load current
and Ioad capacitance, I
L
and C
L
. The circuit breaker
current trip point (V
CB
/R
S
) should be set to accommodate
the maximum load current. Note that maximum input
current to a DC/DC converter is expected at V
SUPPLY(MIN)
.
R
S
is given by:
V
I
L MAX
(
)
R
S
CB MIN
(
=
)
(8)
where V
CB(MIN)
= 40mV represents the guaranteed mini-
mum circuit breaker threshold.
During the initial charging process, the LTC4252 may
operate the MOSFET in current limit, forcing (V
ACL
) be-
tween 80mV to 120mV across R
S
. The minimum inrush
current is given by:
I
mV
R
S
INRUSH MIN
(
)
=
80
(9)
Maximum short-circuit current limit is calculated using
the maximum V
SENSE
. This gives
I
mV
R
S
SHORTCIRCUIT MAX
(
)
=
120
(10)
The TIMER capacitor C
T
must be selected based on the
slowest expected charging rate; otherwise TIMER might
time out before the load capacitor is fully charged. A value
for C
T
is calculated based on the maximum time it takes the
load capacitor to charge. That time is given by:
t
C V
I
C
V
I
CL CHARGE
(
L
SUPPLY MAX
INRUSH MIN
)
(
)
(
)
=
=
(11)
APPLICATIU
W
U
U
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LTC4252-2CMS8#PBF | 功能描述:IC CNTRLR HOTSWAP NEGVOLT 8-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 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） 供應商設(shè)備封裝:10-MSOP 包裝:管件 |
| LTC4252-2CMS8#TR | 功能描述:IC CNTRLR HOTSWAP NEGVOLT 8-MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 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） 供應商設(shè)備封裝:10-MSOP 包裝:管件 |
| LTC4252-2CMS8#TRPBF | 功能描述:IC CNTRLR HOTSWAP NEGVOLT 8-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 標準包裝:50 系列:- 類型:熱交換控制器 應用:-48V 遠程電力系統(tǒng)，AdvancedTCA ? 系統(tǒng)，高可用性 內(nèi)部開關(guān):無 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） 供應商設(shè)備封裝:10-MSOP 包裝:管件 |
| LTC4252-2CMS8PBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Negative Voltage Hot Swap Controllers |
| LTC4252-2CMS8TR | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Negative Voltage Hot Swap Controllers |
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