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| 型号： | LTC4253ACGN#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | -48V Hot Swap Controller with Sequencer; Package: SSOP; No of Pins: 16; Temperature Range: 0°C to +70°C |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO16 |
| 封装： | 0.150 INCH, LEAD FREE, PLASTIC, SSOP-16 |
| 文件页数： | 13/34页 |
| 文件大小： | 369K |
| 代理商： | LTC4253ACGN#PBF |
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LTC4253/LTC4253A
20
425353afd
MOSFET SELECTION
The external MOSFET switch must have adequate safe op-
erating area (SOA) to handle short-circuit conditions until
TIMER times out. These considerations take precedence
over DC current ratings. A MOSFET with adequate SOA for
a given application can always handle the required current
buttheoppositemaynotbetrue.Consultthemanufacturer’s
MOSFET data sheet for safe operating area and effective
transient thermal impedance curves.
MOSFET selection is a 3-step process by assuming the
absence of soft-start capacitor. First, RS 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, IL and CL. The circuit breaker cur-
rent trip point (VCB/RS) should be set to accommodate
the maximum load current. Note that maximum input
current to a DC/DC converter is expected at VSUPPLY(MIN).
RS is given by:
RS =
VCB(MIN)
IL(MAX)
(8)
where VCB(MIN) = 40mV (45mV for the LTC4253A) repre-
sents the guaranteed minimum circuit breaker threshold.
Duringtheinitialchargingprocess,theLTC4253/LTC4253A
may operate the MOSFET in current limit, forcing (VACL)
between 80mV to 120mV (VACL is 54mV to 66mV for the
LTC4253A) across RS. The minimum inrush current is
given by:
IINRUSH(MIN) =
VACL(MIN)
RS
(9)
Maximum short-circuit current limit is calculated using
the maximum VSENSE. This gives
ISHORTCIRCUIT(MAX) =
VACL(MAX)
RS
(10)
The TIMER capacitor CT 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 CT is calculated based on the maximum time it takes
the load capacitor to charge. That time is given by:
tCL(CHARGE) =
C V
I
=
CL VSUPPLY(MAX)
IINRUSH(MIN)
(11)
The maximum current flowing in the DRAIN pin is given by:
IDRN(MAX) =
VSUPPLY(MAX) VDRNCL
RD
(12)
Approximating a linear charging rate, IDRN drops from
IDRN(MAX) to zero, the IDRN component in Equation (3)
can be approximated with 0.5 IDRN(MAX). Rearranging
the equation, TIMER capacitor CT is given by:
CT =
tCL(CHARGE) (200A + 4IDRN(MAX))
4V
(13)
Returning to Equation (3), the TIMER period is calcu-
lated and used in conjunction with VSUPPLY(MAX) and
ISHORTCIRCUIT(MAX) to check the SOA curves of a prospec-
tive MOSFET.
As a numerical design example for the LTC4253, consider
a 30W load, which requires 1A input current at 36V. If
VSUPPLY(MAX) = 72V and CL = 100F, RD = 1MΩ, Equation
(8) gives RS=40mΩ; Equation (13) gives CT = 414nF.
To account for errors in RS, CT, TIMER current (200A),
TIMER threshold (4V), RD, DRAIN current multiplier and
DRAINvoltageclamp(VDRNCL),thecalculatedvalueshould
be multiplied by 1.5, giving the nearest standard value of
CT=680nF.
Ifashort-circuitoccurs,acurrentofupto120mV/40mΩ=3A
willflowintheMOSFETfor6.3msasdictatedbyCT=680nF
in Equation (3). The MOSFET must be selected based on
this criterion. The IRF530S can handle 100V and 3A for
10ms and is safe to use in this application.
applicaTions inForMaTion
相关PDF资料 |
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| LTC4253ACGN#TRPBF | -48V Hot Swap Controller with Sequencer; Package: SSOP; No of Pins: 16; Temperature Range: 0°C to +70°C |
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| LTC4253CGN#TRPBF | -48V Hot Swap Controller with Sequencer; Package: SSOP; No of Pins: 16; Temperature Range: 0°C to +70°C |
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| LTC4253ACUF-ADJ#PBF | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-CH 20-Pin QFN EP |
| LTC4253ACUF-ADJ#TRPBF | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-CH 20-Pin QFN EP T/R |
| LTC4253AIGN#PBF | 功能描述:IC HOT SWAP CONTRLR -48V 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:100 系列:- 类型:热插拔开关 应用:通用 内部开关:是 电流限制:可调 电源电压:9 V ~ 13.2 V 工作温度:-40°C ~ 150°C 安装类型:表面贴装 封装/外壳:10-WFDFN 裸露焊盘 供应商设备封装:10-TDFN-EP（3x3） 包装:管件 |
| LTC4253AIGN#TRPBF | 功能描述:IC HOT SWAP CONTRLR -48V 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:100 系列:- 类型:热插拔开关 应用:通用 内部开关:是 电流限制:可调 电源电压:9 V ~ 13.2 V 工作温度:-40°C ~ 150°C 安装类型:表面贴装 封装/外壳:10-WFDFN 裸露焊盘 供应商设备封装:10-TDFN-EP（3x3） 包装:管件 |
| LTC4253AIGN-ADJ | 制造商:LINER 制造商全称:Linear Technology 功能描述:-48V Hot Swap Controller with Sequencer |
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