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參數(shù)資料
| 型號： | LTC4251CS6 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 電源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO6 |
| 封裝： | 1 MM HEIGHT, PLASTIC, MO-193, TSOT-23, 6 PIN |
| 文件頁數(shù)： | 5/20頁 |
| 文件大小： | 235K |
| 代理商： | LTC4251CS6 |
LTC4251/LTC4251-1/
LTC4251-2
13
425112fa
APPLICATIO S I FOR ATIO
WU
UU
capacitors. If LTC4251, LTC4251-1 or LTC4251-2s are
used throughout, they respond by limiting the inrush cur-
rent to a value of 100mV/RS. If CT is sized correctly, the
capacitors will recharge long before CT times out.
where 40mV represents the guaranteed minimum circuit
breaker threshold.
During the initial charging process, the LTC4251/
LTC4251-1/LTC4251-2 may operate the MOSFET in cur-
rent limit, forcing 80mV to 120mV across RS. The mini-
mum inrush current is given by:
I
mV
R
INRUSH MIN
S
()=
80
(4)
Maximum short-circuit current limit is calculated using
maximum VSENSE, or:
I
mV
R
SHORT CIRCUIT MAX
S
=
()
120
(5)
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:
t
CV
I
CV
I
CL CHARGE
L
SUPPLY MAX
INRUSH MIN
==
()
(6)
Substituting Equation (4) for IINRUSH(MIN) and equating
(6) with (2) gives:
C
CV
R
A
VmV
T
L
SUPPLY MAX
S
=
(
)
()
230
480
(7)
Returning to Equation (2), the TIMER period is calculated
and used in conjunction with VSUPPLY(MAX) and
ISHORT-CIRCUIT(MAX) to check the SOA curves of a prospec-
tive MOSFET.
As a numerical design example, consider a 30W load,
which requires 1A input current at 36V. If VSUPPLY(MAX) =
72V and CL = 100F, Equation (3) gives RSENSE = 40m;
Equation (7) gives CT = 207nF. To account for errors in
RSENSE, CT, TIMER current (230A) and TIMER threshold
(4V), the calculated value should be multiplied by 1.5,
giving a nearest standard value of CT = 330nF.
If a short-circuit occurs, a current of up to 120mV/40m
= 3A will flow in the MOSFET for 5.7ms as dictated by
GATE
10V/DIV
SENSE
200mV/DIV
–48RTN
50V/DIV
TIMER
5V/DIV
425112 F04
SUPPLY RING
OWING
TO CURRENT
OVERSHOOT
SUPPLY RING
OWING TO
MOSFET
TURN-OFF
ONSET OF OUTPUT
SHORT-CIRCUIT
FAST CURRENT
LIMIT
ANALOG
CURRENT LIMIT
CTIMER RAMP
LATCH OFF
TRACE 1
TRACE 2
TRACE 3
TRACE 4
2ms/DIV
Figure 4. Output Short-Circuit Behavior
(All Waveforms are Referenced to VEE)
MOSFET SELECTION
The external MOSFET switch must have adequate safe
operating area (SOA) to charge the load capacitance on
start-up and handle short-circuit conditions until TIMER
latchoff. These considerations take precedence over DC
current ratings. A MOSFET with adequate SOA for a given
application can always handle the required current, but the
oppositecannotbesaid.Consultthemanufacturer’sMOSFET
data sheet for safe operating area and effective transient
thermal impedance curves.
MOSFET selection is a three-step process. 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
load capacitance, IL and CL. The circuit breaker current trip
point (50mV/RS) should be set to accommodate the maxi-
mum load current. Note that maximum input current to a
DC/DC converter is expected at VSUPPLY (MIN). RS is given
by:
R
mV
I
S
L MAX
=
40
()
(3)
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| LTC4251CS6#PBF | 制造商:Linear Technology 功能描述:Hot Swap Controller 1-CH 6-Pin TSOT-23 |
| LTC4251CS6#TR | 功能描述:IC CTRLR HOTSWAP NEGVOLT SOT23-6 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(yīng)商設(shè)備封裝:10-MSOP 包裝:管件 |
| LTC4251CS6#TRM | 功能描述:IC CTRLR HOTSWAP NEGVOLT SOT23-6 RoHS:否 類別:集成電路 (IC) >> PMIC - 熱交換 系列:- 產(chǎn)品培訓(xùn)模塊:Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:100 系列:- 類型:熱插拔開關(guān) 應(yīng)用:通用 內(nèi)部開關(guān):是 電流限制:可調(diào) 電源電壓:9 V ~ 13.2 V 工作溫度:-40°C ~ 150°C 安裝類型:表面貼裝 封裝/外殼:10-WFDFN 裸露焊盤 供應(yīng)商設(shè)備封裝:10-TDFN-EP（3x3） 包裝:管件 |
| LTC4251CS6#TRMPBF | 功能描述:IC CTRLR HOTSWAP NEGVOLT SOT23-6 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(yīng)商設(shè)備封裝:10-MSOP 包裝:管件 |
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