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| 型号： | LTC4252A-2CMS#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 电源管理 |
| 英文描述： | Negative Voltage Hot Swap Controllers; Package: MSOP; No of Pins: 10; Temperature Range: 0°C to +70°C |
| 中文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO10 |
| 封装： | LEAD FREE, PLASTIC, MSOP-10 |
| 文件页数： | 13/36页 |
| 文件大小： | 394K |
| 代理商： | LTC4252A-2CMS#PBF |
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LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
20
425212fb
Approximating a linear charging rate as IDRN drops from
IDRN(MAX) to zero, the IDRN component in Equation (3) can
be approximated with 0.5 IDRN(MAX). Rearranging equa-
tion, TIMER capacitor CT is given by:
C
tA
I
V
T
CL CHARGE
DRN MAX
=
+
()
(
)
230
4
(13)
Returning to Equation (3), the TIMER period is calculated
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, consider a 30W load,
which requires 1A input current at 36V. If VSUPPLY(MAX) =
72V and CL = 100F, RD = 1M, Equation (8) gives RS =
40m
; Equation (13) gives CT = 441nF. To account for
errors in RS, CT, TIMER current (230A), TIMER threshold
(4V), RD, DRAIN current multiplier and DRAIN voltage
clamp (VDRNCL), the calculated value should be multiplied
by 1.5, giving the nearest standard value of CT = 680nF.
If a short-circuit occurs, a current of up to 120mV/
40m
= 3A will flow in the MOSFET for 5.6ms as dictated
by CT = 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.
Computing the maximum soft-start capacitor value during
soft-start to a load short is complicated by the nonlinear
MOSFET’s SOA characteristics and the RSSCSS response.
An overly conservative but simple approach begins with
the maximum circuit breaker current, given by:
I
V
R
CB MAX
S
()
=
(14)
where VCB(MAX) = 60mV (55mV for the LTC4252A).
From the SOA curves of a prospective MOSFET, determine
the time allowed, tSOA(MAX). CSS is given by:
C
t
R
SS
SOA MAX
SS
=
()
.
0 916
(15)
In the above example, 60mV/40m
gives 1.5A. tSOA(MAX)
for the IRF530S is 40ms. From Equation (15), CSS =
437nF. Actual board evaluation showed that CSS = 100nF
was appropriate. The ratio (RSS CSS) to tCL(CHARGE) is a
good gauge as a large ratio may result in the time-out
period expiring. This gauge is determined empirically with
board level evaluation.
SUMMARY OF DESIGN FLOW
To summarize the design flow, consider the application
shown in Figure 2 with the LTC4252A. It was designed for
80W.
Calculate the maximum load current: 80W/43V = 1.86A;
allowing for 83% converter efficiency, IIN(MAX) = 2.2A.
Calculate RS: from Equation (8) RS = 20m.
Calculate ISHORTCIRCUIT(MAX): from Equation (10)
I
mV
m
A
SHORTCIRCUIT MAX
()
.
=
=
66
20
33
Select a MOSFET that can handle 3.3A at 71V: IRF530S.
Calculate CT: from Equation (13) CT = 322nF. Select
CT = 680nF, which gives the circuit breaker time-out pe-
riod t = 5.6ms.
Consult MOSFET SOA curves: the IRF530S can handle
3.3A at 100V for 8.2ms, so it is safe to use in this
application.
Calculate CSS: using Equations (14) and (15) select
CSS = 68nF.
FREQUENCY COMPENSATION
The LTC4252A typical frequency compensation network
for the analog current limit loop is a series RC (10) and
CC connected to VEE. Figure 7 depicts the relationship
between the compensation capacitor CC and the MOSFET’s
CISS. The line in Figure 7 is used to select a starting value
for CC based upon the MOSFET’s CISS specification. Opti-
mized values for CC are shown for several popular
MOSFETs. Differences in the optimized value of CC versus
the starting value are small. Nevertheless, compensation
values should be verified by board level short-circuit
testing.
APPLICATIO S I FOR ATIO
WU
U
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4252A-2CMSTR | 制造商:LINER 制造商全称:Linear Technology 功能描述:Negative Voltage Hot Swap Controllers |
| LTC4252A-2CMSTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Negative Voltage Hot Swap Controllers |
| LTC4252A-2IMS | 功能描述:IC CTRLR HOTSWAP NEG VOLT 10MSOP RoHS:否 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 |
| LTC4252A-2IMS#PBF | 功能描述:IC CNTRLR HOTSWAP NEGVOLT 10MSOP 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 |
| LTC4252A-2IMS#TR | 功能描述:IC CTRLR HOTSWAP NEG VOLT 10MSOP RoHS:否 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 |
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