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| 型号： | LTC4268IDKD-1#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 39/46页 |
| 文件大小： | 419K |
| 描述： | IC PD HIGH POWER W/CNTRL 32-DFN |
| 标准包装： | 2,500 |
| 类型： | 以太网供电开关（PoE） |
| 应用： | 远程外设（工业控制，相机，数据访问） |
| 内部开关： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFDFN 裸露焊盘 |
| 供应商设备封装： | 32-DFN（7x4）裸露焊盘 |
| 包装： | 带卷 (TR) |
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LTC4268-1
39
With C
MILLER
determined, calculate the primary-side power
MOSFET power dissipation:
P
D(PRI)
=I
RMS(PRI)
2
R
DS(ON)
1+d
( )
+
V
IN(MAX)
P
IN(MAX)
DC
MIN
R
DR
C
MILLER
V
GATE(MAX)
V
TH
f
OSC
where:
R
DR
is the gate driver resistance (H10W)
V
TH
is the MOSFET gate threshold voltage
f
OSC
is the operating frequency
V
GATE(MAX)
= 7.5V for this part
(1 + d) is generally given for a MOSFET in the form of a
normalized R
DS(ON)
vs temperature curve. If you dont have
a curve, use d = 0.005/癈 " DT for low voltage MOSFETs.
The secondary-side power MOSFETs typically operate
at substantially lower V
DS
, so you can neglect transition
losses. The dissipation is calculated using:
P
DIS(SEC)
= I
RMS(SEC)
2
" R
DS(ON)
(1 + d)
With power dissipation known, the MOSFETs junction
temperatures are obtained from the equation:
T
J
= T
A
+ P
DIS
" ?/DIV>
JA
where T
A
is the ambient temperature and ?/DIV>
JA
is the MOSFET
junction to ambient thermal resistance.
Once you have T
J
iterate your calculations recomputing
d and power dissipations until convergence.
Gate Drive Node Consideration
The PG and SG gate drivers are strong drives to minimize
gate drive rise and fall times. This improves efficiency
but the high frequency components of these signals can
cause problems. Keep the traces short and wide to reduce
parasitic inductance.
The parasitic inductance creates an LC tank with the
MOSFET gate capacitance. In less than ideal layouts, a
series resistance of 5W or more may help to dampen the
ringing at the expense of slightly slower rise and fall times
and poorer efficiency.
The LTC4268-1 gate drives will clamp the max gate voltage
to roughly 7.5V, so you can safely use MOSFETs with
maximum V
GS
of 10V and larger.
Synchronous Gate Drive
There are several different ways to drive the synchronous
gate MOSFET. Full converter isolation requires the synchro-
nous gate drive to be isolated. This is usually accomplished
by way of a pulse transformer. Usually the pulse driver is
used to drive a buffer on the secondary as shown in the
application on the front page of this data sheet.
However, other schemes are possible. There are gate drivers
and secondary side synchronous controllers available that
provide the buffer function as well as additional features.
Capacitor Selection
In a flyback converter, the input and output current flows
in pulses, placing severe demands on the input and output
filter capacitors. The input and output filter capacitors are
selected based on RMS current ratings and ripple voltage.
Select an input capacitor with a ripple current rating
greater than:
I
RMS(PRI)
=
P
IN
V
IN(MIN)
1DC
MAX
DC
MAX
Continuing the example:
I
RMS(PRI)
=
29.5W
41V
1 49.4%
49.4%
=0.728A
Keep input capacitor series resistance (ESR) and
inductance (ESL) small, as they affect electromagnetic
interference suppression. In some instances, high ESR can
also produce stability problems because flyback converters
exhibit a negative input resistance characteristic. Refer
to Application Note 19 for more information. The output
capacitor is sized to handle the ripple current and to ensure
acceptable output voltage ripple.
applicaTions inForMaTion
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC4269-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at PD with Synchronous No-Opto Flyback Controller |
| LTC4269-2 | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at High Power PD and Synchronous Forward Controller with AUX Support |
| LTC4269CDKD-1#PBF | 功能描述:IC PD/OPTO FLYBACK CTRLR 32-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 热交换 系列:- 标准包装:50 系列:- 类型:热交换控制器 应用:-48V 远程电力系统，AdvancedTCA ? 系统，高可用性 内部开关:无 电流限制:可调 电源电压:11.5 V ~ 14.5 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽） 供应商设备封装:10-MSOP 包装:管件 |
| LTC4269CDKD-1#TRPBF | 功能描述:IC PD/OPTO FLYBACK CTRLR 32-DFN 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 |
| LTC4269CDKD-1-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:IEEE 802.3at PD with Synchronous No-Opto Flyback Controller |
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