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参数资料
| 型号： | LT3748EMS#TRPBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO12 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16/12 |
| 文件页数： | 2/30页 |
| 文件大小： | 284K |
| 代理商： | LT3748EMS#TRPBF |
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LT3748
10
3748fa
APPLICATIONS INFORMATION
Selecting Actual RREF, RFB and RTC Resistor Values
The preceding equations define how the LT3748 would
regulate the output voltage if the system had no time de-
lays and no error sources. However, there are a number of
repeatable delays and parasitics in each application which
will affect the output voltage and force a re-evaluation of
the RFBandRTCcomponentvalues.Thefollowingapproach
is the best method for selecting the correct values.
The expression for VOUT, developed in the Operation sec-
tion, can be rearranged to yield the following expression
for RFB:
R FB =
RREF NPS VOUT + VF
() + VTC
VBG
where:
VOUT = Output voltage
VF = Output diode forward voltage
NPS = Effective primary-to-secondary turns ratio
VTC = 0.55V
The equation assumes the temperature coefficients of the
output diode and VTC are equal and substitutes RFB/NPS for
the value of RTC. This is a good first order approximation
but will be revisited later.
First, the value of RREF should be approximately 6.04k
since the LT3748 is trimmed and specified using this
value. If the impedance of RREF varies considerably from
6.04k, additional errors will result. However, a variation in
RREF of several percent is acceptable. This yields a bit of
freedom in selecting standard 1% resistor values to yield
nominal RFB/RREF ratios.
With starting values for RFB and RTC, an initial iteration
of the application should be built with final selections of
all external components (transformer, diode, MOSFET,
etc.). The resulting VOUT should be measured and used
to re-evaluate the value of RFB due to non-idealities in the
sampling system:
RFB(NEW) =
VOUT(DESIRED)
VOUT(MEASURED)
RFB(OLD)
With a new value of RFB selected, the temperature co-
efficient of the output diode in the application can be
tested to verify the nominal RTC value. The RTC resistor
should be removed from the circuit under test (this will
cause VOUT to increase for this step) and VOUT should
be measured over temperature at a desired target output
load. It is very important for this evaluation that uniform
temperature be applied to both the output diode and the
LT3748—if freeze spray or a heat gun is used there can
be a significant mismatch in temperature between the
two devices that causes significant error. Attempting to
extrapolate the data from a diode datasheet or assuming
the nominal RTC value may yield a better result if there is
no method to apply uniform heat or cooling such as an
oven. With at least two data points (although more data
points from hot to cold are recommended), the change
in V/°C can be determined by:
ΔVOUT
ΔTEMP
=
VOUT1 –VOUT2
TEMP1– TEMP2
Using the measured VOUT temperature coefficient, an exact
RTC value can be selected using the following equation:
RTC =
RFB
NPS
1.85mV/°C
ΔVOUT
ΔTEMP
If the value of RTC has changed significantly, which can
happen with the use of some output diodes that have
a very low forward drop, the RFB value may need to be
changed to restore VOUT to the desired value. As in the
previous iteration, after measuring VOUT, a new RFB can
once again be selected using:
RFB(NEW) =
VOUT(DESIRED)
VOUT(MEASURED)
RFB(OLD)
Once the values of RFB and RTC are selected, the regulation
accuracy from board to board for a given application will
be very consistent, typically under ±5% when including
device variation of all the components in the system
(assuming resistor tolerances and transformer windings
matching of 1% or better). However, if the transformer,
the output diode or MOSFET switch are changed or the
layout is dramatically altered, there may be some change
in VOUT.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3748HMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
| LT3748HMS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LT3748HMSPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748HMSTRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748IMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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