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参数资料
| 型号： | 750108 |
| 厂商： | Wurth Electronics Inc |
| 文件页数： | 10/30页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL FOR LT3748 |
| 设计资源： | LT3748 Design Schematic/Tips |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，隔离 |
| 功率 - 输出： | 30W |
| 输出电压： | 12V |
| 电流 - 输出： | 2.5A |
| 输入电压： | 22 ~ 75 V |
| 稳压器拓扑结构： | 回扫 |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | LT3748 |
| 相关产品： | LT3748HMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748HMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748IMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#TRPBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP LT3748EMS#PBF-ND - IC REG CTRLR FLYBK ISO CM 16MSOP |
| 其它名称： | 732-3308 |
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LT3748
APPLICATIONS INFORMATION
Selecting Actual R REF , R FB and R TC 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 R FB and R TC component values. The following approach
is the best method for selecting the correct values.
The expression for V OUT, developed in the Operation sec-
tion, can be rearranged to yield the following expression
for R FB :
With a new value of R FB selected, the temperature co-
efficient of the output diode in the application can be
tested to verify the nominal R TC value. The R TC resistor
should be removed from the circuit under test (this will
cause V OUT to increase for this step) and V OUT 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
R FB =
where:
R REF ? N PS ?? ( V OUT + V F ) + V TC ??
V BG
the nominal R TC 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:
V OUT = Output voltage
V F = Output diode forward voltage
Δ V OUT
Δ TEMP
=
V OUT1 – V OUT2
TEMP1 – TEMP2
R TC = ?
N PS = Effective primary-to-secondary turns ratio
V TC = 0.55V
The equation assumes the temperature coefficients of the
output diode and V TC are equal and substitutes R FB /N PS for
the value of R TC . This is a good first order approximation
but will be revisited later.
First, the value of R REF should be approximately 6.04k
since the LT3748 is trimmed and specified using this
value. If the impedance of R REF varies considerably from
6.04k, additional errors will result. However, a variation in
R REF of several percent is acceptable. This yields a bit of
Using the measured V OUT temperature coefficient, an exact
R TC value can be selected using the following equation:
R FB 1.85mV/ ° C
N PS Δ V OUT
Δ TEMP
If the value of R TC has changed significantly, which can
happen with the use of some output diodes that have
a very low forward drop, the R FB value may need to be
changed to restore V OUT to the desired value. As in the
previous iteration, after measuring V OUT , a new R FB can
once again be selected using:
freedom in selecting standard 1% resistor values to yield
nominal R FB /R REF ratios.
R FB(NEW) =
V OUT(DESIRED)
V OUT(MEASURED)
? R FB(OLD)
With starting values for R FB and R TC , an initial iteration
of the application should be built with final selections of
all external components (transformer, diode, MOSFET,
etc.). The resulting V OUT should be measured and used
to re-evaluate the value of R FB due to non-idealities in the
sampling system:
V OUT(DESIRED)
R FB(NEW) = ? R FB(OLD)
V OUT(MEASURED)
Once the values of R FB and R TC 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 V OUT .
3748fa
10
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相关代理商/技术参数 |
参数描述 |
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| 750109 | 制造商:Pilz International 功能描述:CONTACT MODULE 3NO/1NC 24V 制造商:PILZ 功能描述:CONTACT MODULE, 3NO/1NC, 24V, 30OHM 制造商:PILZ 功能描述:CONTACT MODULE, 3NO/1NC, 24V, 30OHM; Coil Voltage VDC Nom:24V; Contact Current Max:6A; Contact Voltage AC Nom:240V; Contact Voltage DC Max:24V; Coil Resistance:30ohm; Contact Configuration:3PST-NO, SPST-NC; Average Power ;RoHS Compliant: Yes |
| 750-109 | 功能描述:安装硬件 CIRC-O-GIDE .75in Nylon Black 94V-0 RoHS:否 制造商:Harwin 类型:SMT Cable Clip 材料:Phosphor Bronze 安装孔大小: 长度:5 mm 外径: 内径: 厚度: 电镀:Tin 螺纹大小: |
| 75010BK002 | 制造商:Alpha Wire Company 功能描述:Cat5e cable 2 pair solid 105deg 152m |
| 75010-BK002 | 制造商:Alpha Wire 功能描述: |
| 75-010BP | 制造商:RAYHOME 功能描述:ST/STEEL SHIM 0.10X75X75 |
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