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| 型号： | LTC3803IS6-3#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK PWM TSOT23-6 |
| 标准包装： | 500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 330kHz |
| 占空比： | 90% |
| 电源电压： | 5.7 V ~ 8 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 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： | SOT-23-6 细型，TSOT-23-6 |
| 包装： | 带卷 (TR) |
| 相关产品： | 732-2263-6-ND - TRANS FLYBACK LTC3803 16.9UH 732-2263-1-ND - TRANS FLYBACK LTC3803 16.9UH 732-2263-2-ND - TRANS FLYBACK LTC3803 16.9UH |
LTC3803-3
APPLICATIONS INFORMATION
Many LTC3803-3 application circuits can be derived from
the topology shown in Figure 2.
The LTC3803-3 itself imposes no limits on allowed power
output, input voltage V IN or desired regulated output voltage
V OUT ; these are all determined by the ratings on the external
power components. The key factors are: Q1’s maximum
drain-source voltage (BV DSS ), on-resistance (R DS(ON) )
and maximum drain current, T1’s saturation ?ux level and
winding insulation breakdown voltages, C IN and C OUT ’s
maximum working voltage, ESR, and maximum ripple
current ratings, and D1 and R SENSE ’s power ratings.
T1
TRANSFORMER DESIGN CONSIDERATIONS
Transformer speci?cation and design is perhaps the most
critical part of applying the LTC3803-3 successfully. In
addition to the usual list of caveats dealing with high fre-
quency power transformer design, the following should
prove useful.
Turns Ratios
Due to the use of the external feedback resistor divider
ratio to set output voltage, the user has relative freedom
in selecting transformer turns ratio to suit a given appli-
cation. Simple ratios of small integers, e.g., 1:1, 2:1, 3:2,
etc. can be employed which yield more freedom in setting
D2
V IN
L BIAS
?
D1
total turns and mutual inductance. Simple integer turns
ratios also facilitate the use of “off-the-shelf” con?gu-
C VCC
R3
1
R START
5
V CC
I TH /RUN NGATE
C IN
6
L PRI
?
Q1
?
L SEC
C OUT
V OUT
rable transformers such as the Coiltronics VERSA-PAC?
series in applications with high input to output voltage
ratios. For example, if a 6-winding VERSA-PAC is used
with three windings in series on the primary and three
windings in parallel on the secondary, a 3:1 turns ratio
C C
2
LTC3803-3
GND SENSE
V FB
3
R1 R2
4
R SL
R SENSE
38033 F02
will be achieved.
Turns ratio can be chosen on the basis of desired duty
cycle. However, remember that the input supply voltage
plus the secondary-to-primary referred version of the
?yback pulse (including leakage spike) must not exceed
V OUT – 0 . 8 V
Figure 2. Typical LTC3803-3 Application Circuit
SELECTING FEEDBACK RESISTOR DIVIDER VALUES
The regulated output voltage is determined by the resistor
divider across V OUT (R1 and R2 in Figure 2). The ratio
of R2 to R1 needed to produce a desired V OUT can be
calculated:
R 2 = ? R 1
0 . 8 V
Choose resistance values for R1 and R2 to be as large as
possible in order to minimize any ef?ciency loss due to
the static current drawn from V OUT , but just small enough
so that when V OUT is in regulation, the error caused by
the nonzero input current to the V FB pin is less than 1%.
A good rule of thumb is to choose R1 to be 80k or less.
the allowed external MOSFET breakdown rating.
Leakage Inductance
Transformer leakage inductance (on either the primary
or secondary) causes a voltage spike to occur after the
output switch (Q1) turn-off. This is increasingly prominent
at higher load currents, where more stored energy must
be dissipated. In some cases a snubber circuit will be
required to avoid overvoltage breakdown at the MOSFET’s
drain node. Application Note 19 is a good reference on
snubber design.
A bi?lar or similar winding technique is a good way to
minimize troublesome leakage inductances. However,
remember that this will limit the primary-to-second-
ary breakdown voltage, so bi?lar winding is not always
practical.
38033fd
9
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| LTC3803IS6-5#TRPBF | 功能描述:IC REG CTRLR FLYBK PWM TSOT23-6 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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