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参数资料
| 型号： | LTC3806EDE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBACK PWM 12-DFN |
| 标准包装： | 91 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 290kHz |
| 占空比： | 94% |
| 电源电压： | 10 V ~ 75 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 ~ 85°C |
| 封装/外壳： | 12-WFDFN 裸露焊盘 |
| 包装： | 管件 |
LTC3806
APPLICATIO S I FOR ATIO
3 . 3 V + ?
Some common secondary turns ratios:
V OUT
2.5
TURNS
3
D =
V OUT 1
V OUT 1 + ( N ? V IN )
=
3 . 3 V
? 48 V ?
? 15 ? ?
= 0 . 508
3.3
4
3.3
5.0
1.8
2
3
6
Input Power
The maximum input power is:
3.3
1.8
2.5
11
5
7
P IN =
∑ N K = 1 P OUTK
Eff
2.5
3.3
5.0
3
4
6
where P OUTK is the maximum power supplied by output K
and Eff represents the efficiency of the converter.
For example, assume we need a regulator that operates
with a nominal 48V input to produce one 3.3V output and
one 5V output. The ideal turns ratio for the 3.3V (master)
Continuing the previous example, assume OUT1 delivers
3.3V at 2A and OUT2 delivers 4.95V at 0.5A. For a
conversion efficiency at maximum output power of 80%:
N IDEAL1 =
= 0 . 06875
P IN =
output is:
3 .3
48
We select a turns ratio of 1/15 or N1 = 0.066…
3. 3 V ? 2 A + 4. 95 V ? 0. 5 A
0 . 80
Transformer Selection
= 11 . 34 W
For the 5V output, the ideal turns ratio is:
The transformer primary inductance, L P , is selected based
on the percentage peak-to-peak ripple current (X) in the
N IDEAL2 = N 1 ?
If we choose:
1
N2=
10
5
3 . 3
= 0 . 1010 ...
transformer relative to its maximum value. In general, X
should range from 20% to 40% ripple current (i.e., X = 0.2
to 0.4). Higher values of ripple will increase conduction
losses, while lower values will require larger cores.
Ripple current and percentage ripple will be largest at
and we assume OUT1 is exact, the voltage on slave
output 2 is:
minimum duty factor D, in other words at the highest input
voltage. L P can be calculated from:
V OUT2 = 3 . 3 ? 10 = 3 . 3 ? 1 . 5 = 4 . 95 V
f ? X MAX IN
1
1
L P =
V IN ( MAX ) 2 ? D MIN 2
? P
15
This does not include any other errors, so make sure that
the error in V OUT2 is only a fraction of what your specifica-
where f is nominally 250kHz.
Continuing the example, allow 40% maximum ripple at a
maximum input voltage of 72V:
3 . 3 V +
tion allows. When dealing with large numbers of outputs
trial and error is usually required to get reasonable turns
ratios on all outputs while keeping the errors (due to
imperfect turns ratios) low.
D MIN =
3 . 3 V
72 V
15
= 0 . 407
For the selected turns ratios, the duty factor for this design
with 48V input would be:
L P =
72 V 2 ? 0 . 407 2
2500 0 0 Hz ? 0 . 4 ? 11 . 34 W
= 757 μ H
3806fb
12
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