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| 型号： | LT3573EMSE#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 1.85 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | LEAD FREE, PLASTIC, MSOP-16 |
| 文件页数： | 4/26页 |
| 文件大小： | 1182K |
| 代理商： | LT3573EMSE#PBF |
LT3573
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applications inForMation
Turns Ratio
Note that when using an RFB/RREF resistor ratio to set
output voltage, the user has relative freedom in selecting
a transformer turns ratio to suit a given application. In
contrast, simpler ratios of small integers, e.g., 1:1, 2:1,
3:2, etc., can be employed to provide more freedom in
setting total turns and mutual inductance.
Typically,thetransformerturnsratioischosentomaximize
availableoutputpower.Forlowoutputvoltages(3.3Vor5V),
aN:1turnsratiocanbeusedwithmultipleprimarywindings
relative to the secondary to maximize the transformer’s
current gain (and output power). However, remember that
the SW pin sees a voltage that is equal to the maximum
input supply voltage plus the output voltage multiplied by
the turns ratio. This quantity needs to remain below the
ABS MAX rating of the SW pin to prevent breakdown of
the internal power switch. Together these conditions place
an upper limit on the turns ratio, N, for a given application.
Choose a turns ratio low enough to ensure:
N
V V
V
IN MAX
OUT
F
<
+
50 –
(
)
For larger N:1 values, a transformer with a larger physical
size is needed to deliver additional current and provide a
largeenoughinductancevaluetoensurethattheoff-timeis
long enough to accurately measure the output voltage.
For lower output power levels, a 1:1 or 1:N transformer
can be chosen for the absolute smallest transformer size.
A 1:N transformer will minimize the magnetizing induc-
tance (and minimize size), but will also limit the available
output power. A higher 1:N turns ratio makes it possible
to have very high output voltages without exceeding the
breakdown voltage of the internal power switch.
Linear Technology has worked with several magnetic
componentmanufacturerstoproducepredesignedflyback
transformers for use with the LT3573. Table 5 shows the
details of several of these transformers.
Leakage Inductance
Transformer leakage inductance (on either the primary or
secondary) causes a voltage spike to appear at the primary
after the output switch turns off. This spike is increasingly
prominent at higher load currents where more stored
energy must be dissipated. In most cases, a snubber
circuit will be required to avoid overvoltage breakdown at
the output switch node. Transformer leakage inductance
should be minimized.
An RCD (resistor capacitor diode) clamp, shown in
Figure 4, is required for most designs to prevent the
leakage inductance spike from exceeding the breakdown
voltage of the power device. The flyback waveform is
depicted in Figure 5. In most applications, there will be a
very fast voltage spike caused by a slow clamp diode that
may not exceed 60V. Once the diode clamps, the leakage
inductance current is absorbed by the clamp capacitor.
This period should not last longer than 150ns so as not to
interfere with the output regulation, and the voltage during
this clamp period must not exceed 55V. The clamp diode
turns off after the leakage inductance energy is absorbed
and the switch voltage is then equal to:
VSW(MAX) = VIN(MAX) + N(VOUT + VF)
This voltage must not exceed 50V. This same equation
also determines the maximum turns ratio.
When choosing the snubber network diode, careful atten-
tion must be paid to maximum voltage seen by the SW
pin. Schottky diodes are typically the best choice to be
used in the snubber, but some PN diodes can be used if
they turn on fast enough to limit the leakage inductance
spike. The leakage spike must always be kept below 60V.
Figures 6 and 7 show the SW pin waveform for a 24VIN,
5VOUT application at a 1A load current. Notice that the
leakage spike is very high (more than 65V) with the “bad”
diode, while the “good” diode effectively limits the spike
to less than 55V.
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PDF描述 |
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| LT3573IMSE#TRPBF | 1.85 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, PDSO16 |
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| LT3581EMSE#PBF | SWITCHING REGULATOR, PDSO16 |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3573EMSETRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Isolated Flyback Converter without an Opto-Coupler |
| LT3573EMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Isolated Flyback Converter Without an Opto-Coupler |
| LT3573IMSE#PBF | 功能描述:IC REG FLYBACK ISO ADJ 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT3573IMSE#PBF | 制造商:Linear Technology 功能描述:DC-DC CONVERTER FLYBACK 1MHZ MSOP-16 制造商:Linear Technology 功能描述:DC-DC CONVERTER, FLYBACK, 1MHZ, MSOP-16 |
| LT3573IMSE#TRPBF | 功能描述:IC REG FLYBACK ISO ADJ 16MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
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