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参数资料
| 型号： | LT1725CGN#TR |
| 厂商： | Linear Technology |
| 文件页数： | 15/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO CM 16SSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 125kHz |
| 占空比： | 90% |
| 电源电压： | 最高 22V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | 0°C ~ 100°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 相关产品： | 732-2262-6-ND - TRANS FLYBACK LT1725 20.4UH 732-2262-1-ND - TRANS FLYBACK LT1725 20.4UH 732-2262-2-ND - TRANS FLYBACK LT1725 20.4UH |
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LT1725
APPLICATIO S I FOR ATIO
to transformer leakage inductance. This spike is not in-
dicative of actual output voltage (see Figure 4B). Delaying
the enabling of the feedback amplifier allows this system
to effectively ignore most or all of the voltage spike and
maintain proper output voltage regulation. The enable
delay time should therefore be set to the maximum ex-
pected duration of the leakage spike. This may have
Minimum Enable Time
This function sets a minimum duration for the expected
flyback pulse. Its primary purpose is to provide a mini-
mum source current at the V C node to avoid start-up
problems.
Average “start-up” V C current =
implications regarding output voltage regulation at mini-
mum load (see Minimum Load Considerations).
A second benefit of the enable delay time function occurs
Minimum Enable Time
Switching Frequency
? I SRC
at light load. Under such conditions the amount of energy
stored in the transformer is small. The flyback waveform
becomes “lazy” and some time elapses before it indicates
the actual secondary output voltage (see Figure 4C). So
the enable delay time should also be set long enough to
ignore the “irrelevant” portion of the flyback waveform at
light load.
Additionally, there are cases wherein the gate output is
called upon to drive a large geometry MOSFET such that
the turnoff transition is slowed significantly. Under such
circumstances, the enable delay time may be increased to
accommodate for the lengthy transition.
MOSFET GATE DRIVE
Minimum enable time can also have implications at light
load (see Minimum Load Considerations). The temptation
is to set the minimum enable time to be fairly short, as this
is the least restrictive in terms of minimum load behavior.
However, to provide a “reliable” minimum start-up current
of say, nominally 1 μ A, the user should set the minimum
enable time at no less that 2% of the switching period
(= 1/switching frequency).
CURRENT SENSE RESISTOR CONSIDERATIONS
The external current sense resistor allows the user to
optimize the current limit behavior for the particular appli-
cation under consideration. As the current sense resistor
is varied from several ohms down to tens of milliohms,
peak switch current goes from a fraction of an ampere to
tens of amperes. Care must be taken to ensure proper
circuit operation, especially with small current sense
A
IDEALIZED FLYBACK
resistor values.
WAVEFORM
For example, a peak switch current of 10A requires a sense
resistor of 0.025 ? . Note that the instantaneous peak power
in the sense resistor is 2.5W, and it must be rated accord-
FLYBACK WAVEFORM
ingly. The LT1725 has only a single sense line to this re-
B
C
ENABLE
DELAY
TIME
NEEDED
ENABLE DELAY
TIME NEEDED
DISCONTINUOUS
MODE
RINGING
Figure 4
WITH LARGE LEAKAGE
SPIKE AT HEAVY LOAD
“SLOW” FLYBACK
WAVEFORM AT
LIGHT LOAD
1725 F04
sistor. Therefore, any parasitic resistance in the ground side
connection of the sense resistor will increase its apparent
value. In the case of a 0.025 ? sense resistor, one milliohm
of parasitic resistance will cause a 4% reduction in peak
switch current. So resistance of printed circuit copper
traces and vias cannot necessarily be ignored.
An additional consideration is parasitic inductance. Induc-
tance in series with the current sense resistor will accen-
tuate the high frequency components of the current
waveform. In particular, the gate switching spike and
multimegahertz ringing at the MOSFET can be considerably
1725fa
15
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1725CS | 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC RoHS:否 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) |
| LT1725CS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC 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) |
| LT1725CS#TR | 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC RoHS:否 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) |
| LT1725CS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16SOIC 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) |
| LT1725IGN | 功能描述:IC REG CTRLR FLYBK ISO CM 16SSOP RoHS:否 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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