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参数资料
| 型号： | LTC3873ETS8#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK TSOT23-8 |
| 标准包装： | 500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 240kHz |
| 占空比： | 84% |
| 电源电压： | 8.8 V ~ 75 V |
| 降压： | 无 |
| 升压： | 是 |
| 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： | SOT-23-8 薄型，TSOT-23-8 |
| 包装： | 带卷 (TR) |
LTC3873
APPLICATIONS INFORMATION
The circuit in Figure 6 shows a third way to power the
LTC3873. An external series pre-regulator consisting of
series pass transistor Q1, zener diode D1 and bias resis-
tor R B brings V CC to at least 7.6V nominal, well above
the maximum rated V CC turn-off threshold of 4V. Resistor
R START momentarily charges the V CC node up to the V CC
turn-on threshold, enabling the LTC3873.
ringing on the SW pin disrupts the tiny slope compensa-
tion current out of the pin. It is not recommended to add
external slope compensation in this case.
Output Voltage Programming
The output voltage is set by a resistor divider according
to the following formula:
V O = 1 . 2 V ? ? 1 +
R B
V IN
Q1
R START
LTC3873
?
?
R 2 ?
R 1 ? ?
D1
8.2V
C VCC
0.1μF
V CC
GND
The external resistor divider is connected to the output
as shown in Figure 5, allowing remote voltage sensing.
3873 F06
Figure 6
Slope Compensation
The LTC3873 has built-in internal slope compensation to
stabilize the control loop against sub-harmonic oscillation.
It also provides the ability to externally increase slope
compensation by injecting a ramping current out of its SW
pin into an external slope compensation resistor (R SL in
Figure 5). This current ramp starts at zero right after the
NGATE pin has been set high. The current rises linearly
towards a peak of 20μA at the maximum duty cycle of
80%, shutting off once the NGATE pin goes low. A series
resistor (R SL ) connecting the SW pin to the current sense
resistor (R SENSE ) thus develops a ramping voltage drop.
From the perspective of the SW pin, this ramping voltage
adds to the voltage across the sense resistor, effectively
reducing the current comparator threshold in proportion
to duty cycle. The amount of reduction in the current
comparator threshold ( Δ V SENSE ) can be calculated using
the following equation:
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 24k or less.
Transformer Design Considerations
Transformer speci?cation and design is perhaps the
most critical part of applying the LTC3873 successfully.
In addition to the usual list of caveats dealing with high
frequency 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 a transformer turns ratio to suit a given ap-
plication. Simple ratios of small integers, e.g., 1:1, 2:1, 3:2,
etc. can be employed which yield more freedom in setting
total turns and mutual inductance. Simple integer turns
ratios also facilitate the use of “off-the-shelf” con?gurable
Δ V SENSE =
Duty Cycle – 6%
8 0 %
20 μ A ? R SLOPE
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
Note the external programmable slope compensation is
only needed when the internal slope compensation is not
suf?cient. In most applications R SL can be shorted. For the
LTC3873, when the R DS(ON) sensing technique is used, the
windings in series on the primary and three windings in
parallel on the secondary, a 3:1 turns ratio will be achieved.
Turns ratio can be chosen on the basis of desired duty
cycle. However, remember that the input supply voltage
3873fa
10
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LTC3873IDDB-5#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Isolated, Cut Tape No Rsense Constant Frequency Current Mode Boost/Flyb |
| LTC3873IDDB-5#TRMPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 8-DFN 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) |
| LTC3873IDDB-5#TRPBF | 功能描述:IC REG CTRLR BST FLYBK PWM 8-DFN 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) |
| LTC3873ITS8-5#PBF | 制造商:Linear Technology 功能描述:DP-SWREG/Isolated, Cut Tape No Rsense Constant Frequency Current Mode Boost/Flyb |
| LTC3873ITS8-5#TRMPBF | 功能描述:IC REG CTRLR BST FLYBK TSOT23-8 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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