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参数资料
| 型号： | LTC3873ETS8-5#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16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： | 4 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) |
LTC3873-5
APPLICATIONS INFORMATION
V CC Bias Power
The V CC pin must be bypassed to the GND pin with a
minimum 10μF ceramic or tantalum capacitor located
immediately adjacent to the two pins. Proper supply by-
passing is necessary to supply the high transient currents
required by the MOSFET gate driver.
For maximum ?exibility, the LTC3873-5 is designed so
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:
that it can be operated from voltages well beyond the
LTC3873-5’s absolute maximum ratings. In the simplest
case, the LTC3873-5 can be powered with a resistor con-
Δ V SENSE =
Duty Cycle – 6%
8 0 %
20 μ A ? R SLOPE
nected between the input voltage and V CC . The built-in shunt
regulator limits the voltage on the V CC pin to around 9.3V
as long as the shunt regulator is not forced to sink more
than 25mA. This powering scheme has the drawback that
the power loss in the resistor reduces converter ef?ciency
and the 25mA shunt regulator maximum may limit the
maximum-minimum range of input voltage.
The circuit in Figure 5 shows a second way to power the
LTC3873-5. 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
undervoltage lockout threshold.
Note the external programmable slope compensation is
only needed when the internal slope compensation is not
suf?cient. In some applications R SL can be shorted. For
the LTC3873-5, when the R DS(ON) sensing technique is
used, the ringing on the SW pin disrupts the tiny slope
compensation 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 +
V IN
?
?
R 2 ?
R 1 ? ?
R B
Q1
LTC3873-5
V CC
The external resistor divider is connected to the output
D1
8.2V
C VCC
0.1μF
GND
as shown in Figure 4, allowing remote voltage sensing.
Choose resistance values for R1 and R2 to be as large as
38735 F05
Figure 5. External Pre-Regulator for V CC Bias Power
Slope Compensation
The LTC3873-5 has built-in internal slope compensation
to stabilize the control loop against sub-harmonic oscilla-
tion. 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 2). This current ramp starts at zero right after
the NGATE pin has been high. The current rises linearly
towards a peak of 20μA at the maximum duty cycle of
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 LTC3873-5 successfully. In
addition to the usual list of caveats dealing with high fre-
quency power transformer design, the following should
prove useful.
80%, shutting off once the NGATE pin goes low. A series
38735fb
9
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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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