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参数资料
| 型号： | LT3837EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 18/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO 16-TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 88% |
| 电源电压： | 4.5 V ~ 20 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： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
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LT3837
APPLICATIONS INFORMATION
R PGDLY (k ? ) =
R ENDLY (k ? ) = ENDLY
t SS =
= 70ms ? C SFST (μF)
EnableDelayTime(ENDLY)
Enable delay time provides a programmable delay between
turn-off of the primary gate drive node and the subsequent
enabling of the feedback amplifier. As discussed earlier, this
delay allows the feedback amplifier to ignore the leakage
inductance voltage spike on the primary side.
The worst-case leakage spike pulse width is at maximum
load conditions. So set the enable delay time at these
conditions.
While the typical applications for this part use forced
continuous operation, it is conceivable that a secondary-
side controller might cause discontinuous operation at
light loads. 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. The enable delay time
should be made long enough to ignore the “irrelevant”
portion of the flyback waveform at light load.
Even though the LT3837 has a robust gate drive, the gate
transition-time slows with very large MOSFETs. Increase
delay time is as required when using such MOSFETs.
The enable delay resistor is set with the following equa-
tion:
t (ns) – 30
2.616
Keep R ENDLY greater than 40k. A good starting point
is 56k.
Primary Gate Delay Time (PGDLY)
Primary gate delay is the programmable time from the
turn-off of the synchronous MOSFET to the turn-on of
the primary side MOSFET. Correct setting eliminates
overlap between the primary side switch and secondary
side synchronous switch(es) and the subsequent current
spike in the transformer. This spike will cause additional
component stress and a loss in regulator efficiency.
The primary gate delay resistor is set with the following
equation:
t PGDLY (ns) + 47
9.01
A good starting point is 27k.
Soft-Start Functions
The LT3837 contains an optional soft-start function that is
enabled by connecting an external capacitor between the
SFST pin and ground. Internal circuitry prevents the control
voltage at the V C pin from exceeding that on the SFST pin.
There is an initial pull-up circuit to quickly bring the SFST
voltage to approximately 0.8V. From there it charges to
approximately 2.8V with a 20μA current source.
The SFST node is then discharged to 0.8V when a fault
occurs. A fault is V CC too low (undervoltage lockout),
current sense voltage greater than 200mV or the IC’s
thermal (overtemperature) shutdown is tripped. When
SFST discharges, the V C node voltage is also pulled low
to below the minimum current voltage. Once discharged,
the SFST recharges up again.
In this manner, switch currents are reduced and the stresses
in the converter are reduced during fault conditions.
The time it takes to fully charge soft-start is:
C SFST ? 1.4V
20μA
UVLO Pin Function
The UVLO pin provides a user programming undervoltage
lockout. This is usually used to provide undervoltage
lockout based on V IN . The gate drivers are disabled when
UVLO is below the 1.24V UVLO threshold. An external
resistive divider between the input supply and ground is
used to set the turn-on voltage.
The bias current on this pin depends on the pin volt-
age and UVLO state. The change provides the user with
adjustable UVLO hysteresis. When the pin rises above
the UVLO threshold a small current is sourced out of the
pin, increasing the voltage on the pin. As the pin voltage
drops below this threshold, the current is stopped, further
3837fd
18
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| LT3837IFE#PBF | 功能描述:IC REG CTRLR FLYBK ISO 16-TSSOP 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) |
| LT3837IFE#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO 16-TSSOP 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) |
| LT383L313 | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
| LT3844 | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage, Current Mode Switching Regulator Controller with Programmable Operating Frequency |
| LT3844EFE | 制造商:LINER 制造商全称:Linear Technology 功能描述:High Voltage, Current Mode Switching Regulator Controller with Programmable Operating Frequency |
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