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參數(shù)資料
| 型號： | LT3748HMS#PBF |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO12 |
| 封裝： | LEAD FREE, PLASTIC, MSOP-16/12 |
| 文件頁數(shù)： | 10/30頁 |
| 文件大?。?/td> | 284K |
| 代理商： | LT3748HMS#PBF |
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LT3748
18
3748fa
APPLICATIONS INFORMATION
Soft-Start
The LT3748 contains an optional soft-start function that
is enabled by connecting an explicit external capacitor
between the SS pin and ground. Internal circuitry prevents
the control voltage at the VC pin from exceeding that on
the SS pin.
The soft-start function is engaged whenever power at
VIN is removed, or as a result of either undervoltage
lockout, overcurrent in the sense resistor or thermal
(overtemperature) shutdown. The SS node is then
discharged to roughly 600mV. When this condition is
removed, a nominal 5μA current acts to charge up the SS
node towards roughly 2.2V. For example, a 0.1μF soft-start
capacitor will place a 0.05V/ms limit on the turn-on ramp
rate at the VC node.
ENABLE and Undervoltage Lockout (UVLO)
A resistive divider from VIN to the EN/UVLO pin implements
undervoltage lockout (UVLO). The EN/UVLO pin threshold
is set at 1.223V. In addition, the EN/UVLO pin draws 2.4μA
when the voltage at the pin is below 1.223V. This current
provides user programmable hysteresis based on the value
of R1. The effective UVLO thresholds are:
VIN(UVLO,RISING) =
1.223V (R1+ R2)
R2
+ 2.4μA R1
VIN(UVLO,FALLING) =
1.223V (R1+ R2)
R2
Figure 10 shows the implementation of external shutdown
control while still using the UVLO function. The NMOS
grounds the EN/UVLO pin when turned on, and puts the
LT3748 in shutdown with a quiescent current draw of
less than 1μA.
Minimum Load Requirement
The LT3748 recovers output voltage information using
the flyback pulse that occurs once the external MOSFET
turns off and the secondary winding conducts current. In
order to regulate the output voltage, the LT3748 needs to
sample the flyback pulse. The LT3748 delivers a minimum
amount of energy even during light load conditions to
ensure accurate output voltage information. The minimum
delivery of energy creates a minimum load requirement
on the output of approximately 2% of maximum load.
The minimum operating frequency at minimum load is
approximately 42kHz.
Alternatively, a Zener diode sufficiently rated to handle the
minimum load power can be used to provide a minimum
load without decreasing efficiency in normal operation. In
selecting a Zener diode for this purpose, the Zener voltage
should be high enough that the diode does not become the
load path during transient conditions but the voltage must
still be low enough that the MOSFET and output voltage
ratings are not exceeded when the Zener functions as the
minimum load.
INTVCC Pin Considerations
The INTVCC pin powers the internal circuitry and gate
driver of the LT3748. Three unique configurations exist
for regulation of the INTVCC pin as shown in Figure 11.
In the first configuration, the internal LDO drives the
INTVCC pin internally from the VIN supply. In the second
configuration, the VIN supply directly drives the INTVCC
pin through a direct connection bypassing the internal
LDO. Use this optional configuration for voltages lower
than 20V. In the third configuration, an external supply or
third winding drives the INTVCC pin. Use this option when
a voltage supply exists lower than the input supply but
higher than the regulated INTVCC voltage. Using a lower
voltage supply provides a more efficient source of power
for internal circuitry and reduces power dissipation in
the LT3748.
When calculating the minimum input voltage required for
a valid INTVCC, or the power dissipated in the LT3748, it is
useful to know how much current will be drawn from the
INTVCC LDO during normal operation. The easiest way to
calculate this current is to use the gate charge (QG) for the
LT3748
EN/UVLO
GND
R2
R1
VIN
3748 F10
RUN/STOP
CONTROL
(OPTIONAL)
Figure 10. Undervoltage Lockout (UVLO)
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LT3748HMSTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100V Isolated Flyback Controller |
| LT3748IMS#PBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMS#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO CM 16MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LT3748IMSPBF | 制造商:Linear Technology 功能描述:100V Isolated Flyback Controller MSOP16 |
| LT3748IMSTRPBF | 制造商:LINER 制造商全稱:Linear Technology 功能描述:100V Isolated Flyback Controller |
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