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参数资料
| 型号： | LTC3705EGN#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/20页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR OCP 16SSOP |
| 标准包装： | 100 |
| 输出隔离： | 隔离 |
| 输入电压： | 18 V ~ 80 V |
| 输出电压： | 11V |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-SSOP（0.154"，3.90mm 宽） |
| 供应商设备封装： | 16-SSOP |
| 包装： | 管件 |
LTC3705
OPERATIO
the volt-second limit circuit. The duty cycle is always
limited to 50% to ensure that the power transformer flux
always has time to reset before the start of the next cycle.
In an alternate application, the volt-second limit can be
used for open-loop regulation of the output against changes
in V IN .
Current Limit
Current limit for the LTC3705 is principally a safety feature
to protect the converter and is not part of a control
function. The current that flows in series through the top
switch, the transformer primary, and the bottom switch is
sensed by a resistor connected between the source of the
bottom switch and GND. If the voltage across this resistor
exceeds 300mV, the LTC3705 initiates a fault.
Bootstrap Refresh
The LTC3705 incorporates a unique bootstrap refresh
circuit to ensure that the bootstrap supply (BOOST) for the
top switch has adequate voltage for operation at low duty
cycles. Therefore, the LTC3705 does not require a
undervoltage lockout for the bootstrap supply and a po-
tential source of unexpected shutdowns is eliminated.
Voltage Feedforward
The LTC3705 uses voltage feedforward to properly modu-
late the duty cycle as a function of the input voltage. For
secondary-side control with the LTC3706, voltage
feedforward is used during start-up only. The duty cycle
APPLICATIO S I FOR ATIO
UVLO
The UVLO pin is connected to a resistive voltage divider
during start up is determined by comparison of the voltage
on the SSFLT pin to a 50% duty cycle triangle wave with
an amplitude of 2V. To implement voltage feedforward, the
charging current for the soft-start capacitor is reduced in
proportion to the input voltage. As a result, the initial rate
of rise of the converter output voltage is held approxi-
mately constant regardless of the input voltage. At some
point during start-up, the LTC3706 begins to switch the
pulse transformer and takes over the soft-start.
For operation with standalone primary-side control and
optoisolator feedback, voltage feedforward is used during
both start-up and normal operation. The duty cycle is
determined by using a 50% duty cycle triangle wave with
an amplitude equal to 66% of the voltage on the UVLO pin
which is, in turn, proportional to V IN . The charging current
for the soft-start capacitor is a constant 5.2 μ A. During
soft-start, the duty cycle is determined by comparing the
voltage on the SSFLT pin to the triangle wave. Soft-start is
concluded when the voltage on the SSFLT pin exceeds the
voltage on the FB/IN + pin. After the conclusion of soft-
start, the duty cycle is determined by comparison of the
voltage on the FB/IN + pin to the triangle wave.
Optoisolator Bias
When the LTC3705 is used in standalone primary-side
mode, feedback is provided by an optoisolator connected
to the FB/IN + pin. The LTC3705 has a built optoisolator
bias circuit which eliminates the need for external
components.
The LTC3705 also has 16mV of voltage hysteresis on the
UVLO pin so that the UVLO threshold for V IN falling is:
connected to V IN as shown in Figure 2. The voltage
threshold on the UVLO pin for V IN rising is 1.242V. To
introduce hysteresis, the LTC3705 draws 4.9 μ A from the
V IN ( UVLO , FALLING ) = ( 1 . 226 V )
R1 + R2
R 2
UVLO pin when V IN is rising. The hysteresis is therefore
user adjustable and depends on the value of R1. The UVLO
threshold for V IN rising is:
To implement external Run/Stop control, connect a small
NMOS to the UVLO pin as shown in Figure 2. Turning the
NMOS on grounds the UVLO pin and prevents the LTC3705
V IN ( UVLO , RISING ) = ( 1 . 242 V )
R1 + R2
R 2
+ R 1 ( 4 . 9 μ A )
from running.
3705fb
10
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| LTC3705IGN | 制造商:Linear Technology 功能描述:Forward Controller and Gate Driver 16-Pin SSOP N |
| LTC3705IGN#PBF | 功能描述:IC CTRLR OCP 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - AC-DC 转换器，离线开关 系列:- 标准包装:3,000 系列:- 输出隔离:隔离 频率范围:61kHz ~ 71kHz 输入电压:9.4 V ~ 28 V 输出电压:12V 功率（瓦特）:- 工作温度:-40°C ~ 125°C 封装/外壳:SC-74，SOT-457 供应商设备封装:6-TSOP 包装:带卷 (TR) |
| LTC3705IGN#TRPBF | 功能描述:IC CTRLR OCP 16SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - AC-DC 转换器，离线开关 系列:- 标准包装:3,000 系列:- 输出隔离:隔离 频率范围:61kHz ~ 71kHz 输入电压:9.4 V ~ 28 V 输出电压:12V 功率（瓦特）:- 工作温度:-40°C ~ 125°C 封装/外壳:SC-74，SOT-457 供应商设备封装:6-TSOP 包装:带卷 (TR) |
| LTC3706EGN#PBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
| LTC3706EGN#TRPBF | 功能描述:IC SECONDARY SIDE CTRLR 24SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 电源控制器，监视器 系列:PolyPhase® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:- 应用:多相控制器 输入电压:- 电源电压:9 V ~ 14 V 电流 - 电源:- 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:40-WFQFN 裸露焊盘 供应商设备封装:40-TQFN-EP（5x5） 包装:带卷 (TR) |
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