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| 型号： | LT3799IMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/20页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER TRIAC DIM 16-MSOP |
| 产品培训模块： | LT3799 Offline Isolated Flyback LED Controller |
| 标准包装： | 37 |
| 拓扑： | 交直流离线开关，反激式，PFC |
| 输出数： | 1 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 通用 |
| 频率： | 25kHz ~ 300kHz |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 供应商设备封装： | 16-MSOP，裸露焊盘 |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 125°C |
| 配用： | 732-2898-ND - IND TOROID LT3799 NCL30000 750UH |
LT3799
OPERATION
SECONDARY
DIODE CURRENT
I PK(sec)
voltage is 120Hz, so the control loop unity gain frequency
needs to be set less than approximately 120Hz. Without a
large amount of energy storage on the secondary side, the
output current is affected by the supply voltage changes,
but the DC component of the output current is accurate.
SWITCH
WAVEFORM
T FLYBACK
3799 F01
T PERIOD
Figure 1. Secondary Diode Current and Switch Waveforms
current and zero during the rest of the cycle. The equation
for expressing the output current is:
I OUT = 0.5 ? I PK ? N ? D′
where D′ is equal to the percentage of the cycle represented
by the flyback time.
The LT3799 has access to both the primary winding cur-
rent, the input to the current comparator, and when the
flyback time starts and ends. Now the output current can
be calculated by averaging a PWM waveform with the
height of the current limit and the duty cycle of the flyback
time over the entire cycle. In the feedback loop previously
described, the input to the integrator is such a waveform.
The integrator adjusts the peak current until the calculated
output current equals the control voltage. If the calculated
output current is low compared to the control pin, the error
amplifier increases the voltage on the COMP + node, thus
increasing the current comparator input.
When the V IN_SENSE voltage is connected to a resistor
divider of the supply voltage, the current limit is propor-
tional to the supply voltage if COMP + is held constant.
The output of the error amplifier is multiplied with the
V IN_SENSE pin voltage. If the LT3799 is configured with a
fast control loop, slower changes from the V IN_SENSE pin
will not interfere with the current limit or the output current.
The COMP + pin will adjust to the changes of the V IN_SENSE .
The only way for the multiplier to function properly is to
set the control loop to be an order of magnitude slower
than the fundamental frequency of the V IN_SENSE signal. In
the offline case, the fundamental frequency of the supply
TRIAC Dimming Features
The LT3799 incorporates some special features that aid in
the design of an offline LED current source when used with
a TRIAC dimmer. TRIAC dimmers are not ideal switches
when turned off and allow milliamps of current to flow
through them. This is an issue if used with a low quiescent
part such as the LT3799. Instead of turning the main power
MOSFET off when the TRIAC is off, this power device is
kept on and sinks the current to properly load the TRIAC.
When the TRIAC turns on, the V IN_SENSE pin detects this
and enables the loop, but the current comparator is always
enabled and turns the switch off if it is tripped.
Start-Up
The LT3799 uses a hysteretic start-up to operate from
high offline voltages. A resistor connected to the supply
voltage protects the part from high voltages. This resis-
tor is connected to the V IN pin on the part and also to a
capacitor. When the resistor charges the part up to 23V and
INTV CC is in regulation at 10V, the part begins to charge the
CT pin to 340mV and then starts to switch. The resistor
does not provide power for the part in steady state, but
relies on the capacitor to start-up the part, then the third
winding begins to provide power to the V IN pin along with
the resistor. An internal voltage clamp is attached to the
V IN pin to prevent the resistor current from allowing V IN
to go above the absolute maximum voltage of the pin.
The internal clamp is set at 25V and is capable of 28mA
(typical) of current at room temperature. But, ideally, the
resistor connected between the input supply and the V IN
pin should be chosen so that less than 10mA is being
shunted by this internal clamp.
CT Pin and Faults
The CT pin is a timing pin for the fault circuitry. When the
input voltages are at the correct levels, the CT pin sources
10μA of current. When the CT pin reaches 340mV, the part
3799fa
10
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| LT3800EFE#PBF | 功能描述:IC REG CTRLR INV PWM CM 16-TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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