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参数资料
| 型号： | LM5046SQ |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, QCC28 |
| 封装： | 5 X 5 MM, LLP-28 |
| 文件页数： | 8/32页 |
| 文件大小： | 888K |
| 代理商： | LM5046SQ |
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Synchronous Rectifier Control
Outputs (SR1 & SR2)
Synchronous rectification (SR) of the transformer secondary
provides higher efficiency, especially for low output voltage
converters, compared to the diode rectification. The reduction
of rectifier forward voltage drop (0.5V - 1.5V) to 10mV -
200mV VDS voltage for a MOSFET significantly reduces
rectification losses. In a typical application, the transformer
secondary winding is center tapped, with the output power
inductor in series with the center tap. The SR MOSFETs pro-
vide the ground path for the energized secondary winding and
the inductor current. From Figure 5 it can be seen that when
the HO1/LO2 diagonal is turned ON, power transfer is en-
abled from the primary. During this period, the SR1 MOSFET
is enabled and the SR2 MOSFET is turned-off. The sec-
ondary winding connected to the SR2 MOSFET drain is twice
the voltage of the center tap at this time. At the conclusion of
the HO1/LO2 pulse, the inductor current continues to flow
through the SR2 MOSFET body diode. Since the body diode
causes more loss than the SR MOSFET, efficiency can be
improved by minimizing the T
SRON period. In the LM5046, the
time T
SRON is internally fixed to be 30ns. The 30ns internally
fixed dead-time, along with inherent system delays due to
galvanic isolation, plus the gate drive ICs, will provide suffi-
cient margin to prevent the shoot-through current.
During the freewheeling period, the inductor current flows in
both the SR1 and SR2 MOSFETs, which effectively shorts the
transformer secondary. The SR MOSFETs are disabled at the
rising edge of the CLK, which also disables HO1 or LO1. As
shown in Figure 5, SR1 is disabled at the same instant as HO1
is disabled, and SR2 is disabled at the same instant as LO1
is disabled. The dead-times, T
SROFF and TPA achieve two dif-
ferent things but are set by single resistor, RD1. Therefore,
RD1 value should be selected such that the SR1/SR2 turns-
off before the next power transfer cycle is initiated by T
PA.
The SR drivers are powered by the REF regulator and each
SR output is capable of sourcing 0.1A and sinking 0.4A peak.
The amplitude of the SR drivers is limited to 5V. The 5V SR
signals enable the LM5046 to transfer SR control across the
isolation barrier either through a solid-state isolator or a pulse
transformer. The actual gate sourcing and sinking currents for
the synchronous MOSFETs are provided by the secondary-
side bias and gate drivers.
T
PA and TAP can be programmed by connecting a resistor be-
tween RD1 and RD2 pins and AGND. It should be noted that
while RD1 effects the maximum duty cycle, RD2 does not.
The RD1 and RD2 resistors should be located very close to
the device. The formula for RD1 and RD2 resistors are given
below:
If the desired dead-time for T
PA is 60ns, then the RD1 will be
20 k
.
30147836
FIGURE 5. Synchronous Rectifier Timing Diagram
www.national.com
16
LM5046
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM5046SQ/NOPB | 功能描述:电流型 PWM 控制器 Phase-Shifted Full- Bridge PWM Cntrlr RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| LM5046SQX | 制造商:TI 制造商全称:Texas Instruments 功能描述:LM5046 Phase-Shifted Full-Bridge PWM Controller with Integrated MOSFET Drivers |
| LM5046SQX/NOPB | 功能描述:IC PWM CTRLR FULL BRIDG 28LLP RoHS:是 类别:集成电路 (IC) >> PMIC - AC-DC 转换器，离线开关 系列:PowerWise® 标准包装:1 系列:FPS™ 输出隔离:隔离 频率范围:61kHz ~ 73kHz 输入电压:8 V ~ 26 V 输出电压:650V 功率（瓦特）:12W 工作温度:-40°C ~ 115°C 封装/外壳:8-DIP（0.300"，7.62mm） 供应商设备封装:8-MDIP 包装:Digi-Reel® 其它名称:FSL206MRBNFSDKR |
| LM505 | 制造商:LM TECHNOLOGIES 功能描述:ADAPTER BLUETOOTH NANO EDR 40M USB 制造商:LM TECHNOLOGIES 功能描述:BLUETOOTH ADAPTER, USB, BCM2045, EDR 制造商:LM TECHNOLOGIES 功能描述:BLUETOOTH ADAPTER, USB, BCM2045, 40M, EDR; Data Rate:2.166Mbps; Operating Temperature Min:-20C; Operating Temperature Max:75C; Operating Frequency Range:2.402GHz to 2.48GHz; Operating Temperature Range:-20C to +75C ;RoHS Compliant: Yes |
| LM5050-1 | 制造商:TI 制造商全称:Texas Instruments 功能描述:High Side OR-ing FET Controller |
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