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参数资料
| 型号： | LM5046MHX |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封装： | TSSOP-28 |
| 文件页数： | 9/32页 |
| 文件大小： | 888K |
| 代理商： | LM5046MHX |
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Soft-Start of the Synchronous
Rectifiers
In addition to the basic soft-start already described, the
LM5046 contains a second soft-start function that gradually
turns on the synchronous rectifiers to their steady-state duty
cycle. This function keeps the synchronous rectifiers off dur-
ing the basic soft-start allowing a linear start-up of the output
voltage even into pre-biased loads. Then the SR output duty
cycle is gradually increased to prevent output voltage distur-
bances due to the difference in the voltage drop between the
body diode and the channel resistance of the synchronous
MOSFETs. Initially, when bias is supplied to the LM5046, the
SSSR capacitor is discharged by an internal MOSFET. When
the SS capacitor reaches a 2V threshold and once it is es-
tablished that COMP is in control of the duty cycle i.e. I
COMP
< 800A, the SSSR discharge is released and SSSR capac-
itor begins charging with a 20A current source. During the
soft-start of synchronous rectifiers, SR1 and SR2 are turned
on simultaneously in pairs, as shown in Figure 6(a), to avoid
any transformer imbalance. The duty cycle of the SR outputs
gradually increase with increasing SSSR voltage until the du-
ty cycle gets locked into the steady state value as shown in
Figure 6(b). The synchronous rectifier outputs can be dis-
abled by grounding the SSSR pin.
30147832
FIGURE 6. (a) Waveforms during Soft-Start
(b) Waveforms after Soft-Start
Pre-Bias Startup
A common requirement for power converters is to have a
monotonic output voltage start-up into a pre-biased load i.e.
a pre-charged output capacitor. In a pre-biased load condi-
tion, if the synchronous rectifiers are engaged prematurely
they will sink current from the pre-charged output capacitors
resulting in an undesired output voltage dip. This condition is
undesirable and could potentially damage the power convert-
er. The LM5046 utilizes unique control circuitry to ensure
intelligent turn-on of the synchronous rectifiers such that the
output has a monotonic startup. Initially, the SSSR capacitor
is held at ground to disable the synchronous MOSFETs al-
lowing the body diode to conduct. The synchronous rectifier
soft-start is initiated once it is established the duty cycle is
controlled by the COMP instead of the soft-start capacitor i.e.
I
COMP < 800A and the voltage at the SS pin>2V. The SSSR
capacitor is then released and is charged by a 20A current
source. Further, as shown in Figure 7, a 1V offset on the
SSSR pin is used to provide additional delay. This delay en-
sures the output voltage is in regulation avoiding any reverse
current when the synchronous MOSFETs are engaged.
Soft-Stop
As shown in Figure 8, if the UVLO pin voltage falls below the
1.25V standby threshold, but above the 0.4V shutdown
threshold, the SSSR capacitor is soft-stopped with a 60A
current source (3 times the charging current). Once the SSSR
pin reaches the 1.0V threshold, both the SS and SSSR pins
are immediately discharged to GND. Soft-stopping the power
converter gradually winds down the energy in the output ca-
pacitors and results in a monotonic decay of the output volt-
age. During the hiccup mode, the same sequence is executed
except that the SSSR is discharged with a 120A current
source (6 times the charging current). In case of an OVP, VCC
UV, thermal limit or a VREF UV condition, the power converter
hard-stops, whereby all of the control outputs are driven to a
low state immediately.
17
www.national.com
LM5046
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM5046MHX/NOPB | 功能描述:电流型 PWM 控制器 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 |
| LM5046SQ | 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 |
| 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 |
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