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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： | 14/32页 |
| 文件大小： | 888K |
| 代理商： | LM5046MHX |
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CONTROL METHOD SELECTION
The LM5046 is a versatile PWM control IC that can be con-
figured for either current mode control or voltage mode con-
trol. The choice of the control method usually depends upon
the designer preference. The following must be taken into
consideration while selecting the control method. Current
mode control can inherently balance flux in both phases of the
PSFB topology. The PSFB topology, like other double ended
topologies, is susceptible to the transformer core saturation.
Any asymmetry in the volt-second product applied between
the two alternating phases results in flux imbalance that caus-
es a dc buildup in the transformer. This continual dc buildup
may eventually push the transformer into saturation. The volt-
second asymmetry can be corrected by employing current
mode control. In current mode control, a signal representative
of the primary current is compared against an error signal to
control the duty cycle. In steady-state, this results in each
phase being terminated at the same peak current by adjusting
the pulse-width and thus applying equal volt-seconds to both
the phases.
Current mode control can be susceptible to noise and sub-
harmonic oscillation, while voltage mode control employs a
larger ramp for PWM and is usually less susceptible. Voltage-
mode control with input line feed-forward also has excellent
line transient response. When configuring for voltage mode
control, a dc blocking capacitor can be placed in series with
the primary winding of the power transformer to avoid any flux
imbalance that may cause transformer core saturation.
VOLTAGE MODE CONTROL USING THE LM5046
To configure the LM5046 for voltage mode control, an exter-
nal resistor (R
FF) and capacitor (CFF) connected to VIN, AG-
ND, and the RAMP pins is required to create a saw-tooth
modulation ramp signal shown in Figure 11. The slope of the
signal at RAMP will vary in proportion to the input line voltage.
The varying slope provides line feed-forward information nec-
essary to improve line transient response with voltage mode
control. With a constant error signal, the on-time (T
ON) varies
inversely with the input voltage (VIN) to stabilize the Volt-
Second product of the transformer primary. Using a line feed-
forward ramp for PWM control requires very little change in
the voltage regulation loop to compensate for changes in in-
put voltage, as compared to a fixed slope oscillator ramp.
Furthermore, voltage mode control is less susceptible to
noise and does not require leading edge filtering. Therefore,
it is a good choice for wide input range power converters.
Voltage mode control requires a Type-III compensation net-
work, due to the complex-conjugate poles of the L-C output
filter.
30147824
FIGURE 11. Feed-Forward Voltage Mode Configuration
The recommended capacitor value range for C
FF is from
100pF to 1800pF. Referring to Figure 11, it can be seen that
C
FF value must be small enough to be discharged with in the
clock pulse-width which is typically within 50ns. The R
DS(ON)
of the internal discharge FET is 5.5
.
The value of R
FF required can be calculated from
For example, assuming a V
RAMP of 1.5V (a good compromise
of signal range and noise immunity), at VIN
MIN of 36V (oscil-
lator frequency of 400 kHz and C
FF = 470pF results in a value
for R
FF of 125 k.
CURRENT MODE CONTROL USING THE LM5046
The LM5046 can be configured for current mode control by
applying a signal proportional to the primary current to the
RAMP pin. One way to achieve this is shown in Figure 12.
The primary current can be sensed using a current trans-
former or sense resistor, the resulting signal is filtered and
applied to the RAMP pin through a resistor used for slope
compensation. It can be seen that the signal applied to the
RAMP pin consists of the primary current information from the
CS pin plus an additional ramp for slope compensation,
added by the resistor R
SLOPE.
The current sense resistor is selected such that during over
current condition, the voltage across the current sense resis-
tor is above the minimum CS threshold of 728mV.
21
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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