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参数资料
| 型号： | LM5045MHX |
| 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： | ETSSOP-28 |
| 文件页数： | 11/28页 |
| 文件大小： | 610K |
| 代理商： | LM5045MHX |
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Table 1: Soft-Stop in Fault
Conditions
Fault Condition
SSSR
UVLO
(UVLO<1.25V)
Soft-Stop
3x the charging rate
OVP
(OVP>1.25V)
Hard-Stop
Hiccup
(CS>0.75 and RES>1V)
Soft-Stop
6x the charging rate
VCC/VREF UV
Hard-Stop
Internal Thermal Limit
Hard-Stop
Note: All the above conditions are valid with SSOFF pin tied
to GND. If SSOFF=5V, the LM5045 hard-stops in all the con-
ditions. The SS pin remains high in all the conditions until the
SSSR pin reaches 1V.
Thermal Protection
Internal thermal shutdown circuitry is provided to protect the
integrated circuit in the event the maximum rated junction
temperature is exceeded. When activated, typically at 160°C,
the controller is forced into a shutdown state with the output
drivers, the bias regulators (VCC and REF) disabled. This
helps to prevent catastrophic failures from accidental device
overheating. During thermal shutdown, the SS and SSSR ca-
pacitors are fully discharged and the controller follows a nor-
mal start-up sequence after the junction temperature falls to
the operating level (140 °C).
Applications Information
CONTROL METHOD SELECTION
The LM5045 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
full-bridge topology. The full-bridge topology, like other dou-
ble 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 causes 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 rep-
resentative of the primary current is compared against an
error signal to control the duty cycle. In steady-state, this re-
sults 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 LM5045
To configure the LM5045 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 9. 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.
30145424
FIGURE 9. Feed-Forward Voltage Mode Configuration
19
www.national.com
LM5045
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM5045MHX/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 |
| LM5045SQ | 制造商:TI 制造商全称:Texas Instruments 功能描述:Full-Bridge PWM Controller with Integrated MOSFET Drivers |
| LM5045SQ/NOPB | 功能描述:电流型 PWM 控制器 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 |
| LM5045SQX | 制造商:TI 制造商全称:Texas Instruments 功能描述:Full-Bridge PWM Controller with Integrated MOSFET Drivers |
| LM5045SQX/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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