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| 型号： | LM5020SD-2/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 8/17页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK INV 10LLP |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1MHz |
| 占空比： | 50% |
| 电源电压： | 13 V ~ 90 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 是 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 10-WDFN 裸露焊盘 |
| 包装： | 标准包装 |
| 其它名称： | LM5020SD-2DKR |
SNVS275F – MAY 2004 – REVISED APRIL 2006
Current Limit/Current Sense
The LM5020 provides a cycle-by-cycle over current protection function. Current limit is accomplished by an
internal current sense comparator. If the voltage at the current sense comparator input exceeds 0.5V, the output
is immediately terminated. A small RC filter, located near the controller, is recommended to filter noise from the
current sense signal. The CS input has an internal MOSFET which discharges the CS pin capacitance at the
conclusion of every cycle. The discharge device remains on an additional 50ns after the beginning of the new
cycle to attenuate the leading edge spike on the current sense signal.
The LM5020 current sense and PWM comparators are very fast, and may respond to short duration noise
pulses. Layout considerations are critical for the current sense filter and sense resistor. The capacitor associated
with the CS filter must be located very close to the LM5020 and connected directly to the pins of the controller
(CS and GND). If a current sense transformer is used, both leads of the transformer secondary should be routed
to the sense resistor and the current sense filter network. A sense resistor located in the source of the primary
power MOSFET may be used for current sensing, but a low inductance resistor is required. When designing with
a current sense resistor all of the noise sensitive low power ground connections should be connected together
local to the controller and a single connection should be made to the high current power ground (sense resistor
ground point).
Oscillator and Sync Capability
A single external resistor connected between the RT and GND pins sets the LM5020 oscillator frequency.
Internal to the LM5020-2 device (50% duty cycle limited option) is an oscillator divide by two circuit. This divide
by two circuit creates an exact 50% duty cycle pulse which is used internally to create a precise 50% duty cycle
limit function. Because of this, the internal oscillator actually operates at twice the frequency of the output (OUT).
For the LM5020-1 device the oscillator frequency and the operational output frequency are the same. To set a
desired output operational frequency (F), the RT resistor can be calculated from:
LM5020-1:
1
RT =
F x 158 x 10 -12
(1)
LM5020-2:
RT =
1
F x 316 x 10 -12
(2)
The LM5020 can also be synchronized to an external clock. The external clock must have a higher frequency
than the free running oscillator frequency set by the RT resistor. The clock signal should be capacitively coupled
into the RT pin through a 100pF capacitor. A peak voltage level greater than 3.7 Volts at the RT pin is required
for detection of the sync pulse. The sync pulse width should be set between 15 to 150ns by the external
components. The RT resistor is always required, whether the oscillator is free running or externally synchronized.
The voltage at the RT pin is internally regulated at 2 Volts. The RT resistor should be located very close to the
device and connected directly to the pins of the controller (RT and GND).
PWM Comparator / Slope Compensation
The PWM comparator compares the current ramp signal with the loop error voltage derived from the error
amplifier output. The error amplifier output voltage at the COMP pin is offset by 1.4V and then further attenuated
by a 3:1 resistor divider. The PWM comparator polarity is such that 0 Volts on the COMP pin will result in a zero
duty cycle at the controller output. For duty cycles greater than 50 percent, current mode control circuits are
subject to sub-harmonic oscillation. By adding an additional fixed slope voltage ramp signal (slope compensation)
to the current sense signal, this oscillation can be avoided. The LM5020-1 integrates this slope compensation by
summing a current ramp generated by the oscillator with the current sense signal. Additional slope compensation
may be added by increasing the source impedance of the current sense signal. Since the LM5020-2 is not
capable of duty cycles greater than 50%, there is no slope compensation feature in this device.
8
Product Folder Links: LM5020
Copyright ? 2004–2006, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM5020SDX-1 | 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 |
| LM5020SDX-1/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 |
| LM5020SDX-2 | 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 |
| LM5020SDX-2/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 |
| LM5021 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:AC-DC Current Mode PWM Controller |
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