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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： | 5/28页 |
| 文件大小： | 610K |
| 代理商： | LM5045MHX |
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at 2.0V and the external pulse amplitude should lift the pin to
between 3.5V and 5.0V on the low-to-high transition. The
synchronization pulse width should be between 15 and
200ns. The RT resistor is always required, whether the oscil-
lator is free running or externally synchronized and the SYNC
frequency must be equal to, or greater than the frequency set
by the RT resistor. When syncing to an external clock, it is
recommended to add slope compensation by connecting an
appropriate resistor from the VCC pin to the CS pin. Also dis-
able the SLOPE pin by grounding it.
Cycle-by-Cycle Current Limit
The CS pin is to be driven by a signal representative of the
transformer’s primary current. If the voltage on the CS pin ex-
ceeds 0.75V, the current sense comparator immediately ter-
minates the PWM cycle. A small RC filter connected to the
CS pin and located near the controller is recommended to
suppress noise. An internal 18
MOSFET discharges the ex-
ternal current sense filter capacitor at the conclusion of every
cycle. The discharge MOSFET remains on for an additional
40ns after the start of a new PWM cycle to blank leading edge
spikes. The current sense comparator is very fast and may
respond to short duration noise pulses. Layout is critical for
the current sense filter and the sense resistor. The capacitor
associated with CS filter must be placed very close to the de-
vice and connected directly to the CS and AGND pins. If a
current sense transformer is used, both the leads of the trans-
former secondary should be routed to the filter network, which
should be located close to the IC. When designing with a cur-
rent sense resistor, all of the noise sensitive low power ground
connections should be connected together near the AGND
pin, and a single connection should be made to the power
ground (sense resistor ground point).
Hiccup Mode
The LM5045 provides a current limit restart timer to disable
the controller outputs and force a delayed restart (i.e. Hiccup
mode) if a current limit condition is repeatedly sensed. The
number of cycle-by-cycle current limit events required to trig-
ger the restart is programmed by the external capacitor at the
RES pin. During each PWM cycle, the LM5045 either sources
or sinks current from the RES capacitor. If current limit is de-
tected, the 5
μA current sink is disabled and a 30μA current
source is enabled. If the RES voltage reaches the 1.0V
threshold, the following restart sequence occurs, as shown in
Figure 2:
The SS and SSSR capacitors are fully discharged
The 30
μA current source is turned-off and the 10μA
current source is turned-on.
Once the voltage at the RES pin reaches 4.0V the 10
μA
current source is turned-off and a 5
μA current sink is
turned-on, ramping the voltage on the RES capacitor
down to 2.0V.
Once RES capacitor reaches 2.0V, threshold, the 10
μA
current source is turned-on again. The RES capacitor
voltage is ramped between 4.0V and 2.0V eight times.
When the counter reaches eight, the RES pin voltage is
pulled low and the soft-start capacitor is released to begin
a soft-start sequence. The SS capacitor voltage slowly
increases. When the SS voltage reaches 1.0V, the PWM
comparator will produce the first narrow pulse.
If the overload condition persists after restart, cycle-by-
cycle current limiting will begin to increase the voltage on
the RES capacitor again, repeating the hiccup mode
sequence.
If the overload condition no longer exists after restart, the
RES pin will be held at ground by the 5
μA current sink and
the normal operation resumes.
The hiccup mode function can be completely disabled by
connecting the RES pin to the AGND pin. In this configuration
the cycle-by-cycle protection will limit the maximum output
current indefinitely, no hiccup restart sequences will occur.
30145416
FIGURE 2. Hiccup Mode Delay and Soft-Start Timing Diagram
13
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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