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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： | 7/28页 |
| 文件大小： | 610K |
| 代理商： | LM5045MHX |
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Soft-Start
The soft-start circuit allows the power converter to gradually
reach a steady state operating point, thereby reducing the
start-up stresses and current surges. When bias is supplied
to the LM5045, the SS capacitor is discharged by an internal
MOSFET. When the UVLO, VCC and REF pins reach their
operating thresholds, the SS capacitor is released and is
charged with a 20A current source. Once the SS pin voltage
crosses the 1V offset, SS controls the duty cycle. The PWM
comparator is a three input device; it compares the RAMP
signal against the lower of the signals between the soft-start
and the loop error signal. In a typical isolated application, as
the secondary bias is established, the error amplifier on the
secondary side soft-starts and establishes closed- loop con-
trol, steering the control away from the SS pin.
One method to shutdown the regulator is to ground the SS
pin. This forces the internal PWM control signal to ground,
reducing the output duty cycle quickly to zero. Releasing the
SS pin begins a soft-start cycle and normal operation re-
sumes. A second shutdown method is presented in the UVLO
section.
Gate Driver Outputs
The LM5045 provides four gate drivers: two floating high side
gate drivers HO1 and HO2 and two ground referenced low
side gate drivers LO1 and LO2. Each internal driver is capable
of source 1.5A peak and sinking 2A peak. Initially, the diago-
nal HO1 and LO2 are turned-on together, followed by an off-
time when all the four gate driver outputs are off. In the
subsequent phase the diagonal HO2 and LO1 are turned on
together followed by an off-time. The low-side gate drivers are
powered directly by the VCC regulator. The HO1 and HO2
gate drivers are powered from a bootstrap capacitor connect-
ed between BST1/BST2 and HS1/HS2 respectively. An ex-
ternal diode connected between VCC (anode pin) and BST
(cathode pin) provides the high side gate driver power by
charging the bootstrap capacitor from VCC when the corre-
sponding switch node (HS1/HS2 pin) is low. When the high
side MOSFET is turned on, BST1 rises to a peak voltage
equal to VCC + V
HS1 where VHS1 is the switch node voltage.
The BST and VCC capacitors should be placed close to the
pins of the LM5045 to minimize voltage transients due to par-
asitic inductances since the peak current sourced to the MOS-
FET gates can exceed 1.5A. The recommended value of the
BST capacitor is 0.1
μF or greater. A low ESR / ESL capacitor,
such as a surface mount ceramic, should be used to prevent
voltage droop during the HO transitions.
If the COMP pin is open circuit, the outputs will operate at
maximum duty cycle. The maximum duty cycle for each
phase is limited by the dead-time set by the RD1 resistor. If
the RD1 resistor is set to zero then the maximum duty cycle
is slightly less than 50% due to the internally fixed dead-time.
The internally fixed dead-time is 30ns which does not vary
with the operating frequency. The maximum duty cycle for
each output can be calculated from the following equation:
Where, T1 is the time set by the RD1 resistor and F
OSC is the
frequency of the oscillator. For example, if the oscillator fre-
quency is set at 400 kHz and the T1 time set by the RD1
resistor is 60ns, the resulting D
MAX will be equal to 0.488.
30145421
FIGURE 4. Timing Diagram Illustrating the Maximum Duty Cycle and Dead-Time Set by RD1
15
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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