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參數(shù)資料
| 型號： | LM5046MHX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數(shù)： | 7/32頁 |
| 文件大?。?/td> | 888K |
| 代理商： | LM5046MHX |
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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 LM5046, 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 LM5046 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 sourcing 1.5A peak and sinking 2A peak. The low-side gate
drivers are powered directly by the VCC regulator. The HO1
and HO2 gate drivers are powered from a bootstrap capacitor
connected between BST1/BST2 and HS1/HS2 respectively.
An external 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 cor-
responding 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 LM5046 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.
Figure 4 illustrates the sequence of the LM5046 gate-drive
outputs. Initially, the diagonal HO1 and LO2 are turned-on to-
gether during the power transfer cycle, followed by the free-
wheel cycle, where HO1 and HO2 are kept on. In the
subsequent phase, the diagonal HO2 and LO1 are turned-on
together during the power transfer cycle, followed by a free-
wheel cycle, where LO1 and LO2 are kept on. The power
transfer mode is often called the active mode and the free-
wheel mode is often called as the passive mode. The dead-
time between the passive mode and the active mode, T
PA, is
set by the RD1 resistor and the dead-time between the active
mode and the passive mode, T
AP, is set by the RD2 resistor.
Refer to the Applications Information section for more details
on the operation of the phase-shifted full-bridge topology.
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, T
PA is the time set by the RD1 resistor and FOSC is the
frequency of the oscillator. For example, if the oscillator fre-
quency is set at 400 kHz and the T
PA time set by the RD1
resistor is 60ns, the resulting D
MAX will be equal to 0.488.
30147821
FIGURE 4. Timing Diagram Illustrating the Sequence of Gate-Driver Outputs in the PSFB Topology
15
www.national.com
LM5046
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM5046MHX/NOPB | 功能描述:電流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| LM5046SQ | 制造商:TI 制造商全稱:Texas Instruments 功能描述:LM5046 Phase-Shifted Full-Bridge PWM Controller with Integrated MOSFET Drivers |
| LM5046SQ/NOPB | 功能描述:電流型 PWM 控制器 Phase-Shifted Full- Bridge PWM Cntrlr RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| LM5046SQX | 制造商:TI 制造商全稱: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 類別:集成電路 (IC) >> PMIC - AC-DC 轉換器，離線開關 系列:PowerWise® 標準包裝:1 系列:FPS™ 輸出隔離:隔離 頻率范圍:61kHz ~ 73kHz 輸入電壓:8 V ~ 26 V 輸出電壓:650V 功率（瓦特）:12W 工作溫度:-40°C ~ 115°C 封裝/外殼:8-DIP（0.300"，7.62mm） 供應商設備封裝:8-MDIP 包裝:Digi-Reel® 其它名稱:FSL206MRBNFSDKR |
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