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參數(shù)資料
| 型號： | LM5046SQ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 540 kHz SWITCHING FREQ-MAX, QCC28 |
| 封裝： | 5 X 5 MM, LLP-28 |
| 文件頁數(shù)： | 14/32頁 |
| 文件大?。?/td> | 888K |
| 代理商： | LM5046SQ |
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CONTROL METHOD SELECTION
The LM5046 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
PSFB topology. The PSFB topology, like other double 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 caus-
es 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 representative
of the primary current is compared against an error signal to
control the duty cycle. In steady-state, this results 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 LM5046
To configure the LM5046 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 11. 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.
30147824
FIGURE 11. Feed-Forward Voltage Mode Configuration
The recommended capacitor value range for C
FF is from
100pF to 1800pF. Referring to Figure 11, it can be seen that
C
FF value must be small enough to be discharged with in the
clock pulse-width which is typically within 50ns. The R
DS(ON)
of the internal discharge FET is 5.5
.
The value of R
FF required can be calculated from
For example, assuming a V
RAMP of 1.5V (a good compromise
of signal range and noise immunity), at VIN
MIN of 36V (oscil-
lator frequency of 400 kHz and C
FF = 470pF results in a value
for R
FF of 125 k.
CURRENT MODE CONTROL USING THE LM5046
The LM5046 can be configured for current mode control by
applying a signal proportional to the primary current to the
RAMP pin. One way to achieve this is shown in Figure 12.
The primary current can be sensed using a current trans-
former or sense resistor, the resulting signal is filtered and
applied to the RAMP pin through a resistor used for slope
compensation. It can be seen that the signal applied to the
RAMP pin consists of the primary current information from the
CS pin plus an additional ramp for slope compensation,
added by the resistor R
SLOPE.
The current sense resistor is selected such that during over
current condition, the voltage across the current sense resis-
tor is above the minimum CS threshold of 728mV.
21
www.national.com
LM5046
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| 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(guān)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(zhuǎn)換器，離線開關(guān) 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 |
| LM505 | 制造商:LM TECHNOLOGIES 功能描述:ADAPTER BLUETOOTH NANO EDR 40M USB 制造商:LM TECHNOLOGIES 功能描述:BLUETOOTH ADAPTER, USB, BCM2045, EDR 制造商:LM TECHNOLOGIES 功能描述:BLUETOOTH ADAPTER, USB, BCM2045, 40M, EDR; Data Rate:2.166Mbps; Operating Temperature Min:-20C; Operating Temperature Max:75C; Operating Frequency Range:2.402GHz to 2.48GHz; Operating Temperature Range:-20C to +75C ;RoHS Compliant: Yes |
| LM5050-1 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:High Side OR-ing FET Controller |
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