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參數(shù)資料
| 型號： | LM5035AMH-1 |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | SWITCHING CONTROLLER, 2000 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數(shù)： | 10/30頁 |
| 文件大小： | 585K |
| 代理商： | LM5035AMH-1 |
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FIGURE 5. HO, LO, SR1 and SR2 Timing Diagram
Synchronous Rectifier Control
Outputs (SR1 & SR2)
Synchronous rectification (SR) of the transformer secondary
provides higher efficiency, especially for low output voltage
converters. The reduction of rectifier forward voltage drop
(0.5V - 1.5V) to 10mV - 200mV V
DS voltage for a MOSFET
significantly reduces rectification losses. In a typical applica-
tion, the transformer secondary winding is center tapped, with
the output power inductor in series with the center tap. The
SR MOSFETs provide the ground path for the energized sec-
ondary winding and the inductor current. Figure 5 shows that
the SR2 MOSFET is conducting while HO enables power
transfer from the primary. The SR1 MOSFET must be dis-
abled during this period since the secondary winding con-
nected to the SR1 MOSFET drain is twice the voltage of the
center tap. At the conclusion of the HO pulse, the inductor
current continues to flow through the SR1 MOSFET body
diode. Since the body diode causes more loss than the SR
MOSFET, efficiency can be improved by minimizing the T2
period while maintaining sufficient timing margin over all con-
ditions (component tolerances, etc.) to prevent shoot-through
current. When LO enables power transfer from the primary,
the SR1 MOSFET is enabled and the SR2 MOSFET is off.
During the time that neither HO nor LO is active, the inductor
current is shared between both the SR1 and SR2 MOSFETs
which effectively shorts the transformer secondary and can-
cels the inductance in the windings. The SR2 MOSFET is
disabled before LO delivers power to the secondary to pre-
vent power being shunted to ground. The SR2 MOSFET body
diode continues to carry about half the inductor current until
the primary power raises the SR2 MOSFET drain voltage and
reverse biases the body diode. Ideally, dead-time T1 would
be set to the minimum time that allows the SR MOSFET to
turn off before the SR MOSFET body diode starts conducting.
The SR1 and SR2 outputs are powered directly by the VCC
regulator. Each output is capable of sourcing and sinking 0.5A
peak. Typically, the SR1 and SR2 signals control SR MOS-
FET gate drivers through a pulse transformer. The actual gate
sourcing and sinking currents are provided by the secondary-
side bias supply and gate drivers.
The timing of SR1 and SR2 with respect to HO and LO is
shown in Figure 5. SR1 is configured out of phase with HO
and SR2 is configured out of phase with LO. The deadtime
between transitions is programmable by a resistor connected
from the DLY pin to the AGND pin. Typically, R
DLY is set in
the range of 10k
to 100k. The deadtime periods can be
calculated using the following formulae:
T1 = .003 x R
DLY + 4.6 ns
T2 = .0007 x R
DLY + 10.01 ns
To set the minimum (propagation delays only) deadtime, the
DLY pin should be left open or connected to the REF pin. Any
resistor value above 300k
connected between the DLY pin
and AGND will also provide the minimum period (approxi-
mately 5 ns).
Thermal Protection
Internal Thermal Shutdown circuitry is provided to protect the
integrated circuit in the event the maximum rated junction
temperature is exceeded. When activated, typically at 165°C,
the controller is forced into a low power standby state with the
output drivers (HO, LO, SR1 and SR2), the bias regulators
(VCC and REF) disabled. This helps to prevent catastrophic
failures from accidental device overheating. During thermal
shutdown, the soft-start capacitor is fully discharged and the
controller follows a normal start-up sequence after the junc-
tion temperature falls to the operating level (145°C).
www.national.com
18
LM5035A/LM5035A-1
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| LM5035AMH-1/NOPB | 功能描述:電壓模式 PWM 控制器 100V Hb Pwm W/Driver RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
| LM5035AMHX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PWM Controller with Integrated Half-Bridge and SyncFET PWM Controller with Integrated Half-Bridge and SyncFET |
| LM5035AMHX/NOPB | 功能描述:電壓模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓?fù)浣Y(jié)構(gòu):Buck 輸出電壓:34 V 輸出電流: 開關(guān)頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel |
| LM5035AMHX-1 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:PWM Controller with Integrated Half-Bridge and SyncFET PWM Controller with Integrated Half-Bridge and SyncFET |
| LM5035AMHX-1/NOPB | 功能描述:板上安裝溫度傳感器 RoHS:否 制造商:Omron Electronics 輸出類型:Digital 配置: 準(zhǔn)確性:+/- 1.5 C, +/- 3 C 溫度閾值: 數(shù)字輸出 - 總線接口:2-Wire, I2C, SMBus 電源電壓-最大:5.5 V 電源電壓-最小:4.5 V 最大工作溫度:+ 50 C 最小工作溫度:0 C 關(guān)閉: 安裝風(fēng)格: 封裝 / 箱體: 設(shè)備功能:Temperature and Humidity Sensor |
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