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參數(shù)資料
| 型號： | RC5051M |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Current-Mode SMPS Controller |
| 中文描述： | SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO20 |
| 封裝： | SOIC-20 |
| 文件頁數(shù)： | 11/16頁 |
| 文件大小： | 141K |
| 代理商： | RC5051M |
PRODUCT SPECIFICATION
RC5051
REV. 1.0.4 4/2/01
11
developed across the sense resistor exceeds the 120mV com-
parator threshold voltage, the RC5051 reduces the output
duty cycle to help protect the power devices. The DC-DC
converter returns to normal operation after the fault has been
removed.
Oscillator
The RC5051 oscillator section uses a fixed current capacitor
charging configuration. An external capacitor (CEXT) is
used to set the oscillator frequency between 80KHz and
1MHz. This scheme allows maximum flexibility in choosing
external components.
In general, a higher operating frequency decreases the peak
ripple current flowing in the output inductor, thus allowing
the use of a smaller inductor value. In addition, operation at
higher frequencies decreases the amount of energy storage
that must be provided by the bulk output capacitors during
load transients due to faster loop response of the controller.
Unfortunately, the efficiency losses due to switching of the
MOSFETs increase as the operating frequency is increased.
Thus, efficiency is optimized at lower frequencies. An oper-
ating frequency of 300KHz is a typical choice which opti-
mizes efficiency and minimizes component size while
maintaining excellent regulation and transient performance
under all operating conditions.
Design Considerations and Component
Selection
Additional information on design and component selection
may be found in Fairchild Semiconductor’s Application
Note 53.
MOSFET Selection
This application requires N-channel Logic Level Enhance-
ment Mode Field Effect Transistors. Desired characteristics
are as follows:
Low Static Drain-Source On-Resistance,
R
DS,ON
< 20m
(lower is better)
Low gate drive voltage, V
GS
= 4.5V rated
Power package with low Thermal Resistance
Drain-Source voltage rating > 15V.
The on-resistance (R
DS,ON
) is the primary parameter for
MOSFET selection. The on-resistance determines the power
dissipation within the MOSFET and therefore significantly
affects the efficiency of the DC-DC Converter. For details
and a spreadsheet on MOSFET selection, refer to Applica-
tions Bulletin AB-8
MOSFET Gate Bias
The high side MOSFET gate driver can be biased by one of
two methods–Charge Pump or 12V Gate Bias. The charge
pump method has the advantage of requiring only +5V as an
input voltage to the converter, but the 12V method will real-
ize increased efficiency by providing an increased V
GS
to the
high side MOSFETs.
Method 1. Charge Pump (Bootstrap)
Figure 3 shows the use of a charge pump to provide gate bias
to the high side MOSFET when +12V is unavailable. Capac-
itor CP is the charge pump used to boost the voltage of the
RC5051 output driver. When the MOSFET Q1 switches off,
the source of the MOSFET is at approximately 0V because
of the MOSFET Q2. (The Schottky D2 conducts for only a
very short time, and is not relevent to this discussion.) CP is
charged through the Schottky diode D1 to approximately
4.5V. When the MOSFET Q1 turns on, the voltage at the
source of the MOSFET is equal to 5V. The capacitor voltage
follows, and hence provides a voltage at VCCQP equal to
almost 10V. The Schottky diode D1 is required to provide
the charge path when the MOSFET is off, and reverses
biases when VCCQP goes to 10V. The charge pump capaci-
tor (CP) needs to be a high Q, high frequency capacitor. A
1
μ
F ceramic capacitor is recommended here.
Figure 3. Charge Pump Configuration
Method 2. 12V Gate Bias
Figure 4 illustrates how a 12V source can be used to bias
VCCQP. A 47
resistor is used to limit the transient current
into the VCCQP pin and a 1μF capacitor is used to filter the
VCCQP supply. This method provides a higher gate bias
voltage (V
GS
) to the high side MOSFET than the charge
pump method, and therefore reduces the R
DS,ON
and the
resulting power loss within the MOSFET. In designs where
efficiency is a primary concern, the 12V gate bias method is
recommended. A 6.2V Zener diode, D1, is used to clamp the
voltage at VCCQP to a maximum of 12V and ensure that the
absolute maximum voltage of the IC will not be exceeded.
PWM/PFM
Control
65-5051-06
VO
+5V
D1
D2
CP
Q1
Q2
L2
RS
C
OUT
VCCQP
HIDRV
LODRV
GNDP
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| RC5051M_32 | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 DC-DC Converter Prog Sync RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| RC5051MT | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 Prog Sync DC-DC Low Voltage UPS RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| RC5051MT_32 | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 Prog Sync DC-DC Low Voltage UPS RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| RC5052 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| RC5052AH WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
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