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| 型号： | RC5057MT |
| 厂商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 中文描述： | SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | SOIC-16 |
| 文件页数： | 8/23页 |
| 文件大小： | 215K |
| 代理商： | RC5057MT |
RC5057
PRODUCT SPECIFICATION
16
REV. 1.2.0 2/10/00
has typical RDS,on rather than maximum, and is at 25°C. This
is the reason for using the external sense resistor.) At this point,
the internal comparator trips and signals the controller to
discharge the softstart capacitor. This causes a drastic reduc-
tion in the output voltage as the load regulation collapses
into the short circuit control mode. With a 40m
output
short, the voltage is reduced to 16.4A * 40m
= 650mV. The
output voltage does not return to its nominal value until the
output current is reduced to a value within the safe operating
range for the DC-DC converter.
Figure 6. Precision Current Sensing
Schottky Diode Selection
The application circuit of Figure 1 shows a Schottky diode,
D1, which is used as a free-wheeling diode to assure that the
body-diode in Q2 does not conduct when the upper MOS-
FET is turning off and the lower MOSFET is turning on. It is
undesirable for this diode to conduct because its high for-
ward voltage drop and long reverse recovery time degrades
efciency, and so the Schottky provides a shunt path for the
current. Since this time duration is very short, the selection
criterion for the diode is that the forward voltage of the
Schottky at the output current should be less than the for-
ward voltage of the MOSFET’s body diode.
Output Filter Capacitors
The output bulk capacitors of a converter help determine its
output ripple voltage and its transient response. It has already
been seen in the section on selecting an inductor that the ESR
helps set the minimum inductance, and the capacitance value
helps set the maximum inductance. For most converters,
however, the number of capacitors required is determined by
the transient response and the output ripple voltage, and these
are determined by the ESR and not the capacitance value. That
is, in order to achieve the necessary ESR to meet the transient
and ripple requirements, the capacitance value required is
already very large.
The most commonly used choice for output bulk capacitors
is aluminum electrolytics, because of their low cost and low
ESR. The only type of aluminum capacitor used should be
those that have an ESR rated at 100kHz. Consult Application
Bulletin AB-14 for detailed information on output capacitor
selection.
The output capacitance should also include a number of small
value ceramic capacitors placed as close as possible to the
processor; 0.1F and 0.01F are recommended values.
Input Filter
The DC-DC converter design may include an input inductor
between the system +5V supply and the converter input as
shown in Figure 7. This inductor serves to isolate the +5V
supply from the noise in the switching portion of the DC-DC
converter, and to limit the inrush current into the input capac-
itors during power up. A value of 2.5H is recommended.
It is necessary to have some low ESR aluminum electrolytic
capacitors at the input to the converter. These capacitors
deliver current when the high side MOSFET switches on.
Figure 7 shows 3 x 1000F, but the exact number required
will vary with the speed and type of the processor. For the
top speed Katmai and Coppermine, the capacitors should be
rated to take 9A and 6A RMS of ripple current respectively.
Capacitor ripple current rating is a function of temperature,
and so the manufacturer should be contacted to nd out the
ripple current rating at the expected operational temperature.
For details on the design of an input lter, refer to Applica-
tions Bulletin AB-15.
Figure 7. Input Filter
Active Droop
The RC5057 includes active droop: as the output current
increases, the output voltage drops. This is done in order to
allow maximum headroom for transient response of the con-
verter. The current is sensed by measuring the voltage across
the high-side MOSFET during its on time. Note that this makes
the droop dependent on the temperature of the MOSFET.
However, when the formula given for selecting RS (current
limit) is used, there is a maximum droop possible (-40mV),
and when this value is reached, additional drop across the
MOSFET will not cause any increase in droop—until current
limit is reached.
Additional droop can be added to the active droop using a
discrete resistor (typically a PCB trace) outside the control
loop, as shown in Figure 2. This is typically only required for
the most demanding applications, such as for the next gener-
ation Intel processor (tolerance = +40/-70mV), as shown in
Figure 2.
R5
SW
VOUT
1N4148
RSENSE
IFB
2.5
H
5V
0.1
F
1000
F, 10V
Electrolytic
Vin
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相关代理商/技术参数 |
参数描述 |
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| RC5057N | 功能描述:开关变换器、稳压器与控制器 DIP-16 RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| RC5058 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:High Performance Programmable Synchronous DC-DC Controller for Multi-Voltage Platforms |
| RC5058M | 功能描述:开关变换器、稳压器与控制器 SOIC-24 RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| RC5058MT | 功能描述:开关变换器、稳压器与控制器 SOIC-24 RoHS:否 制造商:Texas Instruments 输出电压:1.2 V to 10 V 输出电流:300 mA 输出功率: 输入电压:3 V to 17 V 开关频率:1 MHz 工作温度范围: 安装风格:SMD/SMT 封装 / 箱体:WSON-8 封装:Reel |
| RC5060 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:ACPI Switch Controller |
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