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RC5041M 参数 Datasheet PDF下载

RC5041M图片预览
型号: RC5041M
PDF下载: 下载PDF文件 查看货源
内容描述: 可编程的DC-DC转换器,用于奔腾P55C , K6和6x86MX ( M2)处理器 [Programmable DC-DC Converter for Pentium P55C, K6 and 6x86MX (M2) Processors]
分类和应用: 转换器DC-DC转换器
文件页数/大小: 16 页 / 121 K
品牌: RAYTHEON [ RAYTHEON COMPANY ]
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PRODUCT SPECIFICATION  
RC5041  
Main Control Loop  
Power Good  
Refer to the Block Diagram on page 1. The control loop of  
the regulator contains two main sections, the analog control  
block and the digital control block. The analog block con-  
sists of signal conditioning amplifiers feeding into a set of  
comparators which provide the inputs to the digital block.  
The signal conditioning section accepts inputs from the IFB  
(current feedback) and VFB (voltage feedback) pins and sets  
up two controlling signal paths. The voltage control path  
amplifies the VFB signal and presents the output to one of  
the summing amplifier inputs. The current control path takes  
the difference between the IFB and VFB pins and presents  
the resulting signal to another input of the summing ampli-  
fier. These two signals are then summed together with the  
slope compensation input from the oscillator. This output is  
then presented to a comparator, which provides the main  
PWM control signal to the digital control block.  
The RC5041 Power Good function is designed in accordance  
with the Pentium Pro DC-DC converter specification and  
provides a constant voltage monitor on the VFB pin. The  
circuit compares the VFB signal to the VREF voltage and  
outputs an active-low interrupt signal to the CPU should the  
power supply voltage exceed ±12% of its nominal setpoint.  
The Power Good flag provides no other control function to  
the RC5041.  
Over-Voltage Protection  
The RC5041 provides a constant monitor of the output  
voltage for protection against overvoltage conditions. If the  
voltage at the VFB pin exceeds 20% of the selected program  
voltage, an overvoltage condition will be assumed, and  
the RC5041 will disable the output drive signal to the  
MOSFET(s).  
The additional comparators in the analog control section set  
the thresholds of where the RC5041 enters its pulse skipping  
mode during light loads as well as the point at which the  
maximum current comparator disables the output drive sig-  
nals to the external power MOSFETs.  
Short Circuit Protection  
A current sense methodology is implemented to disable the  
output drive signal to the MOSFET(s) when an over-current  
condition is detected. The voltage drop created by the output  
current flowing across a sense resistor is presented to an  
internal comparator. When voltage developed across the  
sense resistor exceeds the comparator threshold voltage,  
the RC5041 will disable the output drive signal to the  
MOSFET(s).  
The digital control block is designed to take the comparator  
inputs along with the main clock signal from the oscillator  
and provide the appropriate pulses to the HIDRV output  
pin that controls the external power MOSFET. The digital  
section was designed utilizing high speed Schottky transistor  
logic, thus allowing the RC5041 to operate at clock speeds  
as high as 1MHz.  
The DC-DC converter returns to normal operation after the  
fault has been removed, for either an overvoltage or a short  
circuit condition.  
High Current Output Drivers  
Oscillator  
The RC5041 contains one high current output drivers which  
utilize high speed bipolar transistors arranged in a push-pull  
configuration. The driver is capable of delivering 1A of cur-  
rent in less than 100ns. The driver's power and ground are  
separated from the overall chip power and ground for addi-  
tional switching noise immunity.  
The RC5041 oscillator section is implemented using a  
fixed current capacitor charging configuration. An external  
capacitor (CEXT) is used to preset the oscillator frequency  
between 80KHz and 1MHz. This scheme allows maximum  
flexibility in setting the switching frequency as well as  
choosing external components.  
Internal Voltage Reference  
In general, a lower operating frequency will increase the  
peak ripple current flowing in the output inductor, and thus  
require the use of a larger inductor value. Operation at lower  
frequencies also increases the amount of energy storage that  
must be provided by the bulk output capacitors during load  
transients due to the slower loop response of the controller.  
The reference included in the RC5041 is a 1.24V precision  
band-gap voltage reference. The internal resistors are pre-  
cisely trimmed to provide a near zero temperature coefficient  
(TC). Added to the reference input is the resulting output  
from an integrated 4-bit DAC. The DAC is provided in  
accordance with the Pentium Pro specification guideline,  
which requires the DC-DC converter output to be directly  
programmable via a 4-bit voltage identification (VID) code.  
This code will scale the reference voltage from 2.0V (no  
CPU) to 3.5V in 100mV increments. For guaranteed stable  
operation under all loading conditions, a 10Kpull-up  
resistor and 0.1µF of decoupling capacitance should be  
connected to the VREF pin.  
The user should note that the efficiency losses due to switch-  
ing are relatively fixed per switching cycle. Therefore, as the  
switching frequency is increased, so is the contribution  
toward efficiency due to switching losses.  
Careful analysis of the RC5041 DC-DC controller has  
resulted in an optimal operating frequency of 300KHz,  
which allows the use of smaller inductive and capacitive  
components while maximizing peak efficiency under all  
operating conditions.  
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