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CM6800GIP 参数 Datasheet PDF下载

CM6800GIP图片预览
型号: CM6800GIP
PDF下载: 下载PDF文件 查看货源
内容描述: 低启动电流PFC / PWM控制器, COMBO [LOW START-UP CURRENT PFC/PWM CONTROLLER COMBO]
分类和应用: 功率因数校正控制器
文件页数/大小: 18 页 / 289 K
品牌: CHAMP [ CHAMPION MICROELECTRONIC CORP. ]
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CM6800  
LOW START-UP CURRENT PFC/PWM CONTROLLER COMBO  
The output of the gain modulator is a current signal, in the  
In higher power applications, two current transformers are  
sometimes used, one to monitor the IF of the boost diode. As  
stated above, the inverting input of the current error amplifier  
is a virtual ground. Given this fact, and the arrangement of  
the duty cycle modulator polarities internal to the PFC, an  
increase in positive current from the gain modulator will  
cause the output stage to increase its duty cycle until the  
voltage on ISENSE is adequately negative to cancel this  
increased current. Similarly, if the gain modulator’s output  
decreases, the output duty cycle will decrease, to achieve a  
less negative voltage on the ISENSE pin.  
form of a full wave rectified sinusoid at twice the line  
frequency. This current is applied to the virtual-ground  
(negative) input of the current error amplifier. In this way the  
gain modulator forms the reference for the current error  
loop, and ultimately controls the instantaneous current draw  
of the PFC form the power line. The general for of the  
output of the gain modulator is:  
I
AC× VEAO  
x 1V  
IGAINMOD  
=
(1)  
2
V
RMS  
Cycle-By-Cycle Current Limiter and Selecting RS  
More exactly, the output current of the gain modulator is  
given by:  
The ISENSE pin, as well as being a part of the current feedback  
loop, is a direct input to the cycle-by-cycle current limiter for  
the PFC section. Should the input voltage at this pin ever be  
more negative than –1V, the output of the PFC will be  
disabled until the protection flip-flop is reset by the clock  
pulse at the start of the next PFC power cycle.  
IGAINMOD = K x (VEAO – 0.625V) x IAC  
Where K is in units of V-1  
Note that the output current of the gain modulator is limited  
around 228.47 μA and the maximum output voltage of the  
gain modulator is limited to 228.47uA x 3.5K=0.8V. This  
0.8V also will determine the maximum input power.  
RS is the sensing resistor of the PFC boost converter. During  
the steady state, line input current x RS = IGAINMOD x 3.5K.  
Since the maximum output voltage of the gain modulator is  
IGAINMOD max x 3.5K= 0.8V during the steady state, RS x line  
input current will be limited below 0.8V as well. Therefore, to  
choose RS, we use the following equation:  
However, IGAINMOD cannot be measured directly from ISENSE  
.
ISENSE = IGAINMOD-IOFFSET and IOFFSET can only be measured  
when VEAO is less than 0.5V and IGAINMOD is 0A. Typical  
IOFFSET is around 60uA.  
RS =0.8V x Vinpeak/(2x Line Input power)  
For example, if the minimum input voltage is 80VAC, and the  
maximum input rms power is 200Watt, RS = (0.8V x 80V x  
1.414)/(2 x 200) = 0.226 ohm.  
Selecting RAC for IAC pin  
IAC pin is the input of the gain modulator. IAC also is a  
current mirror input and it requires current input. By  
selecting a proper resistor RAC, it will provide a good sine  
wave current derived from the line voltage and it also helps  
program the maximum input power and minimum input line  
voltage.  
PFC OVP  
In the CM6800, PFC OVP comparator serves to protect the  
power circuit from being subjected to excessive voltages if  
the load should suddenly change. A resistor divider from the  
high voltage DC output of the PFC is fed to VFB. When the  
voltage on VFB exceeds 2.75V, the PFC output driver is shut  
down. The PWM section will continue to operate. The OVP  
comparator has 250mV of hysteresis, and the PFC will not  
restart until the voltage at VFB drops below 2.50V. The VFB  
power components and the CM6800 are within their safe  
operating voltages, but not so low as to interfere with the  
boost voltage regulation loop. Also, VCC OVP can be served  
as a redundant PFCOVP protection. VCC OVP threshold is  
17.9V with 1.5V hysteresis.  
RAC=Vin peak x 7.9K. For example, if the minimum line  
voltage is 80VAC, the RAC=80 x 1.414 x 7.9K=894Kohm.  
Current Error Amplifier, IEAO  
The current error amplifier’s output controls the PFC duty  
cycle to keep the average current through the boost  
inductor a linear function of the line voltage. At the inverting  
input to the current error amplifier, the output current of the  
gain modulator is summed with a current which results from  
a negative voltage being impressed upon the ISENSE pin.  
The negative voltage on ISENSE represents the sum of all  
currents flowing in the PFC circuit, and is typically derived  
from a current sense resistor in series with the negative  
terminal of the input bridge rectifier.  
2008/10/23 Rev. 2.1  
Champion Microelectronic Corporation  
Page 9