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參數(shù)資料
| 型號： | GM3843AS8R |
| 廠商： | American Power Management Inc. |
| 英文描述： | HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS |
| 中文描述： | 高性能電流模式PWM控制器 |
| 文件頁數(shù)： | 2/19頁 |
| 文件大小： | 304K |
| 代理商： | GM3843AS8R |
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Current mode converters can exhibit subharmonic oscillations when operating at a duty cycle greater than 50%
with continuous inductor current. This instability is independent of the regulators closed–loop characteristics and
is caused by the simultaneous operating conditions of fixed frequency and peak current detecting. Figure 9.A
shows the phenomenon graphically. At t0, switch conduction begins and causes causing the inductor current to
rise at a slope of m1. This slope is a function of the input voltage divided by the inductance. At t1, the Current
Sense Input
reaches the threshold established by the control voltage.
This causes the switch to turn off and the current to decay at a slope of m2 until the next oscillator cycle. The
unstable condition can be shown if a pertubation is added to the control voltage, and resulting in a small DI
(dashed line). With a fixed oscillator period, the current decay time is reduced and the minimum current at switch
turn–on (t2) is increased by DI + DI m2/m1. The minimum current at next cycle (t3) decreases to (DI + DI m2/m1)
(m2/m1). This pertubation is multiplied by m2.m1 on each succeeding cycle, alternately increasing and decreasing
the inductor current at switch turn–on. Several oscillator cycles may be required before the inductor current
reaches zero, which caused causing the process to commence again. If m2/m1 is greater than 1, the converter
will be unstable. Figure 9.B shows that by adding an artificial ramp, that is synchronized with the PWM clock to
the control voltage, the DI pertubation will decrease to zero on succeeding cycles. This compensation ramp (m3)
must have a slope equal to or slightly greater than m2/2 for stability. With m2/2 slope compensation, the average
inductor current follows the control voltage yielding true current mode operation. The compensating ramp can be
Control Voltage
DI
Inductor
Current
t0
t1
t2
t3
DI + DI
m2
m1
m2
m1
(DI + DI
) (
)
m2
m1
Oscillator Period
A
B
Control Voltage
DI
Oscillator Period
m1
m2
m3
Inductor
Current
t4
t5
t6
Figure 9. Continuous Current Waveforms
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| GM3843AS8T | 制造商:GAMMA 制造商全稱:GAMMA 功能描述:HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS |
| GM3844A | 制造商:GAMMA 制造商全稱:GAMMA 功能描述:HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS |
| GM3844AD8T | 制造商:GAMMA 制造商全稱:GAMMA 功能描述:CURRENT MODE PWM CONTROLLER |
| GM3844AS8R | 制造商:GAMMA 制造商全稱:GAMMA 功能描述:CURRENT MODE PWM CONTROLLER |
| GM3844AS8T | 制造商:GAMMA 制造商全稱:GAMMA 功能描述:CURRENT MODE PWM CONTROLLER |
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