FA5527 FUJI [Fuji Electric], FA5527 Datasheet - Page 32

• Manufacturer Part Number: FA5527
• Description: Fuji Switching Power Control IC
• Manufacturer: FUJI [Fuji Electric]

(Reference)
Sub-harmonic oscillation and slope
compensation
converter operates in an inductor-current continuous mode
and at duty cycle of 50% or more, the current may oscillate
at an integral multiple of switching frequency. This
oscillation is called subharmonic oscillation.
when a subharmonic oscillation occurs.
value of an inductor current, switching cycle and current
slopes during ON and OFF periods remain unchanged.
contained in the output voltage or cause an unusual noise.
for preventing a subharmonic oscillation is given by the
following relational expression:
Here,
Lu：Gradient of an inductor current during the ON period
Ld：Gradient of an inductor current during the OFF period
Kc：Gradient of slope compensation
The above parameters are shown in Fig.45.
AN-087E Rev.1.0
April-2011
Kc
a certain gradient to the threshold of the peak current as
shown in Fig. 44. This is called slope compensation.
In a peak-value-control current mode, when the
Fig. 43 shows an example of inductor current waveform
It is found that ON and OFF periods vary while the peak
The harmonic oscillation may increase ripple voltage
The subharmonic oscillation can be prevented by giving
Generally, the gradient of slope compensation required

Fuji Electric Co., Ltd.
Ld

2
Lu
FA5526/5527/5528/5536/5537/5538
Fig.43 Inductor current without slope compensation
Fig.45 Inductor current without slope compensation
Fig.44 Inductor current with slope compensation
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