AP3984

Document number: DS37655 Rev. 3 - 2

8 of 15

www.diodes.com

December 2016

© Diodes Incorporated

AP3984

Multiple Segment Peak Current

As to the original PFM PSR system, the switching frequency decreases with decreasing of output current, which will encounter audible noise

issue since switching frequency decreases to audio frequency range about less than 20kHz.

In order to avoid audible noise issue, AP3984 uses 3-segment primary peak current control method at constant voltage (CV) mode, the current

NL mode is different, which will be described in next section.

It can be seen from the following figure that with multiple segment peak current control, AP3984 power system can keep switching frequency

above 24kHz from light load to heavy load and guarantee the audible noise free performance.

100%

45%

7%

50/55/60KHz

22.5/24.7/27KHz

FM

AM

FM

Figure 5. Segment Peak Current and Operating Frequency at CV Mode

Amplitude Modulation (AM)

The power transferring from the input to the output is given by:

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In AP3984, the high load mode and light load mode adopt the frequency modulation (FM), and the medium load mode uses the amplitude

modulation (AM).

We can get the square root equation from the following equation:

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So,

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2

2