ICE5QSAG データシートの表示（PDF） - Infineon Technologies

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ICE5QSAG

Quasi-Resonant Controller

Infineon Technologies 

Quasi-Resonant Controller

Functional Description

soft start, the ringing suppression time is set to 25 µs to avoid irregular switching due to switch off oscillation

noise.

Vcs (V)

VCS_Peak

0.75

0.60

0.45

0.30

ton

3

6

9

12 Time(ms)

Figure 5

Maximum current sense voltage during soft start

3.3

Normal Operation

During normal operation, the ICE5QSAG works with a digital signal processing circuit composing an up/down

counter, a zero-crossing counter (ZC counter) and a comparator, and an analog circuit composing a current

measurement unit and a comparator. The switch-on and -off time points are each determined by the digital

circuit and the analog circuit, respectively. The input information of the zero-crossing signal and the value of

the up/down counter are needed to determine the switch-on while the feedback signal VFB and the current

sensing signal VCS are necessary for the switch-off determination.

Details about the full operation of the controller in normal operation are illustrated in the following

paragraphs.

3.3.1

Digital Frequency Reduction

As mentioned above, the digital signal processing circuit consists of an up/down counter, a ZC counter and a

comparator. These three parts are the key to implement digital frequency reduction with decreasing load. In

addition, a ringing suppression time controller is implemented to avoid mis-triggering by the high frequency

oscillation, when the output voltage is very low under conditions such as soft start period or output short

circuit. Functionality of these parts is described as in the following.

3.3.1.1 Minimum ZC Count Determination

To reduce the switching frequency difference between low and high line, minimum ZC count determination is

implemented. Minimum ZC count is set to 1 if VIN less than VVIN_REF which represents for low line. For high line,

minimum ZC count is set to 3 after VIN higher than VVIN_REF. There is also a hysteresis VVIN_REF with certain blanking

time tVIN_REF for stable AC line selection between low and high line.

3.3.1.2 Up/down counter

The up/down counter stores the number of the zero crossing which determines valley numbers to switch-on

the main MOSFET after demagnetization of the transformer. This value is fixed according to the feedback

voltage, VFB, which contains information about the output power. Indeed, in a typical peak current mode

control, a high output power results in a high feedback voltage, and a low output power leads to a low

feedback voltage. Hence, according to VFB, the value in the up/down counter is changed to vary the power

Datasheet

7 of 27

V 2.1

2020-02-03

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