Forced Quasi Resonant ZVS flyback controller
Functional Description
4
Functional Description
The functional description gives an overview about the integrated functions and features and their relationship. The
mentioned parameters and equations are based on typical values at TA = 25 °C. The correlated minimal and maximal values
are shown in the electrical characteristics in Chapter 6.
The functional description is grouped in following sections:
Power supply management (Chapter 4.1)
Control features (Chapter 4.2)
Protection features (Chapter 4.3)
4.1
Power supply management
The power supply management ensures a reliable and robust IC operation. Depending on the operation mode of the control
IC, the power supply management unit runs in different ways for VCC supply and for brown-in monitoring, which are
described in the sequel:
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VCC capacitor charge-up and startup sequence (see Chapter 4.1.1)
Brown-in monitoring (Chapter 4.1.2)
Brown-out protection response (Chapter 4.1.3)
During burst mode (QBM) operation (Chapter 4.1.4)
Bang-bang mode during latch mode (LM) operation (Chapter 4.1.5.1 )
Bang-bang mode during auto-restart mode (ARM) operation (Chapter 4.1.5.2)
4.1.1
VCC capacitor charge-up and startup sequence
There are two main functions supported at HV pin by a resistor RHV connected to the bulk capacitor (see Figure 5). They are
the VCC capacitor charge-up, and the bulk voltage monitoring (see Chapter 4.1.2).
At beginning of a cold startup, the depletion startup cell is on. Once the AC line voltage is applied and charging the bulk
capacitor, a current flows through the external resistor RHV into HV pin. Via the integrated diode D1, that current may charge
up the external VCC capacitor (see Figure 5). Once VCC voltage exceeds the threshold VVCCon = 20.5 V, the startup cell is turned
off, the control IC is enabled and the firmware boot sequence follows which takes about 1.2 ms. Both bulk voltage brown-in
and VCC brown-in condition (see Chapter 4.3.4) are checked continuously. Once they both are above the brown-in level,
respectively, the first GD0 pulse according to the soft-start control will be generated earliest after the 1.2 ms boot sequence
time. The voltage VVCC drops until the supply via the auxiliary winding (VVCCSS) takes over the VCC supply (see Figure 4). For a
proper system startup and operation, the supply voltage VVCC must be always above the VCC off-threshold VVCCoff=7.2 V (see
Chapter 4.3.3).
Data Sheet
7
Revision 2.0
2020-08-20
INFINEON [ Infineon ]
