Digital PFC Description
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12.4.1 Background Loop
The firmware starts from function main(). In this function, after the system initialization, it goes to an infinite
loop. All the non-time critical tasks are put in this loop, it includes:
• Calculate voltage feed forward.
• Clear current offset at zero load.
• System monitoring.
• PMBus communication.
• Primary and secondary UART communication.
NOTE: User can always add any non-time critical functions in this loop.
12.4.2 Voltage Loop Configuration
The voltage control loop is a pure firmware loop. V
OUT
is sensed by a 12-bit ADC, and compared with
voltage reference. The error goes into a firmware Proportional-Integral (PI) controller, and its output is
used to do current loop reference calculations.
12.4.3 Current Loop Configuration
Current loop consists of several modules:
• Front End (FE) Module, to configure the AFE block gain.
– For single phase PFC, AFE0 is used.
• Filter Module, to configure the current loop compensation.
– FILTER1 is used.
• DPWM Module, to generate the PWM signal driving PFC.
– For single phase PFC, DPWM1B is used.
NOTE: Loop Mux Module, to configure interconnection among front end, filter and DPWM modules.
12.4.4 Interrupts
There are two interrupts, the Standard Interrupt (IRQ), and the Fast Interrupt (FIQ).
• IRQ contains the state machine and most of the PFC control firmware.
• FIQ is used in relation to implementing OVP protections.
38
Digitally Controlled Single-Phase PFC Pre-Regulator SLUU885B–March 2012–Revised July 2012
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Copyright © 2012, Texas Instruments Incorporated
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