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Description of the Digital Phase-Shifted Full-Bridge Converter
12.4.3
Tasks Within IRQ and State Machine
Almost all firmware tasks occur during the IRQ. The exceptions are the serial interface and PMBus tasks,
which occur in the Background Loop; and the overcurrent protection (OCP), which is handled by the FIQ.
The IRQ is called to respond every 100 µs.
At the heart of the IRQ function is the power-supply State Machine implemented with switch command.
Figure 30
shows the structure of the State Machine. At a higher level, this State Machine allows the digital
controller to optimize the performance of the power supply based on the exact State Machine functions of
the digital controller.
12.4.4
Tasks Within Background Loop
The background loop handles all PMBus communication as well as processing and transmitting data
through the UART. The data flash is managed with a dual-bank approach. This provides redundancy in
the event of a power interruption during the programming of data flash. Once new data-flash values have
been written, a function called erase_task() initiates in the background loop to erase the old values. The
erase_task() is called until all of the old DFLASH segments are erased. Erasing the data flash in segments
allows the processor to handle other tasks instead of waiting for the entire data flash to be erased before
completing other tasks.
12.4.5
System Normal Operation
The EVM is designed to operate in peak-current-mode control under normal operation conditions. The
EVM operates with output voltage in regulation across the load range. If the load power continues to
increase beyond the rated value, then an overload condition occurs. In such a case, the system enters
protection operation by entering CPCC mode. If load power still continues to increase, output shutdown is
triggered.
34
Using the UCD3138PSFBEVM-027
Id le
P SO N a n d N o F a u lt s
R a m p u p
V o lt m o d e
R a m p u p O v er
S Y N F E T _
Pe a k C u r r e n t M o d e
R a m p _ u p
R am p U p D o n e
R a m p u p O v er
R e g u la te d
Figure 30. State Machine
Copyright © 2013, Texas Instruments Incorporated
PS O N O N
F a u lt s C le ar
F a u lt s
F A U L T
F a u lts
F a u lt s
www.ti.com
SLUUAK4 – August 2013
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