UCD3138128_15 Datasheet, PDF (29/80 Pages) Texas Instruments – UCD3138x Highly-Integrated Digital Controller For Isolated Power

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UCD3138128, UCD3138A64
SLUSBZ8A – JUNE 2014 – REVISED SEPTEMBER 2014
9.3.3.3 Mechanism For Automatic Mode Switching
The UCD3138x allows the customer to enable up to two distinct levels of automatic mode switching. These
different modes are used to enhance light load operation, short circuit operation and soft start. Many of the
configuration parameters for the DPWM are in DPWM Control Register 1. For automatic mode switching, some
of these parameters are duplicated in the Auto Config Mid and Auto Config High registers.
If automatic mode switching is enabled, the filter duty signal is used to select which of these three registers is
used. There are 4 registers which are used to select the points at which the mode switching takes place. They
are used as shown below.
Automatic Mode Switching
With Hysteresis
Filter Duty
High – Lower Threshold
Low – Lower Threshold
Auto Config High
Auto Config Mid
Control
Register 1
Full Range
High – Upper Threshold
Low – Upper Threshold
0
Figure 15. Automatic Mode Switching
As shown, the registers are used in pairs for hysteresis. The transition from Control Register 1 to Auto Config
Mid only takes place when the Filter Duty goes above the Low Upper threshold. It does not go back to Auto
Config Mid until the Low Lower Threshold is passed. This prevents oscillation between modes if the filter duty is
close to a mode switching point.
9.3.4 DPWMC, Edge Generation, Intramux
The UCD3138x has hardware for generating complex waveforms beyond the simple DPWMA and DPWMB
waveforms already discussed – DPWMC, the Edge Generation Module, and the IntraMux.
DPWMC is a signal inside the DPWM logic. It goes high at the Blanking A begin time, and low at the Blanking A
end time.
The Edge Gen module takes DPWMA and DPWMB from its own DPWM module, and the next one, and uses
them to generate edges for two outputs. For DPWM3, the DPWM0 is considered to be the next DPWM. Each
edge (rising and falling for DPWMA and DPWMB) has 8 options which can cause it.
The options are:
0 = DPWM(n) A Rising edge
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