UCD3138128PFC datasheet(29/80 Pages) TI

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Filter Duty

Low – Lower Threshold

High – Lower Threshold

Control

Auto Config High

Auto Config Mid

High – Upper Threshold

Low – Upper Threshold

Full Range

Automatic Mode Switching

With Hysteresis

UCD3138128, UCD3138A64

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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.

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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