UCD3138A datasheet(39/83 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

UCD3138A

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SLUSC66B – MARCH 2015 – REVISED MAY 2015

6.7.3

Mechanism for Automatic Mode Switching

The UCD3138A 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 in Figure 6-9.

Figure 6-9. 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.

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