Filter Duty
Low – Lower Threshold
High – Lower Threshold
Control
Register 1
Auto Config High
Auto Config Mid
High – Upper Threshold
Low – Upper Threshold
0
Full Range
Automatic Mode Switching
With Hysteresis
Automatic Mode Switching
49
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
Digital Pulse Width Modulator (DPWM)
Figure 2-12. Mechanism for Automatic Mode Switching in UCD3138
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 Control Register 1 until the Low Lower Threshold is passed. This prevents oscillation between
modes if the filter duty is close to a mode switching point. In some applications it is necessary to make the
values the same, disabling hysteresis. This has to be done to make the DPWM signals from the two
modes match properly at the mode switching point.