Datasheet

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
UCD3138
SLUSAP2F –MARCH 2012 –REVISED NOVEMBER 2013 www.ti.com
4.12.3 Mechanism for Automatic Mode Switching
The UCD3138 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.
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.
44 Functional Overview Copyright © 2012–2013, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Links: UCD3138