Reaction Module Off Time Definition

This MotoHawk™ block allows the Hold Off Timers that reside within the Reaction Module to be set. Certain modulation schemes like Peak/Hold With Off Time (PHWOT) rely upon these timers to control aspects of the modulation. The timers are resource driven so that they can be assigned in the most efficient manner. Multiple reaction channel definitions may reference a timer definition.

Block ID

React Off Time

Library

MotoHawk_lib/ModuleConfiguration

Description

Signals

Off Time (ns)

Off Time is directly related to the Reaction Module's Hold Off Timers that are described in Freescale Semiconductor's REACM documentation. A Hold Off Timer is used to control the time that a channel is to remain off (once switched off by the silicon because the load current has exceeded the specified threshold) before it will turn back on again. This attribute partly defines the switching frequency a reaction channel behavior like Peak/Hold With Off Time (PHWOT) will exhibit by defining the off portion. The current threshold that specifies the turn off threshold is defined as part of the controlling behavior. Thus a PHWOT behavior defines a peak current threshold and a hold current threshold. A reaction channel will enter Hold Off and remain off for the Off Time before switching back on again.

This attribute provides the application with the mechanism to control the amount of current ripple that will be exhibited by the load. Larger Off Time values will tend to lead to larger ripple currents because the load current will be allowed to decay for longer before the driver is switched back on again. Lower values will lead to smaller ripple currents, but really low values can lead to runaway because the load current is sampled in software and thus is only approximately controlled against the current threshold. Consequently it is possible that the load current has not fallen sufficiently before being switched back on again when a small Off Time is used. This can lead to a load current that trends upward rather than holding at the specified threshold. The figure below illustrates.

Block Parameters

Parameter Field	Values	Comments/Description
Name	Alpha-numeric text, single-quote enclosed	This name will be used by associated blocks like the Peak/Hold Controller block to reference this timer definition. No special characters, such as spaces, dashes and commas (underscore allowed)
Resource	Drop-down list	Select internal resource for this block (target module dependent).