Overview of Operation

Temperature Dependent Dynamic Voltage Scaling Implementation (XAPP1394)

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The default mode when the -2LI device is powered on is Voltage High mode (0.725 V) and the default VRM voltage for VCCINT should be set as this value. After the drivers are loaded and operating, the internal SYSMON of the AMD device continuously samples the junction temperature at 100 ms intervals. During this time, if the junction temperature (TJ) falls below or rises above the pre-determined thresholds, it triggers a voltage change.

This is executed by communication with the voltage regulator via I2C/PMBus to change to the appropriate voltage. The CDO file is configured to determine the I2C/PMBus operation, values, and configuration of the regulator.

Using these drivers, the AMD device operates as the PMBus/I2C master, and no other masters should be on the communication line because this might lead to contention and incorrect operation of the drivers. If there is already a master I2C/PMBus in your system, a configurable I/O can be used to indicate if the device should be in voltage high (0.725 V) or voltage low (0.7 V) mode by pulling the I/O to a High or Low state.

The thresholds for AMD DVS are seen in the following graph. There is an added window of hysteresis to prevent sudden changes to the voltage. It is important to note that other settings within your voltage regulator might need to change with the voltage. Overvoltage protection is one such example that needs to track with the output voltage. There are many regulators that can track over/undervoltage as a percentage of the output voltage to prevent additional register changes to the regulator during runtime. A regulator with a suitable ramp time between voltage Low/High must be used, and the voltage change must happen within 40 ms of the voltage indication.

Figure 1. Temperature Threshold and Voltage Change
Figure 2. System Implementation Diagram