VTT er volt til termineringsresistorerne på ram-kredsen.
<i>DDR memory systems require both Vddq and Vtt voltage rails. While a standard supply type may be used for the Vddq output, a different type of power supply is required for the bus termination Vtt voltage. For these DDR bus termination supplies, the Vtt voltage generation circuit must be able to accurately track a reference voltage, Vref, which is 50 percent of the output supply voltage, Vddq. While Vddq may vary by ±200mV from its nominal value of 2.5V, Vtt must remain within ±40mV of Vref under all load and transient conditions. The circuit generating Vtt must also be able to sink current when the output buffer (line driver) is at a logic-high state and source current when the output buffer state is low. With the current-sinking mode, the current through the output inductor is reversed from the normal direction in a buck configuration. </i>