As mentioned on the previous slide, the first drawback to voltage mode drive is back EMF. This slide illustrates the effects of back EMF and the results of the back EMF compensation. If the magnitude of the applied sine wave voltage remained constant over the operating speed, as shown here, the resulting current will decrease with speed as the back EMF increases and reduces the effective voltage across the coil. If the applied voltage is increased by an amount equal to the back EMF, the resulting current will remain the same over the operating speed, as shown on the right. The L6470 uses a set of registers that define the slope of the increase to be applied to the sine wave. Essentially the device multiplies the register value (slope) by current speed and adds that value to the programmed current magnitude. Different slopes can be defined for various portions of the operating profile.