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A3987-Slide6

The current control section sets a constant current by looking at the voltage generated through the motor winding current going through the externally supplied sense resistor, R sense. The current control section then compares it to a voltage derived from an externally applied reference voltage, VREF and D to A inputs from the logic section. When VR sense equals the derived voltage from the logic section, the proper output transistor is turned off for a fixed “off-time” set by an external resistor from the logic voltage supply to R oscillator input. During the fixed off time, the current in the motor winding decays until the transistor is turned back on and the cycle starts all over again.

PTM Published on: 2011-10-13