Overview
The LB11850VA is a single-phase bipolar fan motor driver with speed control function that works with a speed feedback signal. A highly efficient, quiet and low power consumption motor driver circuit, with a high speed accuracy and large variable speed can be implemented by adding a small number of external components. This pre-driver is optimal for driving large scale fan motors (with large air volume and large current) such as those used in servers and consumer products.

Functions and features
• Pre-driver for single-phase full-wave drive
    →PMOS-NMOS is used as an external power TR, enabling high-efficiency and low-power-consumption drive by means of the low-saturation output and single-phase full-wave drive.
• On-chip speed control circuit
    →The speed control (closed loop control) using a speed feedback signal makes it possible to achieve higher speed accuracy and lower speed fluctuations when supply voltage fluctuates or load fluctuates, compared with an open loop control system. Separately excited upper direct PWM control method is used as the variable-speed control system.
• External PWM input or analog voltage input enabling variable speed control
    →The speed control input signal is compatible with PWM duty ratio or analog voltages.
• On-chip soft start circuit
• Lowest speed setting pin
    →The lowest speed can be set with the external resistor.
• Current limiter circuit incorporated
    →Chopper type current limit at start or lock.
• Reactive current cut circuit incorporated
    →Reactive current before phase change is cut to enable silent and low-consumption drive.
• Constraint protection and automatic reset functions incorporated
• FG (speed detection), RD (lock detection) output
• Constant-voltage output pin for hall bias