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