Fan motor drivers with built-in hall element

Fan motor drivers with built-in hall element

*ROHM November survey

Overview | Highlight 1 | Highlight 2 | Highlight 3 | Lineup | Applications

Overview

ROHM offers the BU6909AGFT fan motor drivers with built-in Hall element ideal for cooling fans in notebook PCs, tablets, gaming consoles, and more. Additional features include a compact package, Auto Gain Control function, PWM soft switching for silent operation, and a standby function that minimizes battery consumption.   TSSOF6

Highlight 1: Hall element built in for greater space savings

The integrated Hall element not only cuts the number of external components, it reduces the entire IC to the size and thickness of a typical Hall element IC for significant space reduction.   Hall element built in for greater space savings

Highlight 2: PWM soft switching drive

This function gradually changes the PWM duty based on the Hall signal before and after output phase switching for smooth output current control. An AGC function is built in - an industry first. In addition, Hall signal linear detection, combined with PWM soft switching drive, minimizes Hall signal waveform variations, resulting in improved rotational efficiency and noise characteristics.

Highlight 3: AGC function improves noise characteristics via gain correction

AGC is a type of auxiliary circuit that maintains a constant output, regardless of the input signal level. In the case of a weak input signal, sensitivity is increased, and, conversely, for stronger input signals the sensitivity is decreased. In this way, the input signal can be varied to maintain a constant output.
Hall signals are susceptible to environmental changes within the fan motor section, which can lead to amplitude variations. For example, the rotor within a fan motor rotates slightly up and down. Naturally, as the distance becomes closer the sensitivity rises and the Hall amplitude increases. In addition, there are differences in the strength of the magnetic field of the magnet, along with effects from the temperature characteristics of the Hall element. The AGC corrects for these factors, resulting in an optimal amplitude and significantly improved noise characteristics.
 
Case 1: Increased Hall Amplitude (Primary Root Causes: Rotor distance too close, magnetic field too strong)
Case 1: Increased Hall Amplitude (Primary Root Causes: Rotor distance too close, magnetic field too strong)
 
Case 2: Decreased Hall Amplitude (Primary Root Causes: Rotor distance too far, magnetic field too weak)
Case 2: Decreased Hall Amplitude (Primary Root Causes: Rotor distance too far, magnetic field too weak)

Lineup

Internal Hall Element
Part No. Supply Voltage[V] Io max
[mA]
Output Saturation Voltage[V] Speed Control AGC Function Package
(mm)
BU6909AGFT 1.8~5.5 800 Upper and Lower total 0.16
(Io=200mA)
PWM TSSOF6
(2.9×3.8×0.75)

Applications

Thin, compact fan motors such as cooling fans for notebook PCs

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