AM9469

Document number: DS38810 Rev. 2 - 2

9 of 16

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April 2018

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AM9469

Application Notes

H-Bias

– Hall Bias Output

This is a 1.25V nominal voltage source to bias a differential un-buffered Hall element sensor. If a Hall element requires a lower voltage than the

H-Bias output, connect an appropriate value resistor between the H-Bias Pin and the Hall element supply pin.

IN1 and IN2

– Hall Inputs

The rotor position is detected by a Hall sensor, with the output of Hall sensor applied to the IN1 and IN2 Pins. This sensor can be either a 4-pin

―naked‖ Hall device or of the 3-pin buffered switching type. For a 4-pin device the differential Hall output signal is connected to the IN1 and IN2

Pins. For a buffered Hall sensor, the Hall device output is attached to the IN1 Pin, with a pull-up attached if needed. Meanwhile, the IN2 pin has

an external potential divider attached to hold the pin at half VREF. When IN1 is high in relation to IN2, OUT2 is the active drive.

PWM Pin

– External PWM Signal Input for PWM Speed Control Mode

In PWM speed control mode, external PWM signal is applied at this PWM Pin to control the motors speed. The duty ratio of the PWM signal input

to this pin controls the fan motor speed by varying the output PWM drive directly.

CPWM Pin

Internal motor control triangular wave is generated based on the capacitor on this pin. A capacitor of 100pF (CPWM = 100pF), will provide a

triangular wave of 36kHz (typ). The VCONT and RMI signals are compared with this triangular wave to generate the speed control PWM drive and

minimum speed control clamp points. The output PWM drive frequency is the same as the triangular waveform frequency.

FG/RD Pin

FG is the Frequency Generator (tachometer) output and is a buffered signal from the Hall sensor. RD is the fan locked status detector. FG and

RD are open-drain outputs and will require external pull-up resistors. Typically, a pull-up resistor of 10k

Ω is recommended from the FG and RD

Pins to the supply voltage.

RF Pin

The current limiter is activated when the voltage between current detection resistor exceeds 0.25V between GND and RF. The current limiter is

activated at IO = 250mA when RF = 1Ω. The current limit is set with a RF resistor between the RF Pin and GND Pin.

RMI Pin

– Minimum Speed Setting Pin

RMI is the minimum speed setting pin. DC voltage on this pin sets the minimum speed value. If you do not use RMI (minimum speed control),

please connect it to 5VREG.

VCONT Pin

– DC Voltage Speed Control

VCONT is DC voltage inputs speed control pin. The voltage on the VCONT Pin is compared with the triangular oscillation on the CPWM Pin to

generate the output drive PWM signal. For the control method, refer to the timing chart.

REGH/5VREG Pin

Please insert capacitor value 1µF between 5VREG and GND for regulated output voltage stabilization; insert capacitor value 1µF value between

VDD and REGH for stable output voltage.

OUT1 and OUT2 Pins

OUT1 and OUT2 Pins provide H-bridge driver output for fan and motor coil connection.

VDD – Device Supply Voltage

This provides the supply for the device.

GND

– Supply Return

This is the device supply ground return pin for control signal.