AM4964 datasheet(11/21 Pages) DIODES

11 / 21 page

AM4964

Document number: DS37241 Rev. 2 - 2

11 of 21

www.diodes.com

June 2014

AM4964

A Product Line of

Diodes Incorporated

Functional Descriptions (cont.)

– Locked Rotor Timing Capacitor

The CT pin will have a capacitor connected to ground. It is a multi-function pin providing timing for the lock detect and auto-restart. Different

rates of charge and discharge of CT capacitor depending on the mode of operation (fan operation status) give the lock-detect time (tLCKDET) and

lock time (tOFF) before the next auto-start retry. When the motor is running, the capacitor is discharged at every Hall signal change.

CT pin provides the timing for the Locked Rotor monitor. In normal operation, Lock Detect is enabled. If the Hall signal does not change (i.e. a

rotor lock condition) within the Lock Detect time (tLCKDET), the outputs are disabled. In this condition the motor will not be driven for a set time tOFF.

This tOFF time depends on the external CT capacitor value and its internal discharge current (IDHG). After the tOFF period device enters auto-restart

phase to re-start the motor with a new Lock Detect time. If the motor has not turned to generate a transition on the Hall inputs by the end of this

tLCKDET period, the motor re-enters motor lock tOFF period with the outputs disabled. If the Hall signal change is detected, the motor is deemed as

running and goes into lock-detection mode. The tLCKDET and tOFF are determined by the value of the external capacitor on the CT pin and the

internal charge and discharge currents during these time periods. The currents during tLCKDET and tOFF are ICHG, and IDHG respectively.

– Frequency Generator (Tachometer) Output Pin

This is the Frequency Generator output and is a buffered signal from the Hall sensor. This is an open collector drive giving an active pull down

with the high level being provided by an external pull up resistor.

OUT1 and OUT2 Pins

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

VCC

– IC Supply voltage

This pin provides the supply for the device.

GND

– Supply Return

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

PGND

–Power Supply Return

This is the device supply ground return pin for power output pins OUT1 and OUT2 and will generally be the most negative supply pin to the fan.

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