AM4964 datasheet(16/21 Pages) DIODES

16 / 21 page

AM4964

Document number: DS37241 Rev. 2 - 2

16 of 21

www.diodes.com

June 2014

AM4964

A Product Line of

Diodes Incorporated

Applications Note (cont.)

Adjustable Voltage

fPWM=25kHz

Low Speed

PWM Variable

High Speed

VMIN

VH=3.6V

VL=2.0V

All Parameters Are Tested under VCC=12V

VCF (T≤TL)

VCF (T≥TH)

FG Output(T

≤T

FG Output(T

≥T

Speed Control and Minimum Speed Setting

Minimum Speed Setting

The minimum speed setting prevents the motor speed dropping below a setting speed when the speed demand is too low (i.e. PWM voltage is

closer to 3.6V)

When the CF pin voltage is higher than the VMIN voltage, the VMIN voltage is compared with the internal triangular wave to generate the output

PWM duty. Therefore, setting the VMIN to certain fixed voltage forces the VMIN to control the speed even when the CF voltage is higher.

If VMIN setting is not used or application does not need to set the minimum speed, connect the VMIN to CF directly.

Rotor Lock Detect and OFF Tme Setting

The capacitor C4 from CT pin to the ground provides the timing for the lock detect and auto-restart. The capacitor C4 is charges and discharged by

the CT pin at a fixed rate depending on the mode of operation (fan operation status) and therefore the value of the C4 to gives lock-detect time

(TLCKDET) and lock time (TOFF) before next auto-start retry.

The AM4964 returns the C4 voltage to the low threshold, VCTL (1.77V), each time the Hall sensor provides the commutation signal. C4 is charged

with ICHG which is typically 2μA. If the voltage on the C4 reaches the high threshold, VCTH (3.7V) before the next Hall signal change, the output will

be shut down and the device will enter lock condition.

C DET

CTH

CHG

The thresholds voltage and charge current are fixed, therefore the tLCKDET time depends only on the value of C4.

C DET

For C4 of 0.47

μF, t

LCKDET is 0.47s.

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