Power

AL

A few hundred milliseconds

Hall Input

Motor Output

LD

AL

Motor

locked

On

Off

Clamp voltage

Comparator voltage

Motor lock

cleared

Motor lock

detected

t

ON

t

OFF

Return to

normal operation

TMP821

www.ti.com

SLDS152A – JANUARY 2008 – REVISED MAY 2015

7.3 Feature Description

7.3.1 Lock Detection

The TMP821 device comes with the built-in lock detect feature. If it's not able to rotate the rotor for a specific

amount of time, the Lock Detection disables the drive and retries after some time. The timings are dependant on

the capacitor connected at LD Pin.

When a motor lock is detected, the TMP821 device automatically shuts down its output current. When the motor

lock is removed, the TMP821 device automatically restarts. Motor lock is detected when the Hall signal stops

switching, as shown in Figure 3.

Figure 3. Motor Lock Diagram

tON and tOFF are determined by the capacitor connected to LD:

tON = (CLD × (VLD_CLAMP – VLD_COMP) / ILD_CHARGE (seconds)

(1)

tOFF = (CLD × (VLD_CLAMP – VLD_COMP) / ILD_DISCHARGE (seconds)

where

•

CLD = capacitance of the external capacitor on LD

•

VLD_CLAMP = LD clamp voltage

•

VLD_COMP = LD comparator voltage

•

ILD_CHARGE = LD charge current

•

ILD_DISCHARGE = LD discharge current

(2)

Figure 4. Power-on to AL Delay

7.3.2 Speed Sensing

The TMP821 device gives the speed information on the pin AL. This pin may remain high for few hundred

milliseconds at the start-up. Once the motor attains some speed, the frequency can be observed at this pin.

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