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AH478

SINGLE PHASE HALL EFFECT LATCH WITH LOCKED PROTECTION

BCD Semiconductor 

Data Sheet

SINGLE PHASE HALL EFFECT LATCH WITH LOCKED PROTECTION AH478

Operating Diagram (Note 3)

Hall Input

Motor Output

CT

ON

OFF

CT

Clamp

Voltage

CT

Comparator

Voltage

Motor locked

Motor lock detected

TON

TOFF

Motor lock

cleared

Reverts to normal operation

Note 3: The automatic restart circuit detects a motor lock condition and automatically turns off the output current. When the

lock is cleared, the IC automatically restarts and allows the motor to run. In AH478, automatic restart is performed in the fol-

lowing manner. A motor lock condition is detected when the Hall signal stops switching. The output is ON when CT pin is

being charged, and OFF when CT pin is being discharged.

TON = C * (VCL − VCP) (Sec)

ICHG

TOFF = C * (VCL − VCP ) (Sec )

IDHG

Output ON time (TON) and OFF time (TOFF) are determined by C, the capacitance of the CT pin external capacitor.

VCL is the CT pin clamp voltage

VCP is the CT pin comparator voltage

ICHG is the CT pin charge current

IDHG is the CT pin discharge current

Figure 12. Control Timing Diagram of AH478

Nov. 2008 Rev. 1. 2

BCD Semiconductor Manufacturing Limited

9

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