TA8420 데이터 시트보기 (PDF) - Toshiba
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TA8420 Datasheet PDF : 12 Pages
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TA8420,21AF
OPERATION OF AUTOMATIC SELF RECOVERY CIRCUIT
If Motor Rotation is distorted by external force or obstacles, Over Current, which have a possibility of Drive Coil
Burning, is generated by decreasing of Back Electron Motive Force (BEMF).
Therefore, Over Heat Protection of Drive Coil is required for Fan Motor Drive System.
Generally, Series Connection of Temperature Dependence Elements (Posistor) to Output Drive Coil or to use drive
IC incorporates protection circuit are required to get coil burning protection.
Posistor is so expensive, therefore, IC’s incorporate this function are coming into wider use for Fan Motor Drive in
recent years.
Generally, re−switch operation after the turn on of protection circuit is required for system start up again because
the circuit is constructed by flip−flop circuits.
But there’s no use re−switch operation with TA8420AF, TA8421AF because of build−in automatic self recovery
circuit.
Fig.1 shows pin (10) voltage and the operation of this functions are as follows.
1. Normal rotation states
Internally generated charging current of ISL (0.25 µA Typ.) charge−ups external capacitance of CSC
connected to pin (10).
But FG pulse, generates among in rotation states and the frequency is proportional to rotation speed,
discharges CL charge periodically.
Therefore, voltage of pin (10) is becoming sawteeth waveform and will not to reach VSC of limiting voltage
(1.3 V Typ.).
2. Motor lock states
If a Motor is locked by external force or obstacles, internal FG pulse generation is stopped. As a result, the
voltage of pin (10) increase.
Torque generation is stopped after when the voltage of pin (10) reaches to VSC Further more, voltage of pin
(10) is increased by charging current of ISL toward the VSCR of self recovery voltage (2.9 V Typ.).
And then the pin (10) voltage reaches to VSCR.
Automatic self recovery circuit operates and generates a momentary torque (ton = 200 ms. Typ.). But Motor
can not start own rotation if the Motor is still locked by external force or obstacles.
In this period, voltage wave form of pin (10) is becoming sawteeth that peak is VSCR and Bottom is
Minimum DC level of approximately 0.7 V.
3. After release of motor lock
Pin (10) voltage can not reaches VSC level after release of Motor lock because of discharging operation of
CSC.
3
2001-06-13
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