LB1660 Sanyo, LB1660 Datasheet - Page 7

• Manufacturer Part Number: LB1660
• Description: 2-Phase Unipolar Brushless Motor Drivers
• Manufacturer: Sanyo

(4) Lock detect threshold voltage
CR Pin Peripheral Circuit
[Setting Method of Lock Detect Time]
(1) Generation of discharge pulse
Output transistor drive
The LB1660 series have the function to stop the output drive after the lapse of a given period of time when a motor is
locked, and period of time can be set by C, R3.
The CR pin peripheral equivalent circuit is shown below. The LB1660 series generate the CR pin discharge pulse when the
phase changes, (detection of rotation). When a motor is locked (very low rotational speed), the C connected to the CR pin
stops discharging and the CR pin voltage rises. When the CR pin voltage exceeds the threshold voltage (V
output drive current becomes zero and the output transistor is turned off, and the RD pin output turns from ‘‘L’’ to ‘‘H’’. The
RD pin output is of the open collector type.
Electric charges on C charged through R3 are discharged via route of C
change. When a fan has a high rotational speed, a lot of discharge pulses are generated and the CR pin voltage (=V
By contrast, when a fan has a low rotational speed, V
The discharge pulses are generated by two methods as shown below.
1
2
Discharge pulse
Generated internally at the time of phase change. The power transistor base storage time is used for discharge pulses.
When the kickback voltage induced by L of a motor coil is absorbed by the zener diode across collector and base of the
output transistor, this interval of time during which the transistor is turned on is used for discharge pulses.
Therefore, the LB1661,1665 or LB1660N, 1664N use external zener diodes and capacitors, discharge occurs with pulses
of 1 only and V
is the same.
CR pin voltage
t = 15 to 30 µsec
0.8 c V
RD pin
IN
CR
voltage gets higher than the circuit generating discharge pulses of 2 even if the CR time constant
LB1660N, 1661, 1664N, 1665
Motor lock
CR
rises and the protector is operated.
r
Output off
TRr with constant width pulses at each phase
IN
0.8), the
No.2551-7/9
CR
) drops.