LB11920 Datasheet, PDF (9/10 Pages) Sanyo Semicon Device – Three-Phase Brushless Motor Driver for Office Equipment Applications

LB11920
Continued from preceding page.
4. Power save circuit
This IC enters the power save condition to decrease the current dissipation in the stop mode. In this condition, the
bias current of most of circuits is cut off.
5. Forward/backward changeover
The motor rotation can be changed over with the F/R pin. Following cautions should be observed when F/R
changeover is to be made while the motor is running:
• The circuit incorporates a measure against the through current at a time of changeover. However it is necessary to
take an appropriate measure to prevent the voltage from exceeding the rated voltage (35 V) because of rising of the
VM voltage at changeover (instantaneous return of the motor current to the power supply). When this is a problem,
increase the capacitance of a capacitor between VM and GND.
• When the motor current after changeover is the current limit or more, the lower Tr is turned OFF. But the upper Tr
enters the short-brake condition, and the current determined from the motor counter-electromotive voltage and coil
resistance flows. It is necessary to prevent this current from exceeding the rated current (3.5 A). (F/R changeover
at high rotation speed is dangerous.)
6. Brake operation
Brake operation is made through setting of the BR pin to the “L” level. This operation consists of a short-brake
operation in which all of lower outputs are turned OFF while all of upper outputs are turned ON. While the brake is
operating, current limiting and motor lock protection circuits are not operative. Apply brake only when the current
during operation does not exceed the rated current (3.5 A).
The circuit incorporates a measure against the through current at a time of changeover. However it is necessary to
take an appropriate measure to prevent the voltage from exceeding the rated voltage (35 V) because of rising of the
VM voltage at changeover (instantaneous return of the motor current to the power supply). When this is a problem,
increase the capacitance of a capacitor between VM and GND.
7. Motor lock protection circuit
A motor lock protection circuit is incorporated for protection of IC and motor when the motor is locked.
The lower output Tr is turned OFF when the Hall input signal is not switched for a certain period in the motor drive
condition.
The time is set by means of a capacity of a capacitor connected to the CSD pin.
Time setting of about 3.5 sec is possible for the capacitance of 10 µF. (Variance ±30%)
Set time (s) ≈ 0.35 × C (µF)
Due care must be taken on any leakage current in the capacitor used because it may adversely affect error of the set
time, etc.
To cancel the motor lock protection condition, one of following steps must be taken:
• Stop mode
• Maintaining the output duty 0% condition through input of PWMIN or TOC for more than the period of tPWM × 8.
(tPWM: IC internal PWM oscillation period)
• Power must be applied again (in the stop condition).
Connect the CSD pin to GND when the motor lock protection circuit is not to be used.
The motor lock protection active period at restart becomes shorter than the setting when the stop time to cancel motor
lock protection is shorter because the charge of capacitor cannot be fully discharged. Therefore, it is necessary to
provide a certain allowance to the stop period while referring to the following formula as a guideline.
Stop time(ms) ≥ 15 × C (µF)
8. Circuit for low-voltage protection
This circuit detects the voltage applied to the V_CC pin. When this voltage drops below the operation voltage (see the
electric characteristics), the lower side output is turned OFF. To prevent repetition of output ON/OFF near the
protection activation voltage, the hysteresis is provided. Accordingly, the output is not recovered unless the voltage
rises by about 0.5 V above the activation voltage.
9. HP output
For the HP output, the composite signal of three phases of Hall element signal is output. This is an open collector
output. This can be used for the motor rotation detection signal, etc.
Continued on next page.
No. 7229-9/10