LB11922_08 Datasheet, PDF (14/15 Pages) Sanyo Semicon Device – For OA Products Three-Phase Brushless Motor Driver

LB11922
8. Forward/Reverse Switching
The motor rotation direction can be switched using the F/R pin. However, the following notes must be observed if the
motor direction is switched while the motor is turning.
• This IC is designed to avoid through currents when switching directions. However, increases in the motor supply
voltage (due to instantaneous return of motor current to the power supply) during direction switching may cause
problems. The values of the capacitors inserted between power and ground must be increased if this increase is
excessive.
• If the motor current after direction switching exceeds the current limit value, the PWM drive side outputs will be
turned off, but the opposite side output will be in the short-circuit braking state, and a current determined by the motor
back EMF voltage and the coil resistance will flow. Applications must be designed so that this current does not exceed
the ratings of the output transistors used. (The higher the motor speed at which the direction is switched, the more
severe this problem becomes.)
9. Brake Switching
The LB11922 provides short-circuit braking implemented by turning the output transistors for the high side for all
phases (UH, VH, and WH) on. (The opposite side transistors are turned off for all phases.) Note that the current limiter
does not operate during braking. During braking, the duty is set to 100%, regardless of the motor speed. The current
that flows in the output transistors during braking is determined by the motor back EMF voltage and the coil resistance.
Applications must be designed so that this current does not exceed the ratings of the output transistors used. (The higher
the motor speed at which braking is applied, the more severe this problem becomes.)
The braking function can be applied and released with the IC in the start state. This means that motor startup and stop
control can be performed using the brake pin with the S/S pin held at the low level (the start state).
10. Constraint Protection Circuit
The LB1922M includes an on-chip constraint protection circuit to protect the IC and the motor in motor constraint
mode. If the LD output remains high (indicating the locked state) for a fixed period in the start state, the upper side
(external) transistors are turned off. This time is set by the capacitance of the capacitor attached to the CSD pin.
When VCC = 6.3V : The set time (in seconds) is 74 × C (μF)
When VCC = 5.0V : The set time (in seconds) is 60 × C (μF)
To clear the rotor constrained protection state, the application must either switch to the stop state for a fixed period
(about 1ms or longer) or turn off and reapply power.
If the rotor constrained protection circuit is not used, a 220kΩ resistor and a 1500pF capacitor must be connected in
parallel between the CSD pin and ground. Since the CSD pin also functions as the power-on reset pin, if the CSD pin
were connected directly to ground, the IC would go to the power-on reset state and motor drive operation would remain
off. The power-on reset state is cleared when the CSD pin voltage rises above a level of about 0.64V.
11. Low-Voltage Protection Circuit
The LB11922 includes a low-voltage protection circuit to protect against incorrect operation when power is first
applied or if the power-supply voltage (VCC) falls. The (external) upper side output transistors are turned off if VCC
falls under about 3.75V (tpyical), and this function is cleared at about 4.0V (typical).
12. Power Supply Stabilization
Since this IC is used in applications that draw large output currents, the power-supply line is subject to fluctuations.
Therefore, capacitors with capacitances adequate to stabilize the power-supply voltage must be connected between the
VCC pin and ground. If diodes are inserted in the power-supply line to prevent IC destruction due to reverse power
supply connection, since this makes the power-supply voltage even more subject to fluctuations, even larger capacitors
will be required.
13. Ground Lines
The signal system ground and the output system ground must be separated and a single ground point must be taken at
the connector. Since the output system ground carries large currents, this ground line must be made as short as possible.
Output system ground ... Ground for Rf and the output diodes
Signal system ground ... Ground for the IC and the IC external components
No.7497-14/15