LB11870_07 SANYO [Sanyo Semicon Device], LB11870_07 Datasheet - Page 11

• Manufacturer Part Number: LB11870_07
• Description: For Polygonal Mirror Motors Three-Phase Brushless Motor Driver
• Manufacturer: SANYO [Sanyo Semicon Device]

Continued from preceding page.
Overview of the LB11870
1. Speed Control Circuit
2. Output Drive Circuit
3. Current Limiter Circuit
Pin No.
2, 4, 5
20, 30
31, 41
42, 43
45, 47
7, 18
This IC adopts a PLL speed control technique and provides stable motor operation with high precision and low jitter.
This PLL circuit compares the phase error at the edges of the CLK signal (falling edges) and FG signal (falling edges
on the FGIN+ and FGS signals), and the IC uses the detected error to control motor speed.
During this control operation, the FG servo frequency will be the same as the CLK frequency.
To minimize power loss in the output circuits, this IC adopts a direct PWM drive technique. The output transistors
are always saturated when on, and the IC adjusts the motor drive output by changing the output on duty. The low side
output transistor is used for the output PWM switching.
Both the high and low side output diodes are integrated in the IC. However, if reverse torque control mode is selected
for use during deceleration, or if a large output current is used and problems occur (such as incorrect operation or
waveform disruption due to low side kickback), a Schottky diode should be inserted between OUT and ground. Also,
if it is necessary to reduce IC heating during steady-state (constant speed) operation, it may be effective to insert a
Schottky diode between V CC and OUT. (This is effective because the load associated with the regenerative current
during PWM switching is born not by the on-chip diode but by the external diode.)
The current limiter circuit limits the peak level of the current to a level determined by I = VRF/Rf (where VRF =
0.5V (typical) and Rf is the value of the current detection resistor). The current limiter operates by reducing the
output on duty to suppress the current.
The current limiter circuit detects the reverse recovery current of the diode due to PWM operation. To assure that the
current limiting function does not malfunction, its operation has a delay of about 2μs. If the motor coils have a low
resistance or a low inductance, current fluctuations at startup (when there is no reactive power in the motor) will be
rapid. The delay in this circuit means that at such times the current limiter circuit may operate at a point well above
the set current. Designers must take this increase in the current due to the delay into account when setting the current
limiter value.
36
40
48
FRAME
Symbol
VREG
V CC 1
NC
f FG (servo) = f CLK
Stabilized power supply output (5V output).
Insert a capacitor of about 0.1μF between this
pin and ground for stabilization.
Power supply.
Insert a capacitor of at least 10µF between this
pin and ground to prevent noise from entering
the IC.
Since these pins are not connected to the IC
internally, they can be used for wiring
connections.
Connect this pin to ground.
Pin Description
LB11870
Equivalent Circuit
V CC
36
No.7256-11/14