LB1975_08 SANYO [Sanyo Semicon Device], LB1975_08 Datasheet - Page 9

• Manufacturer Part Number: LB1975_08
• Description: For Fan Motor 3-phase Brushless Motor Driver
• Manufacturer: SANYO [Sanyo Semicon Device]

7. Start/Stop Control Circuit
8. Forward/Reverse Switching
9. V CC , V M Power Supplies
10. Power Supply Stabilizing Capacitors
11. V CREF Pin, V COUT Pin
12. IC Heat Dissipation Fins
The start/stop control circuit turns the source-side output transistors OFF (motor stop) when a High signal is input at the
S/S pin or when the pin is Open. When a Low signal is input at the S/S pin, the source-side output transistors are turned
ON, and the normal operation state is established (motor start).
The LB1975 is designed under the assumption that forward/reverse switching is not carried out while the motor is
running. If switching is carried out while the motor is running, reverse torque braking occurs, leading to a high current
flow. If the current limiter is triggered, the source-side output transistors are switched off, and the sink-side output
transistors go into the short brake condition. However, because the current limiter of this IC cannot control the current
flowing in the sink-side output transistors, these may be destroyed by the short brake current. Therefore F/R switching
while the motor is running is permissible only if the output current (I O ) is limited to a maximum of 2.5A using the
motor coil resistance or other suitable means.
F/R switching should be carried out only while a High signal is input to the S/S pin or the pin is Open (stop condition),
or while the VCTL pin conforms to the following condition: V CTL ≤ V CTL 1 (duty cycle 0%). In any other condition,
F/R switching will result in feed-through current. The F/R pin should therefore be fixed to Low (forward) or High or
Open (reverse) during use.
When the power supply voltage (V CC , V M ) rises very quickly when a power is first applied, a feed-through current
may occur at the output. If the current remains below about 0.2A to 0.3A, it does not pose a problem, but such a
possibility should still be prevented by slowing down the voltage rise at power-on. Especially if the F/R pin is set to
High or Open (reverse), a quick rise in V CC is likely to cause feed-through current. This should be prevented by
ensuring that ∆V CC / ∆t = 0.2V/µs or less. Feed-through current can also be prevented by first switching on V CC and
then V M during power-on.
The sequence at power-down should be as follows. Provide a stop input to the S/S pin or a duty ratio 0% input to the
V CTL pin. When the motor has come to a full stop, switch off V M and then V CC . If power is switched off while the
motor is still rotating or a current is flowing in the motor coil (including motor restraint or inertia rotation), a counter
electromotive current or kickback current may flow on the V M side, depending on the motor type and power-off
procedure. If this current cannot be absorbed by the V M power supply or a capacitor, V M voltage may rise and exceed
the absolute maximum V M rating for the IC. Ensure that this does not happen through proper design of the V M power
supply or through use of a capacitor.
Because the LB1975 incorporates a shunt regulator, it can be used on a single power supply. In this case, supply V CC
(6.3V typ.) to the V REG pin via an external NPN transistor and resistor. When not using the regulator, leave the V REG
pin open.
If the V CC line fluctuates drastically, the low-voltage protection circuit may be activated by mistake, or other
malfunctions may occur. The V CC line must therefore be stabilized by connecting a capacitor of at least several µF
between V CC and GND. Because a large switching current flows in the V M line, wiring inductance and other factors
can lead to V M voltage fluctuations. As the GND line also fluctuates, the V M line must be stabilized by connecting a
capacitor of at least several µF between VM and GND, to prevent exceeding V M max or other problems. Especially
when long wiring runs (V M , V CC , GND) are used, sufficient capacitance should be provided to ensure power supply
stability.
These pins are always used in the Open condition. If chattering occurs in the PWM switching output, connect a
capacitor (about 0.1µF) between V CREF and ground or between V COUT and GND.
A heat sink may be mounted to the heat dissipation fins of this IC, but it may not be connected to GND. The sink should
be electrically open.
LB1975
No.6087-9/10