LB1975

No.6087-9/10

7. Start/Stop Control Circuit

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).

8. Forward/Reverse Switching

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 (IO) 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: VCTL≤ VCTL1 (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.

9. VCC, VM Power Supplies

When the power supply voltage (VCC, VM) 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 VCC is likely to cause feed-through current. This should be prevented by

ensuring that

∆VCC / ∆t = 0.2V/µs or less. Feed-through current can also be prevented by first switching on VCC and

then VM 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

VCTL pin. When the motor has come to a full stop, switch off VM and then VCC. 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 VM side, depending on the motor type and power-off

procedure. If this current cannot be absorbed by the VM power supply or a capacitor, VM voltage may rise and exceed

the absolute maximum VM rating for the IC. Ensure that this does not happen through proper design of the VM 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 VCC

(6.3V typ.) to the VREG pin via an external NPN transistor and resistor. When not using the regulator, leave the VREG

pin open.

10. Power Supply Stabilizing Capacitors

If the VCC line fluctuates drastically, the low-voltage protection circuit may be activated by mistake, or other

malfunctions may occur. The VCC line must therefore be stabilized by connecting a capacitor of at least several µF

between VCC and GND. Because a large switching current flows in the VM line, wiring inductance and other factors

can lead to VM voltage fluctuations. As the GND line also fluctuates, the VM line must be stabilized by connecting a

capacitor of at least several µF between VM and GND, to prevent exceeding VM max or other problems. Especially

when long wiring runs (VM, VCC, GND) are used, sufficient capacitance should be provided to ensure power supply

stability.

11. VCREF Pin, VCOUT Pin

These pins are always used in the Open condition. If chattering occurs in the PWM switching output, connect a

capacitor (about 0.1

µF) between VCREF and ground or between VCOUT and GND.

12. IC Heat Dissipation Fins

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.