LB11693H

No.A0287-12/24

12. Undervoltage Protection Circuit

The undervoltage protection circuit turns off the low side output transistor if the LVS

pin voltage falls below the circuit's operating voltage (about 3.8V). This operating

voltage is the detection level for a 5V system. The detection level can be increased by

connecting a zener diode in series with the LVS pin to apply a level shift to the

detection level. The current flowing into the LVS pin during detection is about 65µA.

To suppress variations in the zener voltage, it is necessary to stabilize the rise of the

zener diode voltage by increasing the current that flows in the zener diode. If this is

necessary, insert a resistor between the LVS pin and ground.

When the LCS pin is open, it will be pulled to the ground level by the built-in pull-down resistor and the output will be

turned off. Thus if the undervoltage protection circuit is not used, a voltage in excess of the release voltage (about 4.3V)

must be applied to the LVS pin. Note that the maximum rating for the LVS pin voltage is 30V.

13. Motor Constraint Protection Circuit

When motor motion is constrained, the external capacitor connected to the CSD pin will be alternately charged (up to

about 3.0V) with a constant current of about 2.4µA and discharged with a constant current of about 0.17µA (to about

1.0V). Thus the CSD pin voltage will have a sawtooth waveform. The motor constraint protection circuit turns the

motor (the low side output transistor) on or off repeatedly based on this sawtooth waveform. Motor drive will be on

during the period the CSD pin external capacitor is being charged from about 1.0V to about 3.0V and will be off when

it is being discharged from about 3.0V to about 1.0V. The drive on/off operation protects the IC and the motor when the

motor is physically constrained from moving. If a 0.47µF capacitor is connected to the CSD pin, the IC will iterate an

on/off cycle in which drive is on for about 0.4 seconds and off for about 5.5 seconds.

While the motor is turning, the CSD pin voltage will be held at a certain voltage (that depends on the motor speed) by

(a) a CSD pin external capacitor discharge operation based on about 10µs discharge pulses generated internally in the

IC when the Hall input IN1 switches (that is, on rising and falling edges on the FG output) and (b) a charge operation on

that capacitor by a constant current of about 2.4µA.

Since the Hall input IN1 does not switch when the motor is physically constrained, the discharge pulses are not

generated and the CSD pin external capacitor will be charged to about 3.0V by the constant current of about 2.4µA. The

motor constraint protection circuit operates when the capacitor reaches about 3.0V. The constraint protection operation

will be released when the motor constraint is released.

If the motor speed is extremely low, the CSD pin voltage during that motor rotation will be held at a comparatively high

voltage, and if that voltage reaches about 3.0V, the constraint protection function will operate. Since the constraint

protection function will operate if the Hall input IN1 frequency falls below about 10Hz, caution is required when using

the motor constraint protection circuit with motors that will operate at low speeds.

Connect the CSD pin to ground if the motor constraint protection circuit is not used.