No.8095-11/12

LB11693

possible if the braking current is limited to be under Iomax (1.8 A) by the motor coil resistance or other factors. Also,

since a transient through current will flow at the instant the direction is switched if the direction switching operation is

performed just from the F/R pin, a period where drive is turned off must be provided when switching directions.

Through currents must be prevented by setting the IC to the stop state with the S/S pin or TOC pin to provide a drive off

period where the duty due to the PWMIN pin is set to 0% and switching the F/R pin during that period.

9. Power Saving Circuit

This IC goes to a low-power mode (power saving state) when set to the stop state with the S/S pin. In the power saving

state, the bias currents in most of the circuits are cut off. However, the 5 V regulator output is still provided in the

power saving state.

10. Notes on the PWM Frequency

The PWM frequency is determined by the capacitor C (F) connected to the PWM pin.

It is preferable to use a frequency in the range 15 kHz to 25 kHz for the PWM frequency. The connected capacitor must

be connected to the GND1 pin with a line as short as possible.

11. Control Methods

The output duty can be controlled by either of the following methods

• Control based on comparing the TOC pin voltage to the PWM oscillator waveform

The low side output transistor duty is determined according to the result of comparing the TOC pin voltage to the

PWM oscillator waveform. When the TOC pin voltage is 1.3 V or lower, the duty will be 0%, and when it is 3.0 V

or higher, the duty will be 100%.

Since the TOC pin is the output of the control amplifier (CTL), a control voltage cannot be directly input to the

TOC pin. Normally, the control amplifier is used as a full feedback amplifier (with the EI– pin connected to the

TOC pin) and a DC voltage is input to the EI+ pin (the EI+ pin voltage will become equal to the TOC pin voltage).

When the EI+ pin voltage becomes higher, the output duty increases. Since the motor will be driven when the EI+

pin is in the open state, a pull-down resistor must be connected to the EI+ pin if the motor should not operate when

EI+ is open.

When TOC pin voltage control is used, a low-level input must be applied to the PWMIN pin or that pin connected

to ground.

• Control based on a pulse signal input to the PWMIN pin

A pulse signal with a frequency in the range 15 to 25 kHz can be input to the PWMIN pin, and the duty of the low

side output transistor can be controlled based on the duty of that input signal. Note that the output is on when a low

level is input to the PWMIN pin, and off when a high level is input. When the PWMIN pin is open it goes to the

high level input and the output is be turned off.

When controlling motor operation from the PWMIN pin, the EI– pin must be connected to ground, and the EI+ pin

must be connected to the TOC pin.

12. Undervoltage Protection Circuit

The undervoltage protection circuit turns the low side output transistor off when

the LVS pin voltage falls below the minimum operation voltage (about 3.8 V).

The operating voltage detection level is set up for 5 V systems. The detected

voltage level can be increased by shifting the voltage by inserting a zener diode

in series with the LVS pin. The LVS influx current during detection is about

65 µA. To minimize the effect of sample-to-sample variations in the zener

voltage, the current flowing in the zener diode must be increased thus

stabilizing the rise in the zener diode voltage. If this is required, insert a resistor between the LVS pin and ground.

If the LVS pin is left open, the internal pull-down resistor will result in the IC seeing a ground level input, and the

output will be turned off. Therefore, a voltage in excess of the LVS circuit clear voltage (about 4.3 V) must be applied

to the LVS pin if the application does not use the undervoltage protection circuit. The maximum rating for the LVS pin

applied voltage is 30 V.

13. Constraint Protection Circuit

When the motor is physically constrained (held stopped), the CSD pin external capacitor is charged (to about 3.0 V) by

a constant current of about 2.4 µA and is then discharged (to about 1.0 V) by a constant current of about 0.17 µA. This

process is repeated, generating a sawtooth waveform. The constraint protection circuit turns motor drive (the low side

To the LVS pin

To the power supply

level to be detected