LB11693H

No.A0287-11/24

8. Forward/Reverse Switching

The LB11693H was designed assuming that forward/reverse switching would not be performed while the motor is

operating. We recommend that the F/R pin be held fixed at either the low (forward) or high (reverse) level when the

motor is turning. Although it will be pulled up to the high level by an internal pull-up resistor (about 40k

Ω) when left

open, this must be strengthened by an external resistor if fluctuations are large.

If the direction is switched while the motor is turning, large currents will flow due to the braking operation. The

LB11693H's current limiter circuit, however, cannot limit this braking current. Therefore, forward/reverse switching

during motor rotation is only possible if the braking current is limited to a value under IOmax (1.8A) by the motor coil

resistance or other circuit or phenomenon. Furthermore, since through current will flow in the high and low side

transistors at the instant the switch occurs with switching that only uses the F/R pin, applications must provide a drive

off period for switching directions. A drive off period must be provided by either setting the IC to the stopped state with

the S/S pin or setting the PWM signal to the 0% duty state with the TOC and PWMIN pins, and the F/R pin must only

be switched during that period to prevent through current.

9. Power Saving Circuit

This IC can be set to a power saving state in which current consumption is reduced by setting it to the stopped state with

the S/S pin. The bias current to most of the circuits in the IC is cut off in this power saving state. Note, however, that the

5V regulator output is still provided in the power saving state.

10. Notes on the PWM Frequency

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

fPWM

≈ 1/(23400×C)

A frequency in the range 15 to 25kHz is desirable for the PWM frequency. The ground side of the connected capacitor

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

11. Control Methods

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

• Comparison of the TOC pin voltage with the PWM oscillator waveform

This method determines the low side output transistor duty according to the result of comparing the TOC pin voltage

with the PWM oscillator waveform. The PWM duty will be 0% when the TOC pin voltage is under about 1.3 V and

will be 100% when that voltage is over about 3.0V.

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

Accordingly, the CTL amplifier is normally used as a full feedback amplifier (by connecting the EI− pin to the TOC

pin) and inputting a DC voltage to the EI pin (here the TOC voltage will be equal to the EI+ pin voltage). When the

EI+ pin voltage increases, the output duty will increase as well. Since the motor will be driven if the EI+ pin is in the

open state, a pull-down resistor should be connected to the EI+ pin in applications where this is not desirable.

A low level must be input to the PWMIN pin (or it must be connected to ground) if the TOC pin voltage control

system is used.

• PWMIN pulse input

A 15 to 25kHz frequency pulse signal can be input to the PWMIN pin and the low side output transistor duty can be

controlled based on the duty of that input signal. When the PWMIN pin is low, the output will be on, and when high,

the output will be off. When the PWMIN pin is open, the input will go to the high level and the output will be off.

If PWMIN pin control is used, the EI− pin must be connected to ground and the EI+ pin must be connected to the

TOC pin.