lb11693h Sanyo Semiconductor Corporation, lb11693h Datasheet - Page 11

• Manufacturer Part Number: lb11693h
• Description: 3-phase Brushless Motor Driver For 24v Fan Motors
• Manufacturer: Sanyo Semiconductor Corporation

8. Forward/Reverse Switching
9. Power Saving Circuit
10. Notes on the PWM Frequency
11. Control Methods
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 40kΩ) 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 I O max (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.
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.
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.
The output duty can be controlled by either of the following methods.
• Comparison of the TOC pin voltage with the PWM oscillator waveform
• PWMIN pulse input
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.
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.
LB11693H
No.A0287-11/24