LB11923V Datasheet, PDF (17/20 Pages) Sanyo Semicon Device – Three-Phase Brushless Motor Driver

LB11923V
6. Notes on the PWM Frequency
The PWM frequency is determined by the capacitor (F) connected to the PWM pin.
When V_CC = 6.3 V: f_PWM ≈ 1/(82000 × C)
When V_CC = 5.0 V: f_PWM ≈ 1/(66000 × C)
A PWM frequency of between 15 and 25 kHz is desirable. If the PWM frequency is too low, the motor may resonate
at the PWM frequency during motor control, and if that frequency is in the audible range, that resonation may result
in audible noise. If the PWM frequency is too high, the output transistor switching loss will increase. To make the
circuit less susceptible to noise, the connected capacitors must be connected to the GND pin (pin 29 and pin 30) with
lines that are as short as possible.
7. Hall effect sensor input signals
An input amplitude of over 100 mV p-p is desirable in the Hall effect sensor inputs. The closer the input waveform is
to a square wave, the lower the required input amplitude. Inversely, a higher input amplitude is required the closer the
input waveform is to a triangular wave. Also note that the input DC voltage must be set to be within the common-
mode input voltage range.
If noise on the Hall inputs is a problem, that noise must be excluded by inserting capacitors across the inputs. Those
capacitors must be located as close as possible to the input pins.
When the Hall inputs for all three phases are in the same state, all the outputs will be in the off state.
If a Hall sensor IC is used to provide the Hall inputs, those signals can be input to one side (either the + or - side) of
the Hall effect sensor signal inputs as 0 to VCC level signals if the other side is held fixed at a voltage within the
common-mode input voltage range that applies when a Hall effect sensors are used.
8. Forward/Reverse Switching
The motor rotation direction can be switched using the F/R pin. However, the following notes must be observed if the
motor direction is switched while the motor is turning.
• This IC is designed to avoid through currents when switching directions. However, increases in the motor supply
voltage (due to instantaneous return of motor current to the power supply) during direction switching may cause
problems. The values of the capacitors inserted between power and ground must be increased if this increase is
excessive.
• If the motor current after direction switching exceeds the current limit value, the PWM drive side outputs will be
turned off, but the opposite side output will be in the short-circuit braking state, and a current determined by the
motor back EMF voltage and the coil resistance will flow. Applications must be designed so that this current does
not exceed the ratings of the output transistors used. (The higher the motor speed at which the direction is
switched, the more severe this problem becomes.)
9. Brake Switching
The LB11923V provides short-circuit braking implemented by turning the output transistors for the high side for all
phases (UH, VH, and WH) on. (The opposite side transistors are turned off for all phases.) Note that the current
limiter does not operate during braking. During braking, the duty is set to 100%, regardless of the motor speed. The
current that flows in the output transistors during braking is determined by the motor back EMF voltage and the coil
resistance. Applications must be designed so that this current does not exceed the ratings of the output transistors
used. (The higher the motor speed at which braking is applied, the more severe this problem becomes.)
The braking function can be applied and released with the IC in the start state. This means that motor startup and stop
control can be performed using the brake pin with the S/S pin held at the low level (the start state). If the startup time
becomes excessive, it can be reduced by controlling motor startup and stop with the brake pin rather than with the S/S
pin. (Since the IC goes to the power saving state when stopped, enough time for the VCO circuit to stabilize will be
required at the beginning of the motor start operation.)
10. Constraint Protection Circuit
The LB11923V includes an on-chip constraint protection circuit to protect the IC and the motor in motor constraint
mode. If the LD output remains high (indicating the locked state) for a fixed period in the start state, the upper side
(external) transistors are turned off. This time is set by the capacitance of the capacitor attached to the CROCK pin. A
time of a few seconds can be set with a capacitance of under 0.1 µF.
No. 7498-17/20