LB11922_08 Datasheet, PDF (13/15 Pages) Sanyo Semicon Device – For OA Products Three-Phase Brushless Motor Driver

LB11922
(2) External clock (A frequency equivalent to that of the crystal oscillator circuit : a few MHz)
If a signal from an external signal source with a frequency equivalent to that of the crystal oscillator circuit is used,
input that signal to the IC through a series resistor (example value : 5.1kΩ). In this case, the XO pin must be left
open.
Input signal levels (signal source)
Low-level voltage : 0 to 0.8V
High-level voltage : 2.5 to 5.0V
3. Output Drive Circuit
To reduce power loss in the output, this IC adopts the direct PWM drive technique. The output transistors (which are
external to the IC) are always saturated when on, and the motor drive output is adjusted by changing the duty with
which the output is on. The PWM switching is performed on the high side for each phase (UH, VH, and WH). The
PWM switching side in the output can be selected to be either the high or low side depending on how the external
transistors are connected.
4. Current Limiter Circuit
The current limiter circuit limits the (peak) current at the value I = VRF/Rf (VRF = 0.26V (typical), Rf : current
detection resistor). The current limitation operation consists of reducing the output duty to suppress the current.
High accuracy detection can be achieved by connecting the RF and RFGND pin lines near the ends of the current
detection resistor (Rf).
5. Speed Lock Range
The speed lock range is ±6.25% of the fixed speed. When the motor speed is in the lock range, the LD pin (an open
collector output) goes low. If the motor speed goes out of the lock range, the motor on duty is adjusted according to the
speed error to control the motor speed to be within the lock range.
6. Notes on the PWM Frequency
The PWM frequency is determined by the capacitor (F) connected to the PWM pin.
When VCC = 6.3V : fPWM ≈ 1/(82000 × C)
When VCC = 5.0V : fPWM ≈ 1/(66000 × C)
A PWM frequency of between 15 and 25kHz 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 23) with lines that are as
short as possible.
7. Hall effect sensor input signals
An input amplitude of over 100mVp-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 commonmode
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.
No.7497-13/15