LB11620T-TLM-E Datasheet, PDF (12/13 Pages) ON Semiconductor – Brushless Motor Driver

LB11620T
5. Hall Input Signals
A signal input with an amplitude in excess of the hysteresis (80mV maximum) is required for the Hall inputs.
Considering the possibility of noise and phase displacement, an even larger amplitude is desirable.
If disruptions to the output waveforms (during phase switching) or to the HP output (Hall signal output) occur due to
noise, this must be prevented by inserting capacitors across the inputs. The constraint protection circuit uses the Hall
inputs to discriminate the motor constraint state. Although the circuit is designed to tolerate a certain amount of noise,
care is required when using the constraint protection circuit.
If all three phases of the Hall input signal system go to the same input state, the outputs are all set to the off state (the UL,
VL, WL, UH, VH, and WH outputs all go to the low level).
If the outputs from a Hall IC are used, fixing one side of the inputs (either the + or – side) at a voltage within the
common-mode input voltage range allows the other input side to be used as an input over the 0V to VCC range.
6. Under-voltage Protection Circuit
The under-voltage protection circuit turns one side of the outputs (UH, VH, and WH) off when the VREG pin voltage
falls below the minimum operation voltage (see the Electrical Characteristics). To prevent this circuit from repeatedly
turning the outputs on and off in the vicinity of the protection operating voltage, this circuit is designed with hysteresis.
Thus the output will not recover until the operating voltage rises 0.5V (typical).
7. 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 2.25μA and is then discharged (to about 1.0V) by a constant current of about 0.15μA.
This process is repeated, generating a saw-tooth waveform. The constraint protection circuit turns motor drive on and
off repeatedly based on this saw-tooth waveform. (The UH, VH, and WH side outputs are turned on and off.) Motor
drive is on during the period the CSD pin external capacitor is being charged from about 1.0V to about 3.0V, and motor
drive is off during the period the CSD pin external capacitor is being discharged from about 3.0V to about 1.0V.
The IC and the motor are protected by this repeated drive on/off operation when the motor is physically constrained.
The motor drive on and off times are determined by the value of the connected capacitor C (in µF).
TCSD1 (drive on period) ≈ 0.89 × C (seconds)
TCSD2 (drive off period) ≈ 13.3 × C (seconds)
When a 0.47μF capacitor is connected externally to the CSD pin, this iterated operation will have a drive on period of
about 0.4 seconds and a drive off period of about 6.3 seconds.
While the motor is turning, the discharge pulse signal (generated once for each Hall input period) that is created by
combining the Hall inputs internally in the IC discharges the CSD pin external capacitor. Since the CSD pin voltage
does not rise, the constraint protection circuit does not operate.
When the motor is physically constrained, the Hall inputs do not change and the discharge pulses are not generated.
As a result, the CSD pin external capacitor is charged by a constant current of 2.5μA to about 3.0V, at which point the
constraint protection circuit operates. When the constraint on the motor is released, the constraint protection function is
released.
Connect the CSD pin to ground if the constraint protection circuit is not used.
8. Forward/Reverse Direction Switching
This IC is designed so that through currents (due to the output transistor off delay time when switching) do not flow in
the output when switching directions when the motor is turning. However, if the direction is switched when the motor
is turning, current levels in excess of the current limiter value may flow in the output transistors due to the motor coil
resistance and the motor back EMF state when switching. Therefore, designers must consider selecting external output
transistors that are not destroyed by those current levels or only switching directions after the speed has fallen below a
certain speed.
9. Handling Different Power Supply Types
When this IC is operated from an externally supplied 5V power supply (4.5 to 5.5V), short the VCC pin to the VREG
pin and connect them to the external power supply.
When this IC is operated from an externally supplied 12V power supply (8 to 17 V), connect the VCC pin to the power
supply. (The VREG pin will generate a 5V level to function as the control circuit power supply.)
No.A0662-12/11