LB1875 데이터 시트보기 (PDF) - SANYO -> Panasonic
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LB1875 Datasheet PDF : 17 Pages
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LB1875
7. PWM frequency
The PWM frequency is determined by the capacitance connected to the C pin.
f PWM =.. 1/(15000 x C)
PWM
The PWM frequency should be between 15 and 50 kHz. If the frequency is too low, noise and control performance may be a
problem. If it is too high, switching losses will increase.
8. LD output
The LD1 output is ON when phase lock is achieved. Phase lock is evaluated only by the phase (through edge comparison), not by
speed deviation. Therefore when LD1 is ON, speed deviation is affected by the FG signal acceleration for example when establishing
the lock condition. (The lower the acceleration, the lower the speed deviation.) When it is necessary to limit speed deviation when
LD1 is ON, the results of actual motor speed measurement must be applied.
9. Power supply
When using FETs as bottom-side output transistors, applying a voltage of 12V to the V pin makes it possible to supply a gate
CC
voltage of about 10V. When using FETs or bipolar transistors that can handle a low gate voltage, the V and V pins can also be
CC
REG
short- circuited to apply 5V. (In this case, do not apply voltage higher than 5.5V.)
Since this IC is designed for use in high-current motors, the power supply line may fluctuate easily. Therefore a capacitor of
sufficient capacitance must be provided between the VCC pin and ground, to assure stable operation. If a diode is used in the power
line for reverse-connection protection, power line fluctuations may be further increased, which will require more capacitance.
10. Motor lock protection circuit
To protect the IC and the motor itself when rotation is inhibited, a motor lock protection circuit is provided. If the LD output is High
(unlocked) for a certain interval in the start condition, the external bottom-side transistors are turned off. The length of the interval
is determined by the capacitance at the CSD pin. A capacitance of 0.1 µF results in a trigger interval of about 10 seconds.
Trigger interval (S) =.. 110 x C (µF)
The trigger interval should be set so as to leave sufficient leeway for motor startup. Speed reduction due to clock frequency switching
does not trigger the protection circuit.
When the protection circuit has been triggered, the condition can only be canceled by setting the system to the stop condition or by
turning the power off and on again. When wishing not to use the motor lock protection circuit, connect the CSD pin to ground.
11. Low voltage protection circuit
The low voltage protection circuit cuts off the bottom-side output transistors (external) when the voltage at the VREG pin falls below
3.75V (typ.). The circuit action is released when the voltage rises above approx. 4.0V (typ.).
12. F/R switching
Forward/reverse switching in principle should be carried out while the motor is stopped. If switching is carried out while the motor
is running, feedthrough current (due to output transistor delay) is prevented by the circuit design, but a high current will flow in the
output transistors (due to counterelectromotive voltage and coil resistance). If such a condition is anticipated, the output transistors
must be selected appropriately, to allow handling even higher current than in normal use.
13. Soft start
In PAM drive mode, connecting a capacitor (approx. 0.01 to 0.1 µF) between the SOFT pin and ground enables soft start (gradual
increase in PWM ON duty cycle, causing a sloped rise in motor supply voltage). This prevents the current flow exceeding the set
current due to switching regulator circuit delay at startup. The Soft start function is active only immediately after motor startup.
When the motor is stopped, the output transistors are turned off, therefore the charge accumulated in the switching regulator smoothing
capacitors can only be discharged as leak current of the output transistors. When the motor is restarted before the supply voltage has
dropped, the soft start function will not be active. Therefore it is necessary to discharge the capacitors via a resistor so that the soft
start function operates properly.
No. 6002-11/17
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