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LB1821M View Datasheet(PDF) - SANYO -> Panasonic

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LB1821M Datasheet PDF : 16 Pages
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LB1821M
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. The external
resistor must not have a value under 30 k.
7. Hall Input Signals
Input signals with an amplitude greater than the hysteresis (60 mV, maximum) are required for the Hall inputs. An
input amplitude of 100 mV or greater is desirable, taking noise and other considerations into account. The Hall input
DC voltage must be set to fall within the common-mode input voltage range specifications.
8. Forward/Reverse (F/R) Switching
The F/R pin can be used to switch the motor direction. The direction can be switched with the F/R pin even if the
motor is turning. The IC circuit is designed to compensate for the through currents that occur when the direction is
switched. However, caution is required with respect to increases in the VCC voltage (due to motor current returning to
the power system instantaneously) during direction switching. If this is a problem, try increasing the capacitance of
the capacitor connected between the power supply and ground.
9. Brake Switching
The LB1821M implements a short braking technique in which the upper side transistors (the external transistors) for
all phases are turned on. (The lower side transistors for all phases are turned off.) This means that the output current
during braking does not pass through the Rf (the current detection resistor) and therefore that the current limiter does
not function. Thus caution is required. During braking, the upper side transistors operate at a 100% duty, regardless
of the motor speed. The braking function can be operated and released in the start state. Thus motor start and stop
control can be performed from the brake pin with the S/S pin at the low level, i.e., with the system in the start state. If
the startup time is a problem, the motor can be started with a shorter startup time by using the brake pin for motor
start/stop control than it can with the S/S pin. (This is because the stop state is a power saving state, and restarting
from this state requires waiting the time required for the VCO circuit to stabilize.)
10. Constraint Protection Circuit
The LB1821M 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.
<Set time (s)> 44 × C (µF)
To release the constraint protection state, the LB1821M must be set to either the stop state or the brake state, or
power must be reapplied. The CROCK pin must be connected to ground if the constraint protection circuit is not
used. However, note that the clock disconnection protection circuit described later cannot be used in this case.
11. Clock Disconnection Protection Circuit
If clock input stops with the LB1821M in the start state, this protection circuit operates and turns off the (external)
upper side output transistors. If the clock is reapplied, the IC resumes operation.
12. Low-Voltage Protection Circuit
The LB1821M includes a low-voltage protection circuit to protect against incorrect operation when power is first
applied or if the power-supply voltage (VCC) falls. The (external) upper side output transistors are turned off if VCC
falls under about 3.75 volts, and this function is cleared at about 4.0 volts.
13. Power Supply Stabilization
Since this IC is used in applications that draw large output currents, the power-supply line is subject to fluctuations.
Therefore, capacitors with capacitances adequate to stabilize the power-supply voltage must be connected between
the VCC pin and ground. If diodes are inserted in the power-supply line to prevent IC destruction due to reverse
power supply connection, since this makes the power-supply voltage even more subject to fluctuations, even larger
capacitors will be required.
14. Ground Lines
The signal system ground and the output system ground must be separated and a single ground point must be taken at
the connector. Since the output system ground carries large currents, this ground line must be made as short as
possible.
No. 5686-9/16
 

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