LB1695 데이터 시트보기 (PDF) - SANYO -> Panasonic

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LB1695

Three-Phase Brushless Motor Driver

SANYO -> Panasonic 

LB1695

inertia, certain motor types may cause the VM voltage at the IC to rise and generate voltages that exceed the voltage

handling capacity of the IC.

6.Power supply stabilization capacitor

The low-voltage protection circuit may operate or other problems may occur if large fluctuations occur in the VCC line

voltage. The VCC line must be stabilized by a capacitor (of a few µF) inserted between VCC and ground. Also, the large

switching currents that flow in the VM line can cause fluctuations in the IC VM voltage due to inductive components in

the circuit wiring. The VM line must also be stabilized by a capacitor inserted between VM and ground to prevent

fluctuations in the ground line potential, incorrect operation, and voltages that exceed the voltage handling capacity of

the IC. In particular, applications that have long circuit lines for VM, VCC, and ground must have adequate stabilization

capacitors inserted in the power lines.

7.Current limiter circuit

The current limiter circuit turns off the sink side output transistors when the output current reaches the set limit value

(the limit current). The RF pin is used for current detection, and the output current is detected as a voltage by inserting

the resistor Rf between the RF pin and ground. The current limiter circuit operates when the RF pin reaches 0.5 V

(typical), and thus the output current is limited to the current limit set by the term 0.5/Rf.

7.1 Output off time

After the current limiter circuit operates and turns off the sink side output transistors, it then turns the output on again

after a fixed period (the output off time) has elapsed. This current limiter circuit output switching technique adopted in

the LB1695 is much less susceptible to problems with ASO than are output limitation techniques in which the output is

not operated at the saturated level. The output off time it determined by the charge time for the capacitor connected to

the C pin. When the current limiter circuit operates, the C pin capacitor begins to charge, and the time required to charge

this capacitor to the C voltage, which is 2 volts (typical), is the output off time. When the capacitor is charged to the C

voltage of 2 volts, the sink side output transistors are turned on again. The C pin charge current is a fixed current

determined by the resistor R connected to the R pin. The capacitor charge current ICL and the output off time toff are

related as follows.

ICL ≈ 1.3/R (R must be set to a value in the range 13 to 100 kΩ)

toff ≈ C/ICL × 2.0

≈ 1.53 × R × C

7.2 Output current ignored time

While the current limiter circuit is operating and the sink side output is off, a regenerative current flows in the

external diode provided to absorb regenerative currents in the upper side of the output circuit that was turned off.

When the sink side output is turned off after the output off time has elapsed, a reverse current flows instantaneously

in this diode due to the diode’s reverse recovery time. Due to this phenomenon, a current that may reach the current

limit value flows instantaneously in the output. If the current limiter operated again due to this current, the output

would be turned off and the average current level would fall. This could result in significantly lower torque during,

for example, motor startup. Therefore, to prevent this current from being detected, the current limiter circuit also

provides a fixed period (the output current ignored time) during which the output current is not detected at the point

where the sink side output is turned on again after being turned off. The output current ignored time is determined

by the discharge time for the capacitor connected to the C pin. This discharge starts at the point where the capacitor

is charged to 2 volts following operation of the current limiter circuit. The output current ignored time is the time

for the capacitor to discharge to 0.4 volts (typical). The capacitor discharge current is a fixed current and is set to be

a current about three times the charge current. Therefore, the output current ignored time is about 1/3 the output off

time. The capacitor discharge current ICH and the output current ignored time tsm are related as follows.

ICH ≈ 1.3/R × 3

tsm ≈ C/ICH × 1.6

≈ 0.41 × R × C

Since the current limiter circuit provides a slope to the on time when the sink side output is turned on again, the

reverse circuit never becomes significantly large, even if a rectifying diode (i.e. a diode whose reverse recovery

time is not particularly short) is used as the regenerative current absorption external diode.

7.3 Output off time setting

The output off time must be set to a period optimal for the type of motor used. This time is set by the values of the

external resistor attached to the R pin and the external capacitor attached to the C pin. Figure 1 shows the

waveforms during current limiter operation.

No. 5678-6/7

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