LB1695D 查看數據表（PDF） - SANYO -> Panasonic

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产品描述 (功能)

生产厂家

LB1695D

Three-Phase Brushless Motor Driver for DC Fan

SANYO -> Panasonic 

Continued from preceding page

LB1695D

7. Current limiter circuit

The current limiter circuit cuts off the sink-side output transistors when the output current reaches a preset value

(limiter value). This limits the output current peak value.

For detection of output current, the RF pin is used. By connecting the resistance Rf between the RF pin and

ground, the output current can be detected as a voltage. When the RF pin voltage reaches 0.5V (typ.), the current

limiter is activated. This limits the output current to the value determined by 0.5/Rf.

7-1. Output off time

When the current limiter circuit was triggered and has switched off the sink-side output transistors, it will

turn them on again after a preset interval (power off time). By switching the output in this way, the current

limiter circuit of the LB1695D reduces the likelihood of ASO problems as compared to current limiters using

the non-saturation output principle.

The output off time is determined by the charge time for the capacitance C connected to the C pin. When the

limiter is triggered, C starts to charge, and the time required for the C voltage to reach 2V (typ.) is the output

off time. When C was charged to 2V, the sink-side output is turned on again. The charge current for C is

constant-current and is determined by the resistance R connected to the R pin. The C charge current ICL and

the output off time toff are calculated according to the following equations.

ICL

toff

=.. 1.3/R (R should be between 13 kΩ to 100 kΩ)

=. .

=. .

C/ICL × 2.0

1.53 × R × C

7-2. Output current ignore time

While the sink-side output is turned off by the current limiter, a regenerative current flows in the upper side

regenerative current absorption diode connected externally. When the output off time has elapsed and the

sink-side output is turned on again, a momentary reverse current flows in the external diode (due to the

reverse recovery time of the diode), which causes a limiter-value current to flow momentarily in the output.

If this triggers the current limiter again, the output will be turned off, which lowers the average current and

causes a reduction in motor torque for example during startup. To prevent this, the circuit is designed not to

monitor the output current for a certain period after the sink-side output were turned off and on again. This is

called the output current ignore time.

The output current ignore time is determined by the discharge time of the capacitance C connected to the C

pin. After the current limiter was triggered and C was charged to 2V, the discharge process starts. The time

required to discharge to a voltage of 0.4V (typ.) is the output ignore time. The discharge current for C is

constant-current and is about 3 times the charge current (ICL). Therefore the output current ignore time is

about 1/3 of the output off time.

The C discharge current ICH and the output current ignore time tsm are calculated according to the following

equations.

ICH

tsm

=. .

=. .

=. .

1.3/R × 3

C/ICH × 1.6

0.41 × R × C

Continued on next page

No. 6205-8/10

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