LB11850VA-TLM-H 查看數據表（PDF） - ON Semiconductor

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LB11850VA-TLM-H

Single‐phase Full‐wave Pre‐driver with Speed Control Function for Fan Motor

ON Semiconductor 

LB11850VA

3. Additional Description of Operations:

The LB11850 forms a feedback loop inside the IC so that the FG period (motor speed) corresponding to the control

voltage is established by inputting the duty pulse.

LB11850VA

CTL

CTL

signal

Speed control block

FG

Closed

Feed−back

Loop

CONTROL

SIGNAL

Pre−driver block

Figure 6. Additional Description of Operations

The operation inside the IC is as follows. Pulse signals are created from the edges of the FG signals as shown in the figure

below, and a waveform with a pulse width which is determined by the CR time constants and which uses these edges as

a reference is generated by a one-shot multivibrator.

These pulse waveforms are integrated and the duty ratio of the pre-driver output is controlled as a control voltage.

FG

EDGE pulse

RC pin

Slope due to

CR time

constant

1 shot output

TRC(s) = 1.15RC

Figure 7. Pulse Waveforms

Furthermore, by changing the pulse width as determined by the CR time constant, the VCTL versus speed slope can be

changed as shown in the speed control diagram of the previous section.

However, since the pulses used are determined by the CR time constant, the variations in CR are output as-is as the speed

control error.

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