lb11961 Sanyo Semiconductor Corporation, lb11961 Datasheet - Page 6

• Manufacturer Part Number: lb11961
• Description: 12v Single-phase Bipolar Drive Variable Speed Fan Motor Driver
• Manufacturer: Sanyo Semiconductor Corporation

Control Timing Chart
(V CC × 28%)
Internal lowest speed setting voltage
RMI voltage
1. Set minimum speed mode
2. High speed ↔ low speed mode
3. Full-speed mode
4. Thermistor removed mode
0V
0V
A VTH voltage level is generated when the thermistor detects the set temperature. At low temperatures, the fan
motor turns at the lowest speed, which is set with the RMI pin. The LB11961 compares the CPWM oscillator
voltage with the RMI pin voltage and sets the duty for the lowest drive state.
The PWM signal is controlled by comparing the CPWM oscillation voltage that cycles between 1.2V and 3. 8V
and the VTH voltage.
When the VTH voltage is lower, the high and low side transistors are turned on, and when the VTH voltage is
higher, the high side transistor is turned off and the coil current is regenerated through the low side transistor.
Thus the output on duty increases as the VTH voltage becomes lower, the coil current increases, and the motor
speed increases.
Rotation speed feedback is provided by the FG output.
The LB11961 switches to full-speed mode above a certain temperature.
If the thermistor is removed, the VTH input voltage will rise. However, the output will go to full drive at 100%
and the motor will run at full speed.
CPWM
V CC
FG
Set minimum
speed
Low on duty
f = 25kHz (CP=100pF)
Low
temperature
PWM control variable speed mode
LB11961
High on duty
High
temperature
Full speed mode
Thermistor removed
(V CC × 16%)
3.6V
(V CC × 30%)
2.0V
12V
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