bd6709fs ROHM Co. Ltd., bd6709fs Datasheet - Page 21

• Manufacturer Part Number: bd6709fs
• Description: Dc Brushless Motor Drivers For Cooling Fans Speed Controllable Single-phase Full-wave Dc Brushless Fan Motor Drivers
• Manufacturer: ROHM Co. Ltd.

●Description of operations
Function table
1) Variable speed operation
Variable speed control
Current limit
Lock protection and automatic restart
Output Tr simultaneous ON preventing
circuit
High voltage application
PWM soft switching
Soft start
a) PWM operation by DC input
BD6709FS
BD6721FS
BD6718FV
BD6722FS
a) PWM operation by DC input (Method by self-oscillation connecting a capacitor to COSC terminal)
b) PWM operation by pulse input (Method to change duty by inputting pulse directly to COSC terminal)
As shown in Fig.73, DC voltage input from LAOUT(BD6709FS, BD6721FS), or DC voltage input from VTH(BD6718FV,
BD6722FS)are compared with triangle wave produced by charging and discharging current to the capacitor connected
to COSC to change ON-DUTY.
VMIN terminal is for setting the minimum rotating speed. ON-DUTY is determined by either VTH terminal voltage or
LAOUT terminal voltage, whichever is lower.
COSC H and COSC L voltage is generated by dividing resistance of internal power supply, and the ratio of those voltage
are designed to be hard to fluctuate.
When the input voltage at LAOUT terminal is constant, effect by fluctuation of COSCH and COSCL voltage is large.
However, by setting that voltage input via VTH terminal is generated by dividing resistance of VREF terminal voltage,
application can be made hard to be affected by voltage fluctuation of triangle wave. For an application which requires
strict precision, determine a value with sufficient margin after full consideration of external constant is taken.
Rotating speed changes by PWM ON-DUTY on the upper output.
PWM operation enables
OSC H voltage
OSC L voltage
VMIN
OUT
A1H
A2H
Output is ON when COSC terminal voltage＞VTH terminal voltage or LAOUT terminal voltage
Output is OFF when COSC terminal voltage＜VTH terminal voltage of LAOUT terminal voltage
①
DC input
PWM input
Fig.73 DC input PWM operation timing chart
②
BD6709FS
〇
〇
〇
〇
21/40
BD6718FV
〇
〇
〇
〇
〇
〇
③
BD6721FS
〇
〇
〇
〇
〇
LAOUT or VTH
①Full torque operating area
②ON-Duty set by VTH terminal
③ ON-Duty set by VMIN terminal
voltage (thermistor voltage)
determines the rotating speed.
determines the rotating speed.
BD6722FS
：High impedance
〇
〇
〇
〇
〇
〇
〇
Reference
P.21,22
P.25,26
page
P.23
P.24
P.26
P.27
P.29
P.30