bd6709fs ROHM Co. Ltd., bd6709fs Datasheet - Page 24

• 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.

2) Current limit (current limiting circuit)
The current limit circuit turns off the output, when the current that flows to the motor coil is detected exceeding a set
value.
The current value that current limit operates is determined by
a) Voltage of CL terminal and voltage of RNF terminal (BD6709FS, BD6718FV)
b) Internal setting voltage and voltage of RNF terminal (BD6721FS, BD6722FS)
a) Setting according to voltage of CL terminal and RNF terminal.
b) Setting according to internal voltage and RNF terminal.
Both of a) and b)
R3 and C1 are low-pass filters for RNF smooth voltage. Adjust for a current limit not to malfunction in proportion to the
PWM frequency.
Connect the capacitor with the COSC terminal to do the resume operation after a current limit operates at the PWM
operation by the pulse input.
For example about BD6718FV, in Fig.82
When R1=40k Ω、 R2=10k Ω、 R4=0.5 Ω , the amperage I that current limit operates is
For example about BD6722FS, in Fig.83
Current limit circuit operates at 1A.
Short CL terminal to VREF, short CS and RNF terminal to GND when the current limit function is not used.
When R4=0.33 Ω , the current limit setting voltage is 350mV(typ.)
Current limit circuit operates at 1.06A.
Short CS and RNF terminal to GND when the current limit function is not used.
Fig.82 External setting of current limit voltage
I =
I =
V1 =
R1
V1
R2
VREF
350mV
0.33 Ω
V1
R4
C1
R1
R2
+
=
=1.06A
R2
R3
R4
0.5
0.5
× VREF =
CL
CS
RNF
= 1A
-
+
40k
10k
+
10k
× 2.5 = 0.5V
24/40
Fig.83 Internal setting of current limit voltage
C1
R3
R4
Reference voltage
CS
RNF
-
+