bd6709fs ROHM Co. Ltd., bd6709fs Datasheet - Page 37

• 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.

●Calculation of power consumed by IC
3) Problem of GND line PWM switching
4) FG and AL output
Do not perform PWM switching of GND line because GND terminal potential cannot be kept to a minimum.
FG and AL output is an open collector and requires pull-up resistor.
The IC can be protected by adding resistor R1. An excess of absolute maximum rating, when FG or AL output terminal
is directly connected to power supply, could damage the IC.
Power consumed by this IC Pc is approximately calculated as follows:
・Pc1：Power consumption by circuit current
・Pc2：Power consumption at output stage
・Pc3：Power consumption at FG and AL
Power consumption by IC greatly changes with use condition of IC such as power supply voltage and output current.
Consider thermal design so that the maximum power dissipation on IC package is not exceeded.
Pc=Pc1+Pc2+Pc3
Pc2=VOL×Io+VOH×Io
VOL is L voltage of output terminal 1 and 2.
VOH is H voltage of output terminal 1 and 2.
Pc3=VFG×IFG＋VAL×IAL
VFG is L voltage of FG output.
VAL is L voltage of AL output.
IFG and IAL are the current of FG and AL.
Pc1=Vcc×Icc
Io is the current flowing to output terminal 1 and 2.
M
Fig.100 GND line PWM switching prohibited
Fig.101 Protection of FG and AL terminal
Driver
Motor
GND
Vcc
FG /AL
Prohibite
37/40
PWM input
resistor R1
Protection
Pull-up
resistor
Vcc
Connector
of board
Fig.102 Calculation of power consumed by
Controller
Vcc
Icc
OUT1
OUT2
FG
Io
IFG