bd6761fs ROHM Co. Ltd., bd6761fs Datasheet - Page 20

• Manufacturer Part Number: bd6761fs
• Description: Motor Driver Ic Series For Printers Three-phase Brushless Motor Pre-driver For Paper Feed Us
• Manufacturer: ROHM Co. Ltd.

●Selecting application components
①Output FET
②Diodes (BD67861FS)
③Protection capacitor between the output FET drain and source
④VB current capacitance capacitor
⑤PWM frequency
⑥Hall input level
⑦VREG
⑧Current limit
⑨OSC frequency (BA6680FS)
⑩Hall input noise
⑪CL (RF) voltage smoothing low pass filter
⑫FG AMP constant setting
This IC is the predriver for high-side and low-side N-channel MOS
FET drive. Select the FET with the required current capacity to
drive the motor.
Diodes are required to protect between the gate and source of
output FET.
Check the operation so that the voltage between the output FET
drain and source does not exceed the absolute maximum ratings
due to the fluctuation of VCC at the time of PWM driving and then
set the value.
Current capacity from VG changes according to the capacitance to
be connected. However, if the capacitance is too large, the
following action is delayed when VCC starts up, and the magnitude
relation becomes VCC > VG. Typically, should be VCC < VG and
the large current may flow in internal block circuits and result in
damaging the circuits. When VG is directly supplied from the
external block without using the internal circuits, disconnect the
capacitor between CP1 and CP2, and connect the 20kΩ resistor
(for noise reduction) between CP1 and ground to use.
PWM frequency can be adjusted by the capacitance and
resistance to connect. When the frequency is high, the heat
generation increases due to switching loss. When the frequency is
low, it enters audible range. Check the operation with the actual
product and determine the constant.
The current value to feed to the hall element changes by changing
the resistance and the amplitude level of hall element.
Amplitude level increases when the resistance value is chosen
smaller by considering the noise affect. Pay attention to the hall
input voltage range. BA6680FS (1.0V to 4.9V), BD6761FS (1.5V to
4.1V) and BD6762FV (0V to 3V)
VREG which is the internal voltage output pin drives the circuits in
IC. Connect the capacitor to stabilize it.
The current flowing to FET can be controlled by setting the
resistance value. Determine the constant according to the motor
specifications.
Triangular waveform is formed by the capacitance to connect.
Insert capacitors between the hall phases in order to eliminate the
hall input noise due to the effect by the pattern routing design.
Smooth the CL (RF) voltage which has PWM noise through the low
pass filter.
FG AMP gain: GFG is the ratio of R1 and R2 calculated by the
following equation:
Set up the gain so that the FGOUT amplitude is large enough to
the hysteresis level of the hysteresis comparator and it cannot be
clamped by the high and low output voltages (VFGOH and
VFGOL).
GFG=20log R2/R1 [dB]
Design method
20/24
Recommended FET RDS035L03 (A)
Recommended diode 1SS355
Insert the diode in the direction from high-side FET source to
the gate side (in the forward direction).
A value of 0.01μ to 0.1μF is recommended.
A value of 0.1μF is appropriate for the capacitance.
Insert the capacitor between the output FET drain and source.
(Position at the close point to FET as much as possible.)
A value of 0.01μF is appropriate for the capacitor between
CP1 and CP2
(A value of 0.01μF 0.1μF is recommended.)
A value of 0.1μF is appropriate for the capacitor between VG
and VCC.
The following constants are appropriate:
BA6680FS Cfe=100pF, Rfe=50kΩ, fo=15.5kHz(TYP.)
BD6761FS Cfe=1000pF, Rfe=50kΩ, fo=16.5kHz(TYP.)
BD6762FV Cfe=1000pF, Rfe=20kΩ, fo=16.0kHz(TYP.)
Connect to the transistor base via 1kΩ resistor (base current
limit) from the VREG pin. Connect the transistor collector to
VCC, the emitter to the hall element via R1. Connect the ground
side of hall element to the ground via R2.
A value of 200Ω to 1kΩ is recommended. A value of 200Ω is
appropriate. When connecting to the VCC side directly with R1,
values of R1=5kΩ and R2=2kΩ are appropriate.
A value of 0.01μF to 0.1μF is recommended. A value of 0.1μ
is appropriate.
Following equation shows the current value:
BA6680FS
BD6761FS
BD6762FV
A value of C=100pF and Frequency=95kHz (Typ.) is
appropriate.
A value of 0.01μ F is appropriate for the capacitor to be
installed between the hall phases.
A value of 0.01μF to 0.1μF is recommended.
A value of C = 470pF and R=1kΩ is appropriate for the low
pass filter.
For the external constant, since the impedance is high, make
sure to design the pattern with the shortest circuit route so that
the circuit is hard to be affected by noise.
R1 and C1 form a high pass filter and R2 and C2 form a low
pass filter. Each cut off frequency; f
the following equation:
f
Set the value so that the main signal from PG by the motor is
not attenuated but the unnecessary noise.
MPF
=1/2πR1C1, f
Iomax=0.38/RNF [A]
Iomax=0.48/RNF [A]
Iomax=0.26/RNF [A]
LPF
=1/2πR2C2
Design example
MPF
and
fLPF
is determined by