bd6761fs ROHM Co. Ltd., bd6761fs Datasheet - Page 17

• 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.

●IC Operation
1)
2)
3)
4)
5)
6)
7)
Hall input and output
PWM operation
Boost circuit (step-up circuit) (common)
FG amplifier (common)
ACC, DEC circuits (BA6680FS､BD6761FS)
Current limit operation
Preventing low-side and high-side switch overlapping (BD6761FS, BD6762FV)
The hall amplifier shapes the hall input signal to generate the drive signal.
This drive signal is amplified in the predriver block and the gate voltage is output for N-channel MOS FET.
PWM oscillating frequency is determined by the triangular waveform frequency which is set by the external constant.
This triangular waveform voltage and the listed voltage in the following chart are compared to perform PWM drive.
BA6680FS
BD6761FS
BD6762FV
BA6680FS generates the triangular waveform by connecting a capacitor (COSC = 100pF: Frequency = 95 kHz) between the OSC
and GND pins. BD6761FS (Frequency = 62.5 kHz) and BD6762FV (Frequency = 125 kHz) generate the triangular waveform by the
internal free-run oscillator and the rectangular waveform at CP1. When a capacitor is connected between CP1 and CP2, and VG and
GND, the step-up voltage is generated at VG pin. In this case, set VCC so that VG does not exceed the absolute maximum ratings
(36 V).
BA6680FS
BD6761FS
BD6762FV
Set the FG amplifier gain so that the FGOUT pin is within the range of high and low output voltage and the amplitude is higher than
the hysteresis width (250 mV: max) of the HYS amplifier.
FGSOUT pin is an open collector which requires a resistor to the supply line. Voltage higher than 36 V must not be applied to the
FGSOUT pin.
When a resistor is connected to the RCP pin and the low voltage is input to the ACC pin, the current flows out from the CPOUT pin.
When the low signal is input to the DEC pin, the current flows in to the CPOUT pin. Furthermore, when the ACC pin and DEC pin both
set to low, the current flows in to the CPOUT pin. This current can be converted to the voltage by connecting a filter between the
CPOUT and GND pins.
The voltage generated at the CPOUT pin controls the PWM's on-duty and maintains the constant motor rotation by inputting the
controlled signal to ACC and DEC pins.
The CL voltage (BA6680FS, BD6761FS) and RF voltage (BD6762FV) become the current limit voltage and the current limit circuit
limits PWM on_dutty. It also turns off the current limit circuit (current limit clear) at the peak of PWM triangular waveform and makes
the current flow again. Output current Iomax at this time are shown in the table.
BA6680FS
BA6761FS
BA6762FV
When the low-side gate voltage becomes high while the high-side gate voltage is low, or vice versa, a prevention delay time is
provided with t=3.2 µs (TYP value). When the input capacity of external FET is C and the gate connection resistor is R, set R to
satisfy the following equation:
Note: Confirm by testing on the actual system.
C
≦
Rfe, RFE
10
50kΩ
50kΩ
20kΩ
×
（ 24
1.8μ
Current limit current
Iomax=0.38/RNF [A]
Iomax=0.48/RNF [A]
Iomax=0.26/RNF [A]
Triangular waveform oscillating
+
Cfe, CFE
R ）
1000pF
1000pF
100pF
95kHz(COSC=100pF)
frequency
62.5 kHz
125 kHz
charge/discharge current I
Cfe, CFE pin
17/24
VRFE/R
0.4V/R
1.6V/R
Charge pump voltage (VG pin voltage)
Frequency
VCC+6.7V
15.5kHz
16.5kHz
VCC+7V
VCC+6V
16kHz
(Typ.)
Pref
Drive signal shaped by the hall
amplifier
Integration amplifier output pin
voltage
Comparison voltage