BD6761FS_10 データシートの表示（PDF） - ROHM Semiconductor

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BD6761FS_10

Three-phase Brushless Motor Pre-drivers for Paper Feed

ROHM Semiconductor 

BD6761FS,BD6762FV

Technical Note

●IC Operation

1) Hall input and output

For the hall input signal, the wave is shaped by the hall amplifier 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.

2) PWM operation

PWM oscillating frequency is determined by the triangular waveform frequency which is decided by the external constant.

This triangular waveform voltage and the listed voltage in the following chart are compared to perform PWM drive.

Rfe, RFE

Cfe, CFE

Cfe, CFE pin

Frequency

charge/discharge current I

(Typ.)

Comparison voltage

BD6761FS

50kΩ

1000pF

1.6V/R

16.5kHz

Drive signal shaped by the

hall amplifier

BD6762FV

20kΩ

1000pF

VRFE/R

16kHz

Integration amplifier output

pin voltage

3) Booster circuit (step-up circuit) (common)

BD6761FS (Frequency = 62.5 kHz) and BD6762FV (Frequency = 125 kHz) generate the triangular waveform when the

internal oscillator generates free-run oscillation and the rectangular waveform is generated 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).

Triangular waveform oscillating

Charge pump voltage (VG pin

frequency

voltage)

BD6761FS

62.5 kHz

VCC+6V

BD6762FV

125 kHz

VCC+6.7V

4) FG amplifier (common)

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 uses an open collector format. Use in the condition as it is pulled up to the power supply with the resistor.

At this time, pay attention so that the voltage higher than 36 V is not applied to the FGSOUT pin.

5) ACC, DEC circuits (BD6761FS)

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.

6) Current limit operation

When the CL voltage (BD6761FS) and RF voltage (BD6762FV) become the current limit voltage, the current limit circuit

operates and works to limit 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.

Current limit current

BA6761FS

Iomax=0.48/RNF [A]

BA6762FV

Iomax=0.26/RNF [A]

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© 2010 ROHM Co., Ltd. All rights reserved.

15/22

2010.06 - Rev.A

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