BA6870S View Datasheet(PDF) - ROHM Semiconductor

Part Name

Description

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BA6870S

3-phase motor driver

ROHM Semiconductor 

Motor driver ICs

(2) Torque control and reversal brake

The output current can be controlled by adjusting the

voltage applied to the torque control pins (pins 15 and

16).

BA6870S

These pins are the inputs to a differential amplifier. A ref-

erence voltage between 2.3 X 3.0V (2.5V recommended)

is applied to pin 15.

A brake is applied to the motor as described in the follow-

ing. When the motor is running, pin 16 is given a negative

potential with respect to the reference potential. If the

pin-16 potential becomes positive, the IC detects the rise

of pin-16 potential above the reference potential and acti-

vates the motor direction detecting circuit.

The motor direction detecting circuit sends a signal to the

motor direction setting circuit to reverse the motor direc-

tion. This causes a braking torque that depends on the

pin-16 potential, so that the motor quickly reduces its

speed. At the same time, the positive pin-16 potential is

shifted to the reference potential, so that the motor stops

smoothly.

(3) Output current sensing and torque limitation

Pin 2 is the ground pin for the output stage. To sense the

output current, a resistor (0.5Ω recommended) is con-

nected between pin 2 and the ground. The output current

is sensed by applying the voltage developed across this

resistor to pin 18 as a feedback.

The output current can be limited by adjusting the voltage

applied to pin 17. The current is limited when pin 17

reaches the same potential as pin 18. The output current

(IMax.) under this condition is given by:

IMAx. =

V17P*(TL*CSofs)

R2P

Where R2P is the value of the resistor connected between

pin 2 and the ground, V17P is the voltage applied to pin 17,

and (TL*CSofs) is the offset between the TL and CS pins.

(4) Motor direction control (pin 11)

The motor mode is:

Forward when the pin 11 voltage is less than 0.9V,

Stop when the voltage is between 1.3 X 3.0V,

Reverse when the voltage is above 3.5V.

In the stop mode, high- and low-side output transistors

are turned off, resulting in a high impedance state.

(5) Output transistor saturation prevention circuit

This circuit monitors the output voltage and maintain the

operation of the output transistors below their saturation

levels. Operating the transistors in the linear characteris-

tic range provides good control over a wide range of cur-

rent and good torque characteristics even during over-

loading.

669

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