BA6871 データシートの表示（PDF） - ROHM Semiconductor

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BA6871

3-phase motor driver

ROHM Semiconductor 

Motor driver ICs

BA6871BS

(4) Motor direction control (pin 29)

The motor mode is:

Forward when the pin 29 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.

(6) Series regulator

The BA6871BS has a series regulator output pin. The IC

outputs a sink current according to the HIGH level output

voltage detected.

As shown in Fig. 14, the regulator circuit reduces the

power consumed by the IC by reducing the collector-to-

emitter (C-E) voltage of the driver transistors.

Nearly all the power dissipated by the IC is dissipated be-

tween the collectors and emitters of the output transis-

tors. More power is consumed as the C-E voltage in-

creases and as the output current increases.

The output transistor C-E voltage is equal to the differ-

ence between the supply voltage and the voltage applied

to the motor. Because the voltage across the motor de-

creases with decreasing drive current, the C-E voltage

must increase if the supply voltage is fixed.

Therefore, to improve the efficiency of the driver and to

prevent the power rating of the IC being exceeded, the

supply voltage must be varied in response to changes in

the output current. The supply voltage is decreased at

low current and increased at high current so that no ex-

cessive voltage is applied between the transistor collec-

tors and emitters.

(7) Output-to-ground short-circuit detection

The motor output pins of the IC may be short-circuited to

the ground by some fault conditions. A short-circuited

output can destroy the output transistors because of ex-

cessive current, excessive voltage, or both. Even when

a short-circuit condition does not completely destroy the

device, it can still cause extreme overheating. To prevent

this, the BA6871BS contains a short-circuit detection cir-

cuit that turns off the motor drive current if the output-to-

ground potential becomes abnormally low.

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