BA6438 データシートの表示（PDF） - ROHM Semiconductor

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BA6438

3-phase motor driver

ROHM Semiconductor 

Motor driver ICs

(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 ~ 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 characteristic

range provides good control over a wide range of current

and good torque characteristics even during overloading.

0

800mA Output current

Output

saturation

voltage

1.5V

HIGH level voltage

Fig.5 High level output voltage vs.

output current (reference curves)

LOW level voltage

1.3V

Output saturation voltage

ATC-pin voltage

Output current

0

800mA

Fig.6 Low level output voltage vs. output

current (reference curves)

(6) Switching regulator

The BA6438S has a switching regulator output pin. The

IC outputs a PWM signal by comparing the output of the

internal oscillator with the HIGH level output voltage

monitored.

BA6438S

VM 24

+

HIGH level

voltage monitor

Oscillator

15

OSC

14 VS

13

REG

Fig. 7

As shown in Fig. 7, the switch 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 transistors.

More power is consumed as the C-E voltage increases and

as the output current increases.

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

between the supply voltage and the voltage applied to the

motor. Because the voltage across the motor decreases 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 excessive voltage is

applied between the transistor collectors 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 excessive 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 BA6438S

contains a short-circuit detection circuit that turns off the motor

drive current if the output-to-ground potential becomes

abnormally low.

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