BA6871 Rohm, BA6871 Datasheet - Page 8

• Manufacturer Part Number: BA6871
• Description: 3-phase motor driver
• Manufacturer: Rohm

(4)
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)
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)
The BA6871BS has a series regulator output pin. The IC
outputs a sink current according to the HIGH level output
voltage detected.
680
Motor driver ICs
Motor direction control (pin 29)
Output transistor saturation prevention circuit
Series regulator
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)
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.
Output-to-ground short-circuit detection
BA6871BS